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Spectroscopic Insights into the Influence of Filling Carbon Nanotubes with Atomic Nanowires for Photophysical and Photochemical Applications
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Spectroscopic Insights into the Influence of Filling Carbon Nanotubes with Atomic Nanowires for Photophysical and Photochemical Applications
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ACS Applied Nano Materials

Cite this: ACS Appl. Nano Mater. 2023, 6, 4, 2883–2893
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https://doi.org/10.1021/acsanm.2c05266
Published February 8, 2023

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Abstract

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Studying the optical performance of carbon nanotubes (CNTs) filled with guest materials can reveal the fundamental photochemical nature of ultrathin one-dimensional (1D) nanosystems, which are attractive for applications including photocatalysis. Here, we report comprehensive spectroscopic studies of how infiltrated HgTe nanowires (NWs) alter the optical properties of small-diameter (dt < 1 nm) single-walled carbon nanotubes (SWCNTs) in different environments: isolated in solution, suspended in a gelatin matrix, and heavily bundled in network-like thin films. Temperature-dependent Raman and photoluminescence measurements revealed that the HgTe NW filling can alter the stiffness of SWCNTs and therefore modify their vibrational and optical modes. Results from optical absorption and X-ray photoelectron spectroscopy demonstrated that the semiconducting HgTe NWs did not provide substantial charge transfer to or from the SWCNTs. Transient absorption spectroscopy further highlighted that the filling-induced nanotube distortion can alter the temporal evolution of excitons and their transient spectra. In contrast to previous studies on functionalized CNTs, where electronic or chemical doping often drove changes to the optical spectra, we highlight structural distortion as playing an important role.

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Introduction

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Following the first reports of filling carbon nanotubes (CNTs) with guest materials 3 decades ago, (1) there has been huge interest in the creation of extremely thin one-dimensional (1D) hybrid materials such as CNTs filled with molecules, (2−6) other nanotubes, (7−9) nanowires (NWs) (10−13) or nanoclusters. One prominent emerging application is the use of CNTs and nanotube heterostructures in photocatalysis, where filled or functionalized nanotubes can boost the rate of photocatalytic redox reactions that remove pollutants, perform CO2 reduction, or produce hydrogen from water. (14−16) For such applications, knowledge of the electronic and optical properties of the nanocomposite is vital, in particular because it has reported that the infiltrated material can significantly modify the electronic nature of the outer nanotubes. (17−20) For example, filling with Te can enhance the charge-carrying capacity of boron nitride nanotubes, (12) growing copper halide nanocrystals inside CNTs can lead to the creation of new carbon-copper energy levels, (21) and filling with alkane can significantly enhance the tunability of the optical performance of CNTs. (22) Further, hybrid nanotube materials,including heterostructures with BN and MoS2 and other nanotubes, exhibit unique properties such as unconventional Raman signatures, distinct phase transitions, and interesting charge-transfer processes between their constituents. (17−20,23,24) Tremendous developments in liquid-phase separation techniques have enabled the purification of not only the “host” material, such as single-walled carbon nanotubes (SWCNTs), (25−28) but also nanotube heterostructures based on their metallicity or electronic properties. (29,30) Nanotube heterostructures are also attractive components for nanoelectronics, where they can act as functional thermoelectric, photovoltaic, or conductive elements. In order to enable applications of nanotube heterostructures in photocatalysis, often in the solution phase, and nanoelectronics, where thin film geometries are more relevant, it is important to investigate how these composites behave when embedded in different environments.
The optical and electronic properties of SWCNTs can be understood to a large degree based on the electronic properties of graphene, after accounting for the helical and rotational symmetries of the nanotube (31) and many-body interactions. (32) For the lowest two excitonic transitions of semiconducting SWCNTs, S11 and S22, the many-body correction is relatively small, (32) and hence tight-binding models can accurately describe the influence of structural distortion on the excitonic transition energies. (33) For example, previous studies discovered an excitonic energy shift of SWCNTs in response to temperature and phase changes of the suspension medium. (34,35) It was shown that the observed experimental shifts were clearly dependent on the nanotube chiral angle and family type, (32) with the dominant changes in optical absorption originating from uniaxial deformation. Recently, a similar evolution of the SWCNT spectra after filling with alkane molecules was observed and assumed to be the result of a change in strain along the nanotube radial direction. (20) However, comprehensive analyses on the distortion of the SWCNT structure by spectroscopic characterizations are hindered by several factors such as doping effects (21,36) and the variation in the dielectric constant (37) of the filling.
Here we report an investigation of the optoelectronic properties of SWCNTs filled with HgTe NWs using a variety of spectroscopic probes. HgTe NWs provided an attractive candidate to explore the impact of nanotube distortion because of their high filling fraction, as well as the sufficiently small level of electronic charge transfer from filling to/from the SWCNTs, making it easier to determine how their optical properties varied following structural changes. Filled semiconducting SWCNTs, with predominantly small nanotubes (dt < 1 nm), were chosen for this study: because they exhibit strong excitonic absorption and emission spectra, they are more attractive than metallic nanotubes for nanoscale optoelectronic devices. The optical properties were examined for different CNT chiralities and with different dielectric environments: isolated in solution, in a polymer matrix, or in large bundles in a thin film. On the basis of temperature-dependent photoluminescence (PL) and Raman characterizations, the presence of HgTe NWs was found to alter the excitonic and vibrational energies of the encapsulating SWCNTs in a way that depended on their chirality. In transient absorption (TA) pump–probe spectroscopy, (13) the recombination rate of the transient exciton population was altered by HgTe NW infiltration. It was found that SWCNT species belonging to different semiconducting families [i.e. (6,5) and (7,5)] displayed opposite changes in their TA spectra, indicating the prominent effect of nanotube structure distortion following pump-induced thermal heating.

Results and Discussion

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Nanostructure and Composition

SWCNT samples were prepared with and without infiltrated HgTe NWs in different dielectric environments, as shown in Figure 1a: solution phase, gelatin-embedded, and thin film. The gelatin-embedded material was prepared by adding a gelatin solution to the sodium dodecyl sulfate (SDS)-mediated SWCNT solution (mgelatin:mSWCNT:mwater = 1:2:10) and then drop-casting the mixed solution onto the quartz substrate. The SWCNT thin-film network was prepared based on vacuum filtration using a cellulose acetate membrane followed by transfer of the film onto the quartz substrate.

Figure 1

Figure 1. (a) Schematic diagram to depict the methods of preparing SWCNT samples in different existing states. (b) Left: ADF-STEM images of the HgTe NW-filled semiconducting SWCNTs. Green and violet arrows mark the one-atom-thick zigzag NWs and wider NWs observed from the ADF-STEM image. Middle: Experimental (top) and simulated (bottom) bright-field high-resolution TEM images of two SWCNTs filled by zigzag atomic NWs. Right: Structure model of zigzag atomic NW-filled (7,6) SWCNTs. (c) UV–vis–NIR absorption spectra of SWCNT samples in different states. The dashed curve is the rescaled absorption spectrum of a blank gelatin film. The inset shows the absorption spectra of the vacuum-filtered thin films at higher energies, which revealed the π-plasma feature.

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The atomic structure of HgTe-filled semiconducting SWCNTs was studied by annular-dark-field scanning transmission electron microscopy (ADF-STEM) and high-resolution transmission electron microscopy (TEM) imaging (shown in Figure 1b). Electron microscopy images evidenced that HgTe can be successfully infiltrated into narrow nanotubes (dt < 1 nm), forming a dominant phase of zigzag-type atomic NWs with an averaged Te–Te (Hg–Hg) separation of ∼0.52 nm and a Te–Hg–Te bond angle of 110°. The scanning electron microscopy (SEM) image and atomic force microscopy (AFM) topography of vacuum-filtered SWCNT films are shown in Figures S1 and S2.
The UV–vis–near-infrared (NIR) spectra of SWCNT samples in different environments (vacuum-filtered thin film, solution state, and gelatin film) with and without HgTe infiltration are shown in Figure 1c. HgTe-infiltrated samples (solid purple lines) had absorption spectra similar to those of unfilled samples (blue dashed lines), while the morphology of the nanotubes created more significant changes. The excitonic absorption lines of thin-film-state SWCNTs (top) were markedly red-shifted and broadened compared to those of isolated solution-state (middle) and gelatin-embedded (bottom) samples. The significant nanotube bundling of SWCNTs in the vacuum-filtered film results in strong changes in the excitonic properties, such as band renormalization (a different dielectric environment) altering the excitonic energies, while ultrafast tube–tube energy transfer within bundles increases the dephasing rate, (38) broadening the excitonic lines (most clearly seen for the S11 and S22 peaks). Stronger UV absorption in the gelatin-embedded samples arose from the gelatin matrix (long-dashed line).
X-ray photoelectron spectroscopy (XPS) of the NW-filled SWCNTs is shown in Figure 2a. The reported valences of Te in crystals/alloyed compounds include Te(2−), Te(0), and Te(4+). (39−41) On the basis of their binding energy separation, we assigned the Te peaks to a stronger Te(4+) component, with a weaker contribution from Te(0)/Te(2−). (39,41) In the Hg 4f core-level spectrum, two peaks related to Hg were assigned to the split 4f7/2 and 4f5/2 levels (Figure 2a). The position and shape of the Hg 4f7/2 peak allows the Hg(2+) or Hg(0) valence states to be distinguished. (42,43) Here, the Hg 4f7/2 peak can be fit by a single Gaussian peak with a central binding energy of 100.43 eV, suggesting that Hg(2+) ions were detected by XPS. Via charge balance, the Te element in HgTe NWs would then be Te(2−). The assignment of this smaller doublet in the Te 4f region is further corroborated by the composition ratio between the total Hg 4f intensity and the smaller doublet of the Te 4f region of 1:1.06. We suggest that the prominent Te(4+) feature results from residual surface oxides on extraneous material grown outside the nanotubes, such as Te4+O42–. The Si 2p signal, which partially overlaps with the Hg 4f signal, originates from the carbon tape used to secure the sample.

Figure 2

Figure 2. (a) XPS Hg 4f (top) and Te 3d (bottom) spectra of the vacuum-filtered HgTe-filled semiconducting SWCNT thin films. (b) THz conductivity of vacuum-filtered SWCNT films (points) and simulated values based on the surface plasmon model (lines). The dotted, dashed, and dot-dashed curves, shown offset at the bottom of figure, are the three plasma oscillators contributing to the simulated conductivity spectrum of a HgTe-filled SWCNT film (blue solid curve). The plasma resonance frequency for each oscillator is denoted in the figure. (c) PLE contour map of the HgTe-filled gelatin-embedded SWCNT film. Black and white dots represent the interband energy values obtained based on the empirical model in ref (44) and the experimental energy values of these SWCNTs in solution. The orange diamond marks an assigned phonon sideband feature of (7,5). (d) Excitonic energy shifts of various (n,m) species as a result of changes in the surrounding medium, ΔEii. (e) Excitonic energy shifts induced by changes in the temperature, ΔEii = Eii,298 K – Eii,80 K.

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Conductivity

We studied the conductivity of vacuum-filtered SWCNT films by characterizing their far-infrared transmittance via terahertz time-domain spectroscopy (THz-TDS). The experimental transmittance was converted into alternating-current conductivity, the real part of which is shown in Figure 2b (points), based on the thin-film approximation. (45) The conductivity for both unfilled and HgTe-filled SWCNT films increased toward higher frequencies. Previous results, obtained in the mid-infrared using Fourier transform infrared (FTIR) spectroscopy on similar films placed on Si substrates, indicated the presence of a strong plasmon mode around 7–9 THz for the unfilled and filled samples. (13) Here, additional conductivity in the spectrum of the HgTe-filled SWCNT film can be seen in the 0.5–2.0 THz range. We interpreted the spectra using the axial plasmon model for a number of different plasmon frequencies, corresponding to different SWCNT lengths or bundle numbers, (46) creating the solid curves in Figure 2b. The model was expressed as follows:
σ(ω)=∑j=1niσp,jωγp,jω2−ωp,j2+iωγp,j
(1)
where ωp,j is the plasmon resonance frequency, σp,j is the plasmon conductivity at the resonance frequency (ω = ωp,j), and γp,j is the plasmon scattering rate for each of the n oscillators. A small number of plasmon oscillators can model the physical situation, which has a continuous distribution of CNT bundle lengths.
The fit for the unfilled sample required a single plasmon oscillator located at a relatively high frequency (solid gray line in Figure 2b). In contrast, the extra conductivity in the spectrum of the HgTe-filled SWCNT film from 0.5 to 2.0 THz was modeled by additional plasmon resonances at 1.1 and 2.4 THz (dotted and dashed lines). Consistent with our previous results from FTIR spectroscopy, (13) HgTe filling resulted in both a broadening (the damping rate increased from 70 to 90 ps–1 from unfilled to filled) and a blueshifting (the central frequency increased from 7 to 9 THz) of the stronger, IR plasmon resonance peak.
The small extra optical conductivity of the HgTe@SWCNT composite may imply a weak doping of the SWCNTs after infiltration, or it may result from subtle differences in film morphology in comparison to the reference film. We return to a discussion of electronic doping later in the paper.

PL Spectroscopy

Photoluminescence excitation (PLE) maps of unfilled and HgTe-filled gelatin-embedded SWCNT films at room temperature and 80 K are shown in Figures 2c and S3–S5, where excitonic emission from different (n,m) SWCNTs are evident. We calculated and assigned the excitonic S11 and S22 transitions using the theoretical interband transition energies introduced by a previous study: (44)
Eii=a[pdt+bpdtlog⁡cp/dt]+βpdt2cos⁡3θ+γdt
(2)
where p = 1 or 2 depending on the transition order, a, b, and c are all constants, and dt and θ are the diameter and chiral angle of the SWCNT. In this model, the quantum confinement of the 2D electronic structure of graphene is represented by the linear term ap/dt, the logarithmic term accounts for many-body electron interactions, the chiral angle-dependent term corrects for a variation with the SWCNT chirality, and γ/dt is linked to the exciton binding energy. We found that the experimental S11 and S22 energies of most (n,m) species in the gelatin-embedded SWCNTs could be simulated using the parameters a = 1.049 eV, b = 0.456 nm, c = 0.795 nm–1, β1 = 0.05 nm2 [mod(n–m) = 1]/–0.07 nm2 [mod(n–m) = 2)], β2 = −0.19 (mod = 1)/0.14 (mod = 2), and γ = 0.305 eV. By increasing the strength of the log term from c = 0.795 to 0.814 nm–1, the recalculated energies for these small-diameter (n,m) [e.g., (6,5), (7,5), (7,6), and (10,2)] were found to be closer to the experimental energies of those in a solution state (Figure S6), indicating that encapsulation in gelatin can potentially modify the many-body Coulomb interactions within the SWCNTs.
The difference between the experimentally determined Eii of solution-state and gelatin-embedded SWCNT samples, ΔEii = Eii,gelatin – Eii,solution, is shown in Figure 2d. For the unfilled SWCNTs (dashed lines), both S11 and S22 are at higher energies in solution than in gelatin (ΔEii ≃ −20 meV) as a result of the gelatin matrix changing the many-body interactions, whereas for the filled SWCNTs (solid lines), ΔEii ≃ −10 meV. Interestingly, for the HgTe-filled SWCNTs, ΔE11 displays an observable dependence on the CNT family, with the mod 1 family having a smaller ΔE11 than mod 2 SWCNTs. Thus, when filled, changing the outer dielectric environment alters the excitonic energies in a way that depends on the CNT family. To investigate further, ΔE11 was plotted against nanotube diameter dt (Figure 2d) and against cos 3θ and sin 3θ (Figure S7), where θ is the chiral angle of the SWCNT. No clear dependence of ΔEii on dt or θ was discernible, suggesting that multiple parameters in eq 2 are altered simultaneously.
We now suggest a physical mechanism by which the optical properties of SWCNTs depend on the environment. In a SDS solution, a SWCNT is believed to have an outer micellar coating with a configuration depending on various factors, such as the SWCNT chirality or metallicity, (25,47) the pH of the medium, (48) and the lengths of SWCNTs. (49) Presumably, immobilizing the micelle-coated SWCNTs in a gelatin matrix can result in a change in the configuration of surfactant coatings by, for example, replacing SDS at the surface with gelatin molecules. This can modify the local dielectric constant felt by charges in the SWCNTs and lead to a change in their excitonic and optical properties.
We used a temperature-dependent PLE study to further examine the excitonic properties of unfilled versus HgTe-filled SWCNTs. The temperature-induced Eii shifts (ΔEii = Eii,298 K – Eii,80 K) for four different (n,m) species in unfilled and HgTe-filled gelatin-embedded film samples are shown in Figure 2e. Taking into account a significant difference in the thermal expansion constant between the SWCNT and gelatin matrix, the observed energy shift upon cooling should result from a change of the uniaxial strain on SWCNTs, (50−52) which is expressed as
ΔEii=(−1)i+1(−1)k+13t0(1+v)ϵcos⁡3θ
(3)
where i is the transition order, k is the mod index of a SWCNT, which equals mod(n–m,3), and t0 ≃ 3 eV. ϵ is the uniaxial strain, while v ∼ 0.2 is the Poisson ratio. The experimental shifts in Figure 2e fall on the line ΔE11 = −ΔE22 (solid green line), matching the expectation from eq 3.
In previous studies, it was reported that infiltration of the CNTs by molecules can expand or distort the nanotube circumference, hence shifting the interband transition energy due to increased radial strain. (20,53,54) The energy shift with radial strain σ varies with chiral angle θ according to (33)
ΔEii=(−1)i+1(−1)k+13t0σsin⁡3θ
(4)
This relationship predicts a strong family-type dependence of the energy shift. In our previous work on solution-state HgTe-infiltrated SWCNTs, a dependence of filling-induced ΔEii on k was seen for solution-state SWCNTs, (13) with a generally larger ΔEii for type 1 SWCNTs such as (7,5) and (10,2) than on type 2 SWCNTs such as (8,4) and (6,5). However, no such effect can be seen in the gelatin-embedded samples (Figure 2c), suggesting that the morphology (gelatin matrix) may prevent or offset substantial radial strain.

Raman Spectroscopy

As an alternative method to investigate how infiltration alters strain and the optical properties, we turned to resonant Raman spectroscopy. (55) The temperature-dependent Raman spectra of vacuum-filtered SWCNT films under two different excitation wavelengths (660 and 532 nm) are shown in Figures 3 and S8–S15. The discovered radial breathing mode (RBM) signatures (Figure 3a–d) revealed that different (n,m) species were resonantly excited under the two wavelengths. Most of the Raman modes were found to display a decreased intensity, increased line-width broadening, and lower Raman shifts with a rise in temperature. Such a spectral evolution at higher temperatures has been reported in a previous work where both semiconducting and metallic SWCNTs were investigated (56) and can be attributed to the faster dephasing of the excitonic state at elevated temperatures.

Figure 3

Figure 3. Temperature-dependent Raman spectra of the vacuum-filtered unfilled (a and b) and HgTe-filled (c and d) thin films in the RBM regime under an excitation wavelength of 660 nm (a and c) and 532 nm (b and d). The dashed vertical lines in panels c and d mark the central frequencies of the room-temperature RBM peaks for the corresponding unfilled SWCNT samples. Changes in the Raman shifts of different Raman modes for the unfilled (open circles) and HgTe-filled (solid circles) SWCNT film samples against temperature under 660 nm (e) and 532 nm (f) excitation. The dotted and solid straight lines are linear fits to the data points. The extracted thermal constants (dωmode/dT) and their errors based on a linear fit to the data are presented in the graphs.

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The spectral shifts of the various Raman modes with temperature were then studied (Figure 3e,f). The observed softening of both the radial and tangential frequencies at higher temperature has been previously attributed to a weakening of the intertubular and intratubular bonds. (55) The experimental data points were well fitted by straight lines, allowing the temperature coefficient (dωmode/dT) to be determined. The temperature coefficients measured were chirality-dependent: for instance, the RBM of unfilled (7,5) SWCNTs (seen under 660 nm) had dωmode/dT = −1.04 ± 0.05 m–1 K–1, while unfilled (8,4) SWCNTs had dωmode/dT = −0.71 ± 0.04 m–1K–1. The G modes also had larger temperature coefficients for unfilled (7,5) and (7,6) SWCNTs (Figure 3e) than for unfilled (8,4) and (6,5) SWCNTs (Figure 3f).
Under 660 and 532 nm excitations, a notable reduction in the temperature coefficients after HgTe filling was found for the RBM modes (Figure 3e,f). The temperature coefficients for the G+ mode also reduced after filling under 660 nm excitation [i.e. probing predominantly (7,5) SWCNTs ], while under 532 nm excitation [i.e. probing (8,4) and (6,5) SWCNTs], the G modes appeared to be unaffected. For SWCNTs forming into thick bundles, as in the thin-film morphology in this Raman study, an increased temperature is thought to weaken both the intratube bonds and the intertube van der Waals forces, redshifting the RBM and G modes, whereas thermal expansion in the radial direction contributes less than 10% of the redshift. (55) Hence, one hypothesis consistent with the above experimental results is that, while HgTe NW filling may marginally increase the diameter of the SWCNT, accounting for the lower RBM frequencies after filling, the lower temperature coefficient may result from modified force constants for the intratube or intertube bonds. (55)
Additional Raman modes were observed at Raman shifts higher than those for the G modes (Figures S13 and S15), namely, the two double-resonance phonon modes, denoted as M and iTOLA (in-plane transverse optical, longitudinal acoustic). The M mode is the predicted overtone of the out-of-plane transverse optical (oTO) mode, while iTOLA is a combination of one phonon from the in-plane TO branch and one phonon from the longitudinal acoustic (LA) branch. (57) The M modes determined under 660 nm excitation could be deconvoluted into a lower-frequency component (∼1720 cm–1, referred to as the M– branch) and a higher-frequency component (∼1755 cm–1, referred to as the M+ branch), meaning that a phonon scattering process satisfying both |q| ≈ 0 and |q| ≈ 2|k| was achieved. (57) The iTOLA modes detected under 532 nm excitation (Figure S15) displayed a higher asymmetric nature than those under 660 nm excitation (Figure S13) and were deconvoluted into a lower-frequency line (at ∼1920 cm–1) and one or few higher-frequency component(s), which can be explained by the emergence of additional vibrational modes such as LOLA (longitudinal optical, longitudinal acoustic). (58) A change in the temperature coefficients of the D, M, and iTOLA modes was also detected after HgTe filling, showing a tendency (Figures S12 and S14) consistent with the above results on the G and RBM modes. Alongside the results from temperature-dependent PL, the experimental evidence is that strain due to NW filling can impact different types of vibrational motion (i.e., radial breathing and C–C bond stretching and bending), modifying the intratube and intertube bond strengths.

Electron Doping

In this section, we return to the discussion of possible electron transfer between the HgTe and SWCNTs, which might dope the SWCNTs, which was discussed above with regard to the THz conductivity spectra. The slight redshifts of RBM and the G, D, and M bands of the vacuum-filtered HgTe-filled SWCNT films under certain excitation wavelengths [660 nm (Figures 3a and S10 and S13) and 561 nm (Figures S16 and S17) excitation] can be interpreted as a weak electronic doping of the SWCNT but may also result from a mechanical effect created by HgTe infiltration, as discussed in the previous section. Hence, in this section, we discuss electronic doping in more detail.
The level of electron doping can be estimated from the decrease in the integrated area of the excitonic absorption peak. (59,60) In the UV–vis–NIR absorption spectra of solution-state and gelatin-embedded SWCNT samples, the two main S11 absorption peaks, assigned to the excitonic features of (7,5) and (7,6)/(8,4) SWCNTs, were suppressed in strength after HgTe filling (Figure 1c). This suggests that filling caused a small depopulation of the valence band (p-type doping) or a small population increase in the conduction band (n-type doping). The electronic influence of HgTe NW infiltration was further investigated via XPS, which has been widely used to study doping in other 1D NW/SWCNT composites. For example, XPS and ultraviolet photoelectron spectroscopy (UPS) showed that metal halides (CuX (21) and AgX, (36) where X = Cl, Br, or I) and metals (Ni (61)) are strong dopants, as evidenced via an observably blue-shifted sp2 C peak (graphene lattice π peak), attributed to charge transfer between NW and CNT. Here, for the SWCNTs filled with HgTe NWs, in contrast, there was nearly no spectral shift of the sp2 C 1s peak (Figure S18), which is consistent with there being little substantial doping created by the HgTe NWs. Thus, we conclude that methods that are sensitive to both structural or electronic doping changes (e.g., Raman and PL) are dominated by structural changes in this case, whereas techniques such as THz spectroscopy, which probe electronic properties only, can better assess subtle changes in conductivity.

Ultrafast Dynamics

Finally, TA spectroscopy was carried out across the NIR and visible ranges on samples suspended in solutions or in gelatin matrices, in order to study the relaxation dynamics of the photoinduced product (excitons and free carriers) and to act as a more sensitive probe of the excitonic states. In our previous work, we investigated exciton dynamics in the early time regime (<5 ps), where exciton–exciton annihilation (Auger) effects were prominent. (13) In this work, we examined data obtained at later pump–probe delay times (up to 100 ps) in order to explore slower dynamical processes and investigated the influence of the surrounding environment. From the TA characteristics of solution-state SWCNTs with a pump photon energy of 3.542 eV (350 nm), close to the S33 resonance, two main ground-state bleach (GSB) peaks were evident at ∼1.25 and ∼1.2 eV (Figure 4a,b). These can be assigned to the S11 absorption features of (6,5) and (7,5) SWCNTs, respectively, while the shoulder at ∼1.18 eV on the lower-energy side of (7,5) can be attributed to S11 from a small amount of (10,2) SWCNTs. The transient spectrum was modified by HgTe filling, as witnessed by the dashed lines in Figure 4a,b (contours of constant ΔOD) and by the differing optical density change reported in Figure 4g.

Figure 4

Figure 4. (a–f) Heatmaps of the differential transmission signals [ΔOD(t)/ΔOD0] of the solution-state SWCNTs against probe energies (1.15–1.35 eV) and pump–probe delays at various pump energies. (g–i) Corresponding spectra averaged over a time window from 0.4 to 1.5 ps. The dashed curves were added in parts a–f to indicate the spectral profiles of the GSB features. The vertical lines and arrows in parts g and i indicate the spectral shifts of GSB for (7,5) and (6,5), respectively.

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We then obtained TA spectra and dynamics for different excitation conditions: at 2.44 eV (508 nm) and 1.984 eV (625 nm), in the e–h pair continuum of the S22 interband transitions for all of the SWCNTs studied (Figure 4c). The discovered GSB signatures had different relative weights under different pump energies: the absorption change from (6,5) SWCNTs (around 1.25 eV) was relatively weaker at 2.44 eV excitation and was stronger for the other pump wavelengths. Interestingly, the sign of the photoinduced shifts in S11 seems to change with the SWCNT family type: type 1 (7,5) and (10,2) displayed a red-shifted S11 peak (Figure 4g), while type 2 (6,5) showed a blueshift (Figure 4i). Because the pump fluences for measurements on the unfilled and HgTe-filled SWCNTs were the same and the molarities of the nanotubes in the unfilled and HgTe-filled samples were similar (see the Supporting Information for an estimation of the molar concentrations), the shifts should not be a result of biexciton or trion generation on the S11 manifold. (62,63) An increase in the local dielectric constant felt by SWCNTs has been reported to lead to a decreased exciton binding energy, (64) which would create a blueshift in S11, as found after HgTe infiltration for (6,5) SWCNTs but not for (7,5). Instead, the family-dependent shifts observed in the TA spectra may result from a photothermal effect. Referring back to Figure 2e and eq 3, an elevated lattice temperature in thermal equilibrium can create either blueshifts or redshifts in S11, where ΔE11 changes sign with k, i.e., is opposite for (7,5) and (6,5) SWCNTs. Pulsed excitation injects energy into the electronic system, which rapidly transfers to the lattice via electron–phonon coupling. This can occur rapidly via Auger processes in HgTe-filled SWCNTs, as we previously reported. (13) Here, however, we suggest that the family-dependent shifts in the excitonic energies seen in the experiment may be linked to modified uniaxial or radial strain coefficients in line with eqs 3 and 4. A schematic of the processes involved is presented in Figure 5a.

Figure 5

Figure 5. (a) Schematic showing that the suppression of in-plane (stretching and bending) and out-of-plane (radial breathing) vibrational movements due to SWCNT filling results in an increased stiffness of the nanotube upon photoexcitation. The proposed mechanism is based on the assumption that lattice vibrations along both the in-plane and out-of-plane directions are unrestricted in the liquid environment. (b) TA spectra of SWCNTs in different states averaged over a time window from 0.4 to 0.9 ps with different pump energies. All spectra were normalized to the minimum values of the corresponding GSB feature located at around 1.2 eV. Representative semilog and log–log TA kinetic curves of gelatin-embedded SWCNT films at a pump energy of (c and d) 3.542 eV and (e and f) 2.44 eV. The straight lines in panels d and f are the power-law fits [n(t) ∝tα] to the experimental data.

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Compared to the TA spectra of solution-state SWCNTs, those of gelatin-embedded SWCNTs were smeared out further in energy (Figures 5b and S19), potentially as a result of inhomogeneity and/or faster dephasing caused by variations in the local dielectric function. One important consequence of this may be that the S11 excitonic states could become more similar to higher-order states (e.g., S33 and S44), where the photoexcited e–h pairs behave more like free charge carriers.
Turning now to consider S11 excitonic recombination processes, we report in Figure 5c–f the decay dynamics for (7,5) in the gelatin-embedded films under pump energies of 3.54 eV (Figure 5c,d) and 2.44 eV (Figure 5e,f). On the semilog axes (Figure 5c,e), a prominent nonlinearity in the decay curves can be observed at early pump–probe delays (<5 ps), indicating the occurrence of Auger-type nonradiative relaxation, as expected at the excitation fluences used (over 1000 excitons per nanotube). This feature is further evident in the log–log axes (Figure 5d) as the steeper slope at early times. A log–log scale further allows the reactivity of the excitons to be investigated. (65) At the pump energy of 3.542 eV, excitons displayed a remarkable two-stage behavior because the dynamic curves for both unfilled and HgTe-filled SWCNTs followed a power-law relationship [n(t) ∝ tα] with α ≃ −0.6 before 2 ps and α ≃ −0.3 afterward (Figure 5d). This is an indicator that the excitons were more reactive in the few picoseconds after excitation due to a large amount of them being generated on a single nanotube at the applied pump fluence. (65,66) The results also suggest that the slow lifetime component relates to diffusive excitonic motion, where excitons migrate along the SWCNTs before recombining. In contrast, when the S11 excitons were generated with lower pump photon energy (2.44 eV), the reaction kinetics were less strongly time-dependent but showed a clearer variation with HgTe filling (Figure 5f). The larger exponent (α ≃ −0.6) for HgTe-filled SWCNTs illustrates boosted recombination pathways, which may result from coupling between the electronic or vibrational systems of the NWs and SWCNTs.

Conclusion

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In this paper, we presented a detailed spectroscopic characterization of zigzag atomic chains of HgTe encapsulated within narrow-diameter SWCNTs. We studied the influence of HgTe infiltration on the optical properties of SWCNT films in a variety of different environments (solution state, embedded in gelatin, and thin film). By comparing the PL features of gelatin-embedded nanotube samples at room temperature (300 K) and at 80 K, we showed that NW filling reduces the temperature-dependent shifts for various (n,m) species, suggesting a suppressed uniaxial strain constant. Subsequent temperature-dependent Raman measurements provided evidence that the thermal coefficients of various vibrational modes (e.g., RBM mode, G mode, and double-resonance modes such as the M and iTOLA modes) decreased as a result of NW infiltration, indicating that strain can affect both in-plane and out-of-plane (radial breathing) C–C vibrational motion. These results suggest that filling with NWs alters the intratube bond stiffness of the SWCNTs, as previously reported, as well as the intertube interactions within SWCNT bundles. Here, the lower thermal coefficient after filling demonstrated that the C–C bond length changed less rapidly with temperature. This may be useful in photocatalytic applications because the electronic properties and reaction rates may be less temperature-dependent. Changes to the intertube interactions are particularly important for conductive thin-film applications of SWCNT heterostructures: if the filling modifies the intertube van der Waals interactions, the bundle density and conductivity of thin-film networks can change. Indeed, the modified THz conductivity spectra suggest that this may have occurred.
Characterizations based on optical absorption in a wide range of wavelengths, and via XPS, demonstrated that HgTe NWs had a weak doping effect on the surrounding nanotubes. This offers evidence that structural distortion, rather than direct electronic interactions (e.g., doping), controlled the spectroscopic performance of small-sized SWCNTs after infiltration. TA spectroscopy revealed a temporal evolution of exciton features depending on the SWCNT type, which features the effect of nanotube distortion under light-induced heating.
Our experimental studies demonstrate that infiltration by atomic NWs can be a novel way to control both the equilibrium-state and time-dependent properties of CNTs. This could pave the way for a comprehensive understanding of the interactions within ultrathin 1D heterostructures. In particular, for applications involving semiconducting nanotubes (e.g., photocatalysis, transistors, and photovoltaics), our results identify the important role of the filling in modifying the SWCNT structure and tube–tube interactions.

Methods

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Materials

SWCNTs produced by CoMoCAT (ref no. 775533) were used as the raw CNT product. Sodium dodecyl sulfate (SDS; ACS reagent, ≥99.0%, Sigma-Aldrich) was used as the surfactant to produce a micelle coating and isolate CNTs. Mercury telluride (HgTe; 99%, Alfa Aesar) was used as the filling material. Hydrogels made from a cross-linked copolymer of allyldextran and N,N′-methylenebis(acrylamide) (Sephacryl S-200, GE Healthcare) were applied for the gel column chromotography experiment. Gelatin was applied as the polymer matrix for preparing gelatin-embedded SWCNT films.

Synthesis and Purification of Materials

Processes of SWCNT filling and purification based on the gel column chromatography method were detailed in our previous work. (13) The extracted semiconducting SWCNTs with a dominance of small nanotubes (dt < 1 nm) were chosen for the study here. Gelatin-embedded SWCNT films were made by drop-casting a mixture of gelatin, SWCNT dispersion, and deionized water (mass ratio mgelatin:mSWCNT:mwater = 1:2:10) onto the quartz substrate and leaving it to dry at room temperature for 12 h. SWCNT thin films were prepared based on the vacuum filtration method using the cellulose filter membrane (0.2 μm, Merck). For optical measurements, the films were transferred onto the quartz substrate with membranes dissolved by acetone.

SEM and STEM Imaging

SEM imaging was conducted based on a Zeiss Gemini microscope, which was operated under an extremely low electron voltage (0.3 kV) to avoid the charging effect. TEM and ADF-STEM were conducted based on a doubly corrected JEOL ARM200F microscope under an acceleration voltage of 200 kV and were demonstrated not to cause serious damage to the C structure. For the ADF-STEM measurement, the pixel dwell time was set to 20 μs and the chosen camera length was 8 cm, corresponding to a collection semiangle of 35–180 mrad. During ADF-STEM characterizations, the beam current density on the fluorescence screen was about 0.2 pA cm–1. The SWCNT samples were loaded onto the lacey TEM grid by drop-casting. The TEM grids were baked in an vacuum oven at 100–150 °C for 12 h prior to characterization in order to remove contaminants such as hydrocarbon molecules. Image analyses were carried out in the Gatan Microscopy Suite (GMS) software.

AFM Imaging

The sample height and morphology of the material were studied by a Bruker Dimension Icon atomic force microscope. Measurements were carried out under peak force tapping mode at a tapping rate of 2 kHz, with an Al-coated SiN cantilever (tip radius = 2–12 nm, spring constant = 40 N m–1, resonant frequency = ∼70 kHz, length = ∼115 μm, and width = ∼25 μm) applied as the probe.

XPS

To carry out XPS measurements on the vacuum-filtered SWCNT thin films, they were attached to electrically conductive carbon tape and mounted onto a sample bar, before being loaded into a Kratos Axis Ultra DLD spectrometer. The load lock was pumped to below 1 × 10–6 mbar before sample transfer to the analysis chamber. After sample transfer, the analysis chamber had a base pressure below 1 × 10–10 mbar. XPS was performed with the sample illuminated using a monochromated Al Kα X-ray source (hν = 1486.7 eV). The measurements were conducted at room temperature and at a takeoff angle of 90° with respect to the surface parallel. The core-level spectra were recorded using a pass energy of 20 eV (resolution of approximately 0.4 eV), from an analysis area of 300 mm × 700 mm. The work function and binding energy scale of the spectrometer were calibrated using the Fermi edge and 3d5/2 peak recorded from a polycrystalline Ag sample prior to commencement of the experiments. The data were analyzed in the CasaXPS package using Shirley backgrounds and mixed Gaussian–Lorentzian (Voigt) line shapes, with asymmetry parameters where appropriate. Due to surface charging during the experiment, the samples had to be flooded with a beam of low-energy electrons in order to keep the surface from becoming positively charged. This necessitated subsequent referencing of the binding energy scale to the C–C/C–H adventitious C component at 284.6 eV. For compositional analysis, the analyzer transmission function was determined using clean metallic foils to determine the detection efficiency across the full binding energy range.

Steady-State Spectroscopy

UV–vis–NIR (260–1800 nm or 4.77–0.69 eV) and far-infrared (0.2–3 THz or 0.8–12.4 meV) absorbance of the material was characterized by a PerkinElmer Lambda1050 spectrometer and a THz-TDS setup where photoconductive antenna and ZnTe were served as the emitter and detection crystal, respectively. (67)
Raman measurements were carried out on Renishaw InVia Reflex (532 nm excitation), Horiba T64000 triple-stage (561 nm excitation), and Horiba LabRam HR Evolution (660 nm excitation) spectrometers. A small laser power was used to avoid sample heating. For the temperature-dependent Raman measurements, the sample was placed in a Linkam stage (THMS600), which was controlled by a Linkam T96 system. The stage chamber was purged with nitrogen prior to the temperature rising. The Raman signals were measured first at room temperature and then from 100 to 400 °C with an interval of 50 °C at a ramping rate of 40 °C min–1. A spectrum was acquired 2 min after the temperature reached the set value. The issue of the sample moving and defocusing during heating can be neglected because the Raman spectra were normalized to their background signal intensities afterward. All Raman modes of semiconducting SWCNT species were fitted by Lorentzian functions, while the G– peak of coexisting metallic SWCNTs was instead fitted by a Breit–Wigner–Fano (BWF) line shape (Figure S17). Optimized fits to the spectrum in the G-mode regime were obtained based on the Levenberg–Marquardt method.
PL of the solution-state and gelatin-embedded SWCNTs was characterized by a Horiba Fluorolog-3 spectrometer equipped with a xenon lamp that generated a broadband white-light beam. A single-photon-counting photomultiplier-tube detector was used to detect the fluorescence signals at NIR (850–1350 nm) wavelengths. The spectrometer corrected for variations in the lamp output automatically. Fluorescence of the solution-state and gelatin-embedded SWCNTs was collected in right-angle and front-face geometries, respectively. For the contour mapping measurement, a band-pass filter with nearly 100% transmittance between 332 and 807 nm and a NIR filter were placed after the excitation grating slit and before the emission grating slit, respectively. Low-temperature PL of the gelatin-embedded SWCNT films was characterized based on a cryostat (Oxford), which allowed the temperature to go down and be stabilized at 80 K. The excitonic energies of the SWCNTs were determined by fitting the experimental PL or PLE spectra with Gaussian functions and finding the peak energies.

TA Spectroscopy

The exciton dynamics of the SWCNT samples were examined using a TA spectrometer. Both the pump and probe beams were derived from an optical parametric amplifier (TOPAS) that was seeded with a 1 kHz, 40 fs, and 800 nm pulse generated by an amplified Ti:sapphire laser (Newport Spectra Physics Spitfire Ace PA). The pump beam was mechanically chopped at 500 Hz. Different white-light probe continuua (330–720 and 700–1100 nm) were produced from a CaF2 crystal pumped at 800 nm and a sapphire crystal pumped at 1300 nm, respectively. A set of neutral-density filters and narrow band-pass filters were placed in the beam path to avoid saturation of the detector while affording a broadband white-light supercontinuum. The pulse width/duration of the setup was 40 fs, which defined the resolution of the experiment. The acquired TA signals were chirp-corrected. To carry out measurements under both resonant and nonresonant conditions, pump wavelengths of 350, 508, and 625 nm were chosen. The pump fluences were aimed to be set to a pretty high level (>1 × 1016 photons cm–2) in order for different relaxation pathways to be examined. Under these sufficiently large pump fluences, the transient processes were believed to enter a nonlinear regime (saturation) due to the fluence-dependent quasi-elastic dephasing. (68)

Supporting Information

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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsanm.2c05266.

  • Supporting electron microscopy images and additional data from PL, XPS, Raman, and TA spectroscopies (PDF)

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Most electronic Supporting Information files are available without a subscription to ACS Web Editions. Such files may be downloaded by article for research use (if there is a public use license linked to the relevant article, that license may permit other uses). Permission may be obtained from ACS for other uses through requests via the RightsLink permission system: http://pubs.acs.org/page/copyright/permissions.html.

Author Information

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  • Corresponding Authors
  • Authors
    • Ben Breeze - Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom;  Orcidhttps://orcid.org/0000-0002-7979-9753
    • Marc Walker - Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, United Kingdom
    • Eric Faulques - Institut des Matriaux de Nantes Jean Rouxel, CNRS, University of Nantes, Nantes F-44000, France;  Orcidhttps://orcid.org/0000-0002-7761-8509
  • Notes
    The authors declare no competing financial interest.

Acknowledgments

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J.S. is indebted to the Engineering and Physical Sciences Research Council (EPSRC; Swindon, U.K.) for support from Grant EP/R019428/1, while M.W. and B.B. acknowledge financial support from the EPSRC-funded Warwick Analytical Science Centre (EP/V007688/1). The authors acknowledge use of the Warwick Centre for Ultrafast Spectroscopy Research Technology Platform (RTP) facility, the Electron Microscopy RTP, and the Spectroscopy RTP at the University of Warwick.

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    Elemental phosphorus displays an impressive no. of allotropes with highly diverse chem. and phys. properties. White phosphorus has now been filled into single-wall carbon nanotubes (SWCNTs) from the liq. and thereby stabilized against the highly exothermic reaction with atm. oxygen. The encapsulated tetraphosphorus mols. were visualized with transmission electron microscopy, but found to convert readily into chain structures inside the SWCNT "nanoreactors". The energies of the possible chain structures were detd. computationally, highlighting a delicate balance between the extent of polymn. and the SWCNT diam. Exptl., a single-stranded zig-zag chain of phosphorus atoms was obsd., which is the lowest energy structure at small confinement diams. These one-dimensional chains provide a glimpse into the very first steps of the transformation from white to red phosphorus.
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  12. 12
    Qin, J. K.; Liao, P. Y.; Si, M.; Gao, S.; Qiu, G.; Jian, J.; Wang, Q.; Zhang, S. Q.; Khin Yap, Y.; Ye, P. D.; Huang, S.; Charnas, A.; Wang, Y.; Kim, M. J.; Wu, W.; Xu, X.; Wang, H. Y.; Yang, L. Raman response and transport properties of tellurium atomic chains encapsulated in nanotubes. Nature Electronics 2020, 3, 141– 147,  DOI: 10.1038/s41928-020-0365-4
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    12
    Raman response and transport properties of tellurium atomic chains encapsulated in nanotubes
    Qin, Jing-Kai; Liao, Pai-Ying; Si, Mengwei; Gao, Shiyuan; Qiu, Gang; Jian, Jie; Wang, Qingxiao; Zhang, Si-Qi; Huang, Shouyuan; Charnas, Adam; Wang, Yixiu; Kim, Moon J.; Wu, Wenzhuo; Xu, Xianfan; Wang, Hai-Yan; Yang, Li; Khin Yap, Yoke; Ye, Peide D.
    Nature Electronics (2020), 3 (3), 141-147CODEN: NEALB3; ISSN:2520-1131. (Nature Research)
    Tellurium can form nanowires of helical at. chains. With their unique one-dimensional van der Waals structure, these nanowires are expected to show phys. and electronic properties that are remarkably different from those of bulk tellurium. Here, we show that few-chain and single-chain van der Waals tellurium nanowires can be isolated using carbon nanotube and boron nitride nanotube encapsulation. With this approach, the no. of at. chains can be controlled by the inner diam. of the nanotube. The Raman response of the structures suggests that the interaction between a single-at. tellurium chain and a carbon nanotube is weak, and that the inter-chain interaction becomes stronger as the no. of chains increases. Compared with bare tellurium nanowires on SiO2, nanowires encapsulated in boron nitride nanotubes exhibit a dramatically enhanced current-carrying capacity, with a c.d. of 1.5 × 108 A cm-2 that exceeds that of most semiconducting nanowires. We also use our tellurium nanowires encapsulated in boron nitride nanotubes to create field-effect transistors with a diam. of only 2 nm.
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  13. 13
    Hu, Z.; Breeze, B.; Kashtiban, R. J.; Sloan, J.; Lloyd-Hughes, J. Zigzag HgTe Nanowires Modify the Electron-Phonon Interaction in Chirality-Refined Single-Walled Carbon Nanotubes. ACS Nano 2022, 16, 6789– 6800,  DOI: 10.1021/acsnano.2c01647
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    13
    Zigzag HgTe Nanowires Modify the Electron-Phonon Interaction in Chirality-Refined Single-Walled Carbon Nanotubes
    Hu, Ziyi; Breeze, Ben; Kashtiban, Reza J.; Sloan, Jeremy; Lloyd-Hughes, James
    ACS Nano (2022), 16 (4), 6789-6800CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Atomically thin nanowires (NWs) can be synthesized inside single-walled carbon nanotubes (SWCNTs) and feature unique crystal structures. Here we show that HgTe nanowires formed inside small-diam. (<1 nm) SWCNTs can advantageously alter the optical and electronic properties of the SWCNTs. Metallic purifn. of the filled SWCNTs was achieved by a gel column chromatog. method, leading to an efficient extn. of the semiconducting and metallic portions with known chiralities. Electron microscopic imaging revealed that zigzag HgTe chains were the dominant NW geometry in both the semiconducting and metallic species. Equil.-state and ultrafast spectroscopy demonstrated that the coupled electron-phonon system was modified by the encapsulated HgTe NWs, in a way that varied with the chirality. For semiconducting SWCNTs with HgTe NWs, Auger relaxation processes were suppressed, leading to enhanced photoluminescence emission. In contrast, HgTe NWs enhanced the Auger relaxation rate of metallic SWCNTs and created faster phonon relaxation, providing exptl. evidence that encapsulated at. chains can suppress hot carrier effects and therefore boost electronic transport.
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    Woan, K.; Pyrgiotakis, G.; Sigmund, W. Photocatalytic Carbon-Nanotube-TiO2 Composites. Adv. Mater. 2009, 21, 2233– 2239,  DOI: 10.1002/adma.200802738
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    Photocatalytic Carbon-Nanotube-TiO2 Composites
    Woan, Karran; Pyrgiotakis, Georgios; Sigmund, Wolfgang
    Advanced Materials (Weinheim, Germany) (2009), 21 (21), 2233-2239CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. The literature and advances in photocatalysis based on the combination of titania (TiO2) and carbon nanotubes is presented. The semiconductor basis for photocatalysis is introduced for anatase and rutile. Furthermore, the proposed mechanisms of catalytic enhancement resulting from the pairing of the titania semiconductor with either metallic, semiconducting, or defect-rich carbon nanotubes (CNT) is discussed. Differences are apparent for the mixts. and chem. bonded CNT-TiO2 composites. The article then highlights the recent advances in the synthesis techniques for these composites and their photocatalytic reactions with org., inorg., and biol. agents. Finally, various applications and challenges for these composite materials are reported.
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    González-Muñoz, D.; Martín-Somer, A.; Strobl, K.; Cabrera, S.; De Pablo, P. J.; Díaz-Tendero, S.; Blanco, M.; Alemán, J. Enhancing Visible-Light Photocatalysis via Endohedral Functionalization of Single-Walled Carbon Nanotubes with Organic Dyes. ACS Appl. Mater. Interfaces 2021, 13, 24877– 24886,  DOI: 10.1021/acsami.1c04679
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    15
    Enhancing Visible-Light Photocatalysis via Endohedral Functionalization of Single-Walled Carbon Nanotubes with Organic Dyes
    Gonzalez-Munoz, Daniel; Martin-Somer, Ana; Strobl, Klara; Cabrera, Silvia; De Pablo, Pedro J.; Diaz-Tendero, Sergio; Blanco, Matias; Aleman, Jose
    ACS Applied Materials & Interfaces (2021), 13 (21), 24877-24886CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
    The encapsulation of an org. dye, 10-phenylphenothiazine (PTH), in the inner cavity of single-walled carbon nanotubes (SWNTs) as a breaking heterogenization strategy is presented. The PTH@oSWNT material was microscopically and spectroscopically characterized, showing intense photoemission when illuminated with visible light at the nanoscale. Thus, PTH@oSWNT was employed as a heterogeneous photocatalyst in single electron transfer dehalogenation reactions under visible light irradn. The material showed an enhanced photocatalytic activity, achieving turnover nos. as high as 3200, with complete recyclability and stability for more than eight cycles. Computational calcns. confirm that electronic communication between both partners is established because, upon illumination, an electron of the excited PTH is transferred from the π system of the mol. to the delocalized π-cloud of the SWNT, thus justifying the enhanced photocatalytic activity.
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    Zhang, J.; Dai, M.; Zhang, S.; Dai, M.; Zhang, P.; Wang, S.; He, Z. Recent Progress on Carbon-Nanotube-Based Materials for Photocatalytic Applications: A Review. Solar RRL 2022, 6, 2200243,  DOI: 10.1002/solr.202200243
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    16
    Recent Progress on Carbon-Nanotube-Based Materials for Photocatalytic Applications: A Review
    Zhang, Jing; Dai, Mingchong; Zhang, Shijie; Dai, Meng; Zhang, Peng; Wang, Shuguang; He, Zuoli
    Solar RRL (2022), 6 (9), 2200243CODEN: SRORAW; ISSN:2367-198X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. As one of the most outstanding allotropes of carbon assembled with a cylindrical nanostructure, carbon nanotubes (CNTs) have attracted extensive attention in the areas of material science and engineering due to their unique structural characteristics and physicochem. properties. Very recently, versatile hierarchical CNT-based photocatalysts are of considerable interest in current research and applications ranging from fuel generation to environmental purifn. Therefore, it is necessary to summarize the CNT-based photocatalysts to provide essential refs. for the continuous research study. In this review, the different design strategies and flexible functionalizations for prototype construction are described and their typical research, esp. the structure-related or electronic-effected mechanism in the photocatalytic reaction of pollutants degrdation, water splitting, and CO2 redn. overviewed. Finally, the various aspects of CNT-based photocatalysts are discussed for future developments in compd. applications.
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  17. 17
    Spencer, J. H.; Nesbitt, J. M.; Trewhitt, H.; Kashtiban, R. J.; Bell, G.; Ivanov, V. G.; Faulques, E.; Sloan, J.; Smith, D. C. Raman Spectroscopy of Optical Transitions and Vibrational Energies of 1 nm HgTe Extreme Nanowires within Single Walled Carbon Nanotubes. ACS Nano 2014, 8, 9044– 9052,  DOI: 10.1021/nn5023632
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    17
    Raman Spectroscopy of Optical Transitions and Vibrational Energies of ∼1 nm HgTe Extreme Nanowires within Single Walled Carbon Nanotubes
    Spencer, Joseph H.; Nesbitt, John M.; Trewhitt, Harrison; Kashtiban, Reza J.; Bell, Gavin; Ivanov, Victor G.; Faulques, Eric; Sloan, Jeremy; Smith, David C.
    ACS Nano (2014), 8 (9), 9044-9052CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    This paper presents a resonance Raman spectroscopy study of ∼1 nm diam. HgTe nanowires formed inside single walled carbon nanotubes by melt infiltration. Raman spectra have been measured for ensembles of bundled filled tubes, produced using tubes from two sep. sources, for excitation photon energies in the ranges 3.39-2.61 and 1.82-1.26 eV for Raman shifts down to ∼25 cm-1. We also present HRTEM characterization of the tubes and the results of DFT calcns. of the phonon and electronic dispersion relations, and the optical absorption spectrum based upon the obsd. structure of the HgTe nanowires. All of the evidence supports the hypothesis that the obsd. Raman features are not attributable to single walled carbon nanotubes, i.e., peaks due to radial breathing mode phonons, but are due to the HgTe nanowires. The obsd. addnl. features are due to four distinct phonons, with energies 47, 51, 94, and 115 cm-1, resp., plus their overtones and combinations. All of these modes have strong photon energy resonances that maximize at around 1.76 eV energy with respect to incident laser.
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  18. 18
    Shi, L.; Rohringer, P.; Suenaga, K.; Niimi, Y.; Kotakoski, J.; Meyer, J. C.; Peterlik, H.; Wanko, M.; Cahangirov, S.; Rubio, A.; Lapin, Z. J.; Novotny, L.; Ayala, P.; Pichler, T. Confined linear carbon chains as a route to bulk carbyne. Nat. Mater. 2016, 15, 634– 639,  DOI: 10.1038/nmat4617
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    Confined linear carbon chains as a route to bulk carbyne
    Shi, Lei; Rohringer, Philip; Suenaga, Kazu; Niimi, Yoshiko; Kotakoski, Jani; Meyer, Jannik C.; Peterlik, Herwig; Wanko, Marius; Cahangirov, Seymur; Rubio, Angel; Lapin, Zachary J.; Novotny, Lukas; Ayala, Paola; Pichler, Thomas
    Nature Materials (2016), 15 (6), 634-639CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
    Strong chem. activity and extreme instability in ambient conditions characterize carbyne, an infinite sp1 hybridized carbon chain. As a result, much less has been explored about carbyne as compared to other carbon allotropes such as fullerenes, nanotubes and graphene. Although end-capping groups can be used to stabilize carbon chains, length limitations are still a barrier for prodn., and even more so for application. We report a method for the bulk prodn. of long acetylenic linear carbon chains protected by thin double-walled carbon nanotubes. The synthesis of very long arrangements is confirmed by a combination of transmission electron microscopy, X-ray diffraction and (near-field) resonance Raman spectroscopy. Our results establish a route for the bulk prodn. of exceptionally long and stable chains composed of more than 6,000 carbon atoms, representing an elegant forerunner towards the final goal of carbyne's bulk prodn.
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    Chambard, R.; Moreno-López, J. C.; Hermet, P.; Sato, Y.; Suenaga, K.; Pichler, T.; Jousselme, B.; Aznar, R.; Bantignies, J. L.; Izard, N.; Alvarez, L. Tuning of photoluminescence intensity and Fermi level position of individual single-walled carbon nanotubes by molecule confinement. Carbon 2022, 186, 423– 430,  DOI: 10.1016/j.carbon.2021.09.072
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    19
    Tuning of photoluminescence intensity and Fermi level position of individual single-walled carbon nanotubes by molecule confinement
    Chambard, Romain; Moreno-Lopez, Juan Carlos; Hermet, Patrick; Sato, Yuta; Suenaga, Kazu; Pichler, Thomas; Jousselme, Bruno; Aznar, Raymond; Bantignies, Jean-Louis; Izard, Nicolas; Alvarez, Laurent
    Carbon (2022), 186 (), 423-430CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Photoluminescence of single-walled carbon nanotubes is monitored at the individual scale by mol. encapsulation into their hollow core. Depending on the electronic character (electron donor or acceptor) of the confined mol., enhancement or quenching of the photoluminescence intensity is demonstrated. This behavior is assigned to a charge transfer, evidenced by the shift of the Raman G-band, and a correlated Fermi level shift shown by photoemission expts. Our exptl. results are supported by DFT calcns. A consistent picture of the phys. interactions taking place in the hybrid systems and their effects on the optical and electronic properties is given. Our results indicate that the electron affinity or ionization potential of the encapsulated mols. and the diam. of the nanotube are relevant parameters to tune the light emission properties of the hybrid systems at the nanoscale.
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    Qu, H.; Rayabharam, A.; Wu, X.; Wang, P.; Li, Y.; Fagan, J.; Aluru, N. R.; Wang, Y. H. Selective filling of n-hexane in a tight nanopore. Nat. Commun. 2021, 12, 1– 8,  DOI: 10.1038/s41467-020-20587-1
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    Eliseev, A. A.; Yashina, L. V.; Verbitskiy, N. I.; Brzhezinskaya, M. M.; Kharlamova, M. V.; Chernysheva, M. V.; Lukashin, A. V.; Kiselev, N. A.; Kumskov, A. S.; Freitag, B.; Generalov, A. V.; Vinogradov, A. S.; Zubavichus, Y. V.; Kleimenov, E.; Nachtegaal, M. Interaction between single walled carbon nanotube and 1D crystal in CuX@SWCNT (X = Cl, Br, I) nanostructures. Carbon 2012, 50, 4021– 4039,  DOI: 10.1016/j.carbon.2012.04.046
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    21
    Interaction between single walled carbon nanotube and 1D crystal in CuX@SWCNT (X = Cl, Br, I) nanostructures
    Eliseev, A. A.; Yashina, L. V.; Verbitskiy, N. I.; Brzhezinskaya, M. M.; Kharlamova, M. V.; Chernysheva, M. V.; Lukashin, A. V.; Kiselev, N. A.; Kumskov, A. S.; Freitag, B.; Generalov, A. V.; Vinogradov, A. S.; Zubavichus, Y. V.; Kleimenov, E.; Nachtegaal, M.
    Carbon (2012), 50 (11), 4021-4039CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    CuX@SWCNT (X = Cl, Br, I) nanostructures were prepd. by capillary filling of 1.4-1.6 nm single-walled carbon nanotubes (SWCNT) with copper halides. The structure of CuX@SWCNT (X = Cl, Br, I) represents a distorted two-layer hcp of halogen atoms arranged along the SWCNT. The EXAFS and the high angle angular dark field (HAADF) HRTEM data indicate that Cu is partially coordinated by C. According to the optical absorption, valence band photoemission spectroscopy and work function measurements, a Fermi level (FL) downshift as compared with the initial value for the nanotubes and a corresponding charge transfer from the nanotubes to the 1D crystals is obsd. for CuX@SWCNT nanostructures. The FL shift increases in the sequence CuI < CuBr < CuCl due to an increase of the electron affinity for the halogen atoms. The XPS data confirm the acceptor effect of copper halides and indicate that metallic and semiconducting nanotubes behave differently. Raman spectroscopy performed under electrochem. charging allowed estn. of the value of charge transfer between the nanotube walls and the intercalated 1D crystal. The X-ray absorption and emission spectra for carbon and copper thresholds revealed a new energy level composed of the carbon 2pz and copper 3d-orbitals. This indicates the Cu-C bonding, which in line with the structural HAADF HRTEM and EXAFS data.
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    Campo, J.; Piao, Y.; Lam, S.; Stafford, C. M.; Streit, J. K.; Simpson, J. R.; Hight Walker, A. R.; Fagan, J. A. Enhancing single-wall carbon nanotube properties through controlled endohedral filling. Nanoscale Horizons 2016, 1, 317– 324,  DOI: 10.1039/C6NH00062B
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    Enhancing single-wall carbon nanotube properties through controlled endohedral filling
    Campo, J.; Piao, Y.; Lam, S.; Stafford, C. M.; Streit, J. K.; Simpson, J. R.; Hight Walker, A. R.; Fagan, J. A.
    Nanoscale Horizons (2016), 1 (4), 317-324CODEN: NHAOAW; ISSN:2055-6764. (Royal Society of Chemistry)
    Chem. control of the endohedral vol. of single-wall carbon nanotubes (SWCNTs) via liq.-phase filling is established to be a facile strategy to controllably modify properties of SWCNTs in manners significant for processing and proposed applications. Encapsulation of over 20 different compds. with distinct chem. structures, functionalities, and effects is demonstrated in SWCNTs of multiple diam. ranges, with the ability to fill the endohedral vol. based on the availability of the core vol. and compatibility of the mol.'s size with the cross-section of the nanotube's cavity. Through exclusion of ingested water and selection of the endohedral chem. environment, significant improvements to the optical properties of dispersed SWCNTs such as narrowed optical transition linewidths and enhanced fluorescence intensities are obsd. Examples of tailoring modified properties towards applications or improved processing by endohedral passivation are discussed.
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    Burdanova, M. G.; Kashtiban, R. J.; Zheng, Y.; Xiang, R.; Chiashi, S.; Woolley, J. M.; Staniforth, M.; Sakamoto-Rablah, E.; Xie, X.; Broome, M.; Sloan, J.; Anisimov, A.; Kauppinen, E. I.; Maruyama, S.; Lloyd-Hughes, J. Ultrafast optoelectronic processes in 1d radial van der Waals heterostructures: Carbon, boron nitride, and MoS2 nanotubes with coexisting excitons and highly mobile charges. Nano Lett. 2020, 20, 3560– 3567,  DOI: 10.1021/acs.nanolett.0c00504
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    Ultrafast Optoelectronic Processes in 1D Radial van der Waals Heterostructures: Carbon, Boron Nitride, and MoS2 Nanotubes with Coexisting Excitons and Highly Mobile Charges
    Burdanova, Maria G.; Kashtiban, Reza J.; Zheng, Yongjia; Xiang, Rong; Chiashi, Shohei; Woolley, Jack Matthew; Staniforth, Michael; Sakamoto-Rablah, Emily; Xie, Xue; Broome, Matthew; Sloan, Jeremy; Anisimov, Anton; Kauppinen, Esko I.; Maruyama, Shigeo; Lloyd-Hughes, James
    Nano Letters (2020), 20 (5), 3560-3567CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Heterostructures built from 2D, atomically thin crystals are bound by the van der Waals force and exhibit unique optoelectronic properties. Here, we report the structure, compn. and optoelectronic properties of 1D van der Waals heterostructures comprising carbon nanotubes wrapped by atomically thin nanotubes of boron nitride and molybdenum disulfide (MoS2). The high quality of the composite was directly made evident on the at. scale by transmission electron microscopy, and on the macroscopic scale by a study of the heterostructure's equil. and ultrafast optoelectronics. Ultrafast pump-probe spectroscopy across the visible and terahertz frequency ranges identified that, in the MoS2 nanotubes, excitons coexisted with a prominent population of free charges. The electron mobility was comparable to that found in high-quality atomically thin crystals. The high mobility of the MoS2 nanotubes highlights the potential of 1D van der Waals heterostructures for nanoscale optoelectronic devices.
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    Burdanova, M. G.; Liu, M.; Staniforth, M.; Zheng, Y.; Xiang, R.; Chiashi, S.; Anisimov, A.; Kauppinen, E. I.; Maruyama, S.; Lloyd-Hughes, J. Intertube Excitonic Coupling in Nanotube Van der Waals Heterostructures. Adv. Funct. Mater. 2022, 32, 2104969,  DOI: 10.1002/adfm.202104969
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    Intertube Excitonic Coupling in Nanotube Van der Waals Heterostructures
    Burdanova, Maria G.; Liu, Ming; Staniforth, Michael; Zheng, Yongjia; Xiang, Rong; Chiashi, Shohei; Anisimov, Anton; Kauppinen, Esko I.; Maruyama, Shigeo; Lloyd-Hughes, James
    Advanced Functional Materials (2022), 32 (11), 2104969CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
    Strong intertube excitonic coupling is demonstrated in 1D van der Waals heterostructures by examg. the ultrafast response of radial C/BN/MoS2 core/shell/skin nanotubes to femtosecond IR light pulses. Remarkably, IR excitation of excitons in the semiconducting carbon nanotubes (CNTs) creates a prominent excitonic response in the visible range from the MoS2 skin, even with IR photons at energies well below the bandgap of MoS2. Via classical analogies and a quantum model of the light-matter interaction these findings are assigned to intertube excitonic correlations. Dipole-dipole Coulomb interactions in the coherent regime produce intertube biexcitons, which persist for tens of femtoseconds, while on longer timescales (>100 ps) hole tunneling-from the CNT core, through the BN tunnel barrier, to the MoS2 skin-creates intertube excitons. Charge transfer and dipole-dipole interactions thus play prominent roles on different timescales, and establish new possibilities for the multi-functional use of these new nanoscale coaxial cables.
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    Liu, H.; Nishide, D.; Tanaka, T.; Kataura, H. Large-scale single-chirality separation of single-wall carbon nanotubes by simple gel chromatography. Nat. Commun. 2011, 2, 1– 8,  DOI: 10.1038/ncomms1313
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    An optimized small molecule inhibitor cocktail supports long-term maintenance of human embryonic stem cells
    Tsutsui, Hideaki; Valamehr, Bahram; Hindoyan, Antreas; Qiao, Rong; Ding, Xianting; Guo, Shuling; Witte, Owen N.; Liu, Xin; Ho, Chih-Ming; Wu, Hong
    Nature Communications (2011), 2 (Jan.), 1-8, 8 pp.CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    A major challenge in stem cell-mediated regenerative medicine is the development of defined culture systems for the maintenance of clin.-grade human embryonic stem (hES) cells. Here, we identify, using a feedback system control scheme, a unique combination of three small mol. inhibitors that enables the maintenance of hES cells on a fibronectin-coated surface through single cell passaging. After 20 passages, the undifferentiated state of the hES cells was confirmed by OCT4, SSEA4 and NANOG expressions, whereas their pluripotent potential and genetic integrity were demonstrated by teratoma formation and normal karyotype, resp. Our study attests to the power of the feedback system control scheme to quickly pinpoint optimal conditions for desired biol. activities, and provides a chem. defined, scalable and single cell passaging culture system for hES cells.
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    Tu, X.; Manohar, S.; Jagota, A.; Zheng, M. DNA sequence motifs for structure-specific recognition and separation of carbon nanotubes. Nature 2009, 460, 250– 253,  DOI: 10.1038/nature08116
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    DNA sequence motifs for structure-specific recognition and separation of carbon nanotubes
    Tu, Xiaomin; Manohar, Suresh; Jagota, Anand; Zheng, Ming
    Nature (London, United Kingdom) (2009), 460 (7252), 250-253CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
    Single-walled carbon nanotubes (SWNTs) are a family of mols. that have the same cylindrical shape but different chiralities. Many fundamental studies and technol. applications of SWNTs require a population of tubes with identical chirality that current syntheses cannot provide. The SWNT sorting problem - i.e., sepn. of a synthetic mixt. of tubes into individual single-chirality components - has attracted considerable attention in recent years. Intense efforts so far have focused largely on, and resulted in solns. for, a weaker version of the sorting problem: metal/semiconductor sepn. A systematic and general method to purify each and every single-chirality species of the same electronic type from the synthetic mixt. of SWNTs is highly desirable, but the task proved to be insurmountable to date. Here the authors report such a method, which allows purifn. of all 12 major single-chirality semiconducting species from a synthetic mixt., with sufficient yield for both fundamental studies and application development. The authors have designed an effective search of a DNA library of ∼1060 in size, and have identified >20 short DNA sequences, each of which recognizes and enables chromatog. purifn. of a particular nanotube species from the synthetic mixt. Recognition sequences exhibit a periodic purine-pyrimidines pattern, which can undergo hydrogen-bonding to form a two-dimensional sheet, and fold selectively on nanotubes into a well-ordered three-dimensional barrel. Probably the ordered two-dimensional sheet and three-dimensional barrel provide the structural basis for the obsd. DNA recognition of SWNTs.
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    Ghosh, S.; Bachilo, S. M.; Weisman, R. B. Advanced sorting of single-walled carbon nanotubes by nonlinear density-gradient ultracentrifugation. Nat. Nanotechnol. 2010, 5, 443– 450,  DOI: 10.1038/nnano.2010.68
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    Advanced sorting of single-walled carbon nanotubes by nonlinear density-gradient ultracentrifugation
    Ghosh, Saunab; Bachilo, Sergei M.; Weisman, R. Bruce
    Nature Nanotechnology (2010), 5 (6), 443-450CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
    Existing methods for growing single-walled carbon nanotubes produce samples with a range of structures and electronic properties, but many potential applications require pure nanotube samples. D.-gradient ultracentrifugation has recently emerged as a technique for sorting as-grown mixts. of single-walled nanotubes into their distinct (n,m) structural forms, but to date this approach is limited to samples contg. only a small no. of nanotube structures, and has often required repeated d.-gradient ultracentrifugation processing. Here, it is reported that the use of tailored nonlinear d. gradients can significantly improve d.-gradient ultracentrifugation sepns. It is shown that highly polydisperse samples of single-walled nanotubes grown by the HiPco method are readily sorted in a single step to give fractions enriched in any of ten different (n,m) species. Furthermore, minor variants of the method allow sepn. of the mirror-image isomers (enantiomers) of seven (n,m) species. Optimization of this approach was aided by the development of instrumentation that spectroscopically maps nanotube contents inside undisturbed centrifuge tubes.
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    Arnold, M. S.; Green, A. A.; Hulvat, J. F.; Stupp, S. I.; Hersam, M. C. Sorting carbon nanotubes by electronic structure using density differentiation. Nat. Nanotechnol. 2006, 1, 60– 65,  DOI: 10.1038/nnano.2006.52
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    Sorting carbon nanotubes by electronic structure using density differentiation
    Arnold, Michael S.; Green, Alexander A.; Hulvat, James F.; Stupp, Samuel I.; Hersam, Mark C.
    Nature Nanotechnology (2006), 1 (1), 60-65CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
    The heterogeneity of as-synthesized single-walled carbon nanotubes (SWNTs) precludes their widespread application in electronics, optics and sensing. The authors report on the sorting of carbon nanotubes by diam., bandgap and electronic type using structure-discriminating surfactants to engineer subtle differences in their buoyant densities. Using the scalable technique of d.-gradient ultracentrifugation, the authors have isolated narrow distributions of SWNTs in which >97% are within a 0.02-nm-diam. range. Also, using competing mixts. of surfactants, the authors produced bulk quantities of SWNTs of predominantly a single electronic type. These materials were used to fabricate thin-film elec. devices of networked SWNTs characterized by either metallic or semiconducting behavior.
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    Fagan, J. A.; Huh, J. Y.; Simpson, J. R.; Blackburn, J. L.; Holt, J. M.; Larsen, B. A.; Walker, A. R. Separation of empty and water-filled single-wall carbon nanotubes. ACS Nano 2011, 5, 3943– 3953,  DOI: 10.1021/nn200458t
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    Separation of Empty and Water-Filled Single-Wall Carbon Nanotubes
    Fagan, Jeffrey A.; Huh, Ji Yeon; Simpson, Jeffrey R.; Blackburn, Jeffrey L.; Holt, Josh M.; Larsen, Brian A.; Hight Walker, Angela R.
    ACS Nano (2011), 5 (5), 3943-3953CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    The sepn. of empty and water-filled laser ablation and elec. arc synthesized nanotubes is reported. Centrifugation of these large-diam. nanotubes dispersed with sodium deoxycholate using specific conditions produces isolated bands of empty and water-filled nanotubes without significant diam. selection. This sepn. is consistent across multiple nanotube populations dispersed from different source soots. Detailed spectroscopic characterization of the resulting empty and filled fractions reveals that water filling leads to systematic changes to the optical and vibrational properties. Also, sequential sepn. of the resolved fractions using cosurfactants and d. gradient ultracentrifugation reveals that water filling strongly influences the optimal conditions for metallic and semiconducting sepn.
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  30. 30
    Yang, X.; Liu, T.; Li, R.; Yang, X.; Lyu, M.; Fang, L.; Zhang, L.; Wang, K.; Zhu, A.; Zhang, L.; Qiu, C.; Zhang, Y. Z.; Wang, X.; Peng, L. M.; Yang, F.; Li, Y. Host-Guest Molecular Interaction Enabled Separation of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes. J. Am. Chem. Soc. 2021, 143, 10120– 10130,  DOI: 10.1021/jacs.1c02245
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    Host-Guest Molecular Interaction Enabled Separation of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes
    Yang, Xusheng; Liu, Tianhui; Li, Ruoming; Yang, Xiaoxin; Min, Lyu; Fang, Li; Zhang, Lei; Wang, Kun; Zhu, Anquan; Zhang, Luyao; Qiu, Chenguang; Zhang, Yuan-Zhu; Wang, Xiao; Peng, Lian-Mao; Yang, Feng; Li, Yan
    Journal of the American Chemical Society (2021), 143 (27), 10120-10130CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
    Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a diam. of around 1.0-1.5 nm, which present bandgaps comparable to silicon, are highly desired for electronic applications. Therefore, the prepn. of s-SWCNTs of such diams. has been attracting great attention. The inner surface of SWCNTs has a suitable curvature and large contacting area, which is attractive in host-guest chem. triggered by electron transfer. Here we reported a strategy of host-guest mol. interaction between SWCNTs and inner clusters with designed size, thus selectively sepg. s-SWCNTs of expected diams. When polyoxometalate clusters of ~ 1 nm in size were filled in the inner cavities of SWCNTs, s-SWCNTs with diams. concd. at ~ 1.3-1.4 nm were selectively extd. with the purity of ~ 98% by a com. available polyfluorene deriv. The field-effect transistors built from the sorted s-SWCNTs showed a typical behavior of semiconductors. The sorting mechanisms assocd. with size-dependent electron transfer from nanotubes to inner polyoxometalate were revealed by the spectroscopic and in situ electron microscopic evidence as well as the theor. calcn. The polyoxometalates with designable size and redox property enable the flexible regulation of interaction between the nanotubes and the clusters, thus tuning the diam. of sorted s-SWCNTs. The present sorting strategy is simple and should be generally feasible in other SWCNT sorting techniques, bringing both great easiness in dispersant design and improved selectivity.
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    White, C. T.; Robertson, D. H.; Mintmire, J. W. Helical and rotational symmetries of nanoscale graphitic tubules. Phys. Rev. B 1993, 47, 5485,  DOI: 10.1103/PhysRevB.47.5485
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    Helical and rotational symmetries of nanoscale graphitic tubules
    White, C. T.; Robertson, D. H.; Mintmire, J. W.
    Physical Review B: Condensed Matter and Materials Physics (1993), 47 (9), 5485-8CODEN: PRBMDO; ISSN:0163-1829.
    The authors show how all extended graphitic tubules constructed by rolling up a single graphite sheet can be defined in terms of their helical and rotational symmetries. Specification of these symmetries is practically mandatory in all but the simplest calcns. of tubule properties as a function of radius and structure. The authors also report results of a tight-binding study implemented by using these symmetries. Independent of their helicity the larger-diam., moderate-band-gap semiconducting tubules all have band gaps given approx. by Eg = |V0|(d0/RT), where RT is the tubule radius and V0 is the hopping matrix element between nearest-neighboring 2p orbitals oriented normal to the tubule surface and centered on C atoms sepd. by a distance d0 along this surface. All tubules constructed by rolling up the graphite sheet can be labeled in a fashion familiar in the description of helical chain polymers with translational symmetry.
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    Sato, K.; Saito, R.; Jiang, J.; Dresselhaus, G.; Dresselhaus, M. S. Discontinuity in the family pattern of single-wall carbon nanotubes. Physical Review B - Condensed Matter and Materials Physics 2007, 76, 195446,  DOI: 10.1103/PhysRevB.76.195446
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    Discontinuity in the family pattern of single-wall carbon nanotubes
    Sato, K.; Saito, R.; Jiang, J.; Dresselhaus, G.; Dresselhaus, M. S.
    Physical Review B: Condensed Matter and Materials Physics (2007), 76 (19), 195446/1-195446/7CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    The higher lying bright exciton energies (EM11,ES33,ES44,EM22,ES55,ES66,EM33) of single-wall C nanotubes are calcd. by solving the Bethe-Salpeter equation within an extended tight binding method. For smaller diam. nanotubes, some higher Eii excitonic states are missing. In particular, some Eii's on the 1-dimensional Brillouin zone (cutting line) are no longer relevant to the formation of excitons and are skipped in listing the order of the Eii values. Thus the family patterns show some discontinuities in k space and this effect should be observable in Raman G' band spectroscopy. The higher exciton energies ES33 and ES44 have a large chirality dependence due to many body effects, since the self-energy becomes larger than the binding energy. Thus the chirality dependence of the higher Eii comes not only from a single particle energy but also from many-body effects.
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    Yang, L.; Han, J. Electronic structure of deformed carbon nanotubes. Phys. Rev. Lett. 2000, 85, 154,  DOI: 10.1103/PhysRevLett.85.154
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    Electronic Structure of Deformed Carbon Nanotubes
    Yang, Liu; Han, Jie
    Physical Review Letters (2000), 85 (1), 154-157CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Electronic structure of deformed carbon nanotubes varies widely depending on their chirality and deformation mode. We present a framework to analyze these variations by quantifying the dispersion relation and d. of states. The theory is based on the Huckel tight-binding model and confirmed by four orbital tight-binding simulations of nanotubes under stretching, compression, torsion, and bending. It unriddles and unifies previous band gap studies and predicts the shifting, merging, and splitting of Van Hove singularities in the d. of state, and the zigzag pattern of band gap change with strains. Possible applications to nanotube devices and spectroscopy research are also presented.
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    Arnold, K.; Lebedkin, S.; Kiowski, O.; Hennrich, F.; Kappes, M. M. Matrix-Imposed Stress-Induced Shifts in the Photoluminescence of Single-Walled Carbon Nanotubes at Low Temperatures. Nano Lett. 2004, 4, 2349– 2354,  DOI: 10.1021/nl048630c
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    Matrix-Imposed Stress-Induced Shifts in the Photoluminescence of Single-Walled Carbon Nanotubes at Low Temperatures
    Arnold, Katharina; Lebedkin, Sergei; Kiowski, Oliver; Hennrich, Frank; Kappes, Manfred M.
    Nano Letters (2004), 4 (12), 2349-2354CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Photoluminescence spectra of H2O-surfactant dispersions of semiconducting single-walled C nanotubes (SWNTs) show large shifts of interband transition energies upon freezing and cooling the dispersions to 16 K. This is accompanied by an increase of the emission intensities up to ∼10 times in the presence of poly(vinylpyrrolidone). The shifts develop mainly in the temp. interval of ∼100-240 K and are reversible by cycling the temp. Two groups of nanotubes classified by the value of (n-m) mod 3, where n,m are structure indexes, demonstrate opposite shifts, the largest ones from nanotubes with small chiral angles. The exptl. data agree well with calcns. of Yang et al. [Phys. Rev. B 1999, 60, 13874] for SWNTs under axial compression and indicate that large stresses of up to ∼5 GPa are generated in individual nanotubes by thermal contraction of the ice matrix.
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    Karaiskaj, D.; Engtrakul, C.; McDonald, T.; Heben, M. J.; Mascarenhas, A. Intrinsic and extrinsic effects in the temperature-dependent photoluminescence of semiconducting carbon nanotubes. Phys. Rev. Lett. 2006, 96, 106805,  DOI: 10.1103/PhysRevLett.96.106805
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    Intrinsic and Extrinsic Effects in the Temperature-Dependent Photoluminescence of Semiconducting Carbon Nanotubes
    Karaiskaj, D.; Engtrakul, C.; McDonald, T.; Heben, M. J.; Mascarenhas, A.
    Physical Review Letters (2006), 96 (10), 106805/1-106805/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    The temp. dependence of the band gap of semiconducting C nanotubes was measured for ten different nanotube species. The unprecedented effectiveness in avoiding the effect of external strain, or any other effects originating from the surrounding environment, lead to an accurate measurement of the band gap temp. dependence, giving fundamental insight into the nanotube electron-phonon interaction. Small but reproducible energy shifts of the emission lines with temp. were obsd., showing a moderate chirality dependence, well in agreement with recent theor. calcns. In addn. to the energy shift, a substantial narrowing of the emission lines was also obsd. The removal of the temp. shift of the band gap allows the precise measurement of the effect of external strain on C nanotubes in different environments.
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    Eliseev, A. A.; Yashina, L. V.; Brzhezinskaya, M. M.; Chernysheva, M. V.; Kharlamova, M. V.; Verbitsky, N. I.; Lukashin, A. V.; Kiselev, N. A.; Kumskov, A. S.; Zakalyuhin, R. M.; Hutchison, J. L.; Freitag, B.; Vinogradov, A. S. Structure and electronic properties of AgX (X = Cl, Br, I)-intercalated single-walled carbon nanotubes. Carbon 2010, 48, 2708– 2721,  DOI: 10.1016/j.carbon.2010.02.037
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    Structure and electronic properties of AgX (X = Cl, Br, I)-intercalated single-walled carbon nanotubes
    Eliseev, A. A.; Yashina, L. V.; Brzhezinskaya, M. M.; Chernysheva, M. V.; Kharlamova, M. V.; Verbitsky, N. I.; Lukashin, A. V.; Kiselev, N. A.; Kumskov, A. S.; Zakalyuhin, R. M.; Hutchison, J. L.; Freitag, B.; Vinogradov, A. S.
    Carbon (2010), 48 (10), 2708-2721CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    One-dimensional Ag halide crystals were grown within single-walled nanotube (SWCNT) channels from the melt using a molten media method. Atomic structures of the AgX@SWCNT hybrids are proposed based on high-resoln. TEM images. AgCl intercalation results in amorphous filling of the SWCNT channels. 1-dimensional AgBr and AgI crystals intercalated into 1.34 nm SWCNTs possess the structure of a two-layer hcp. of halogen atoms arranged laterally with respect to the SWCNT axis. Electronic properties and chem. bonding in AgX@SWNTs were studied by high-resoln. x-ray photoelectron and near edge X-ray absorption fine structure spectroscopy (BESSY, Germany), optical absorption and Raman spectroscopy. Optical absorption spectroscopy indicates disappearance of E11S transitions between van-Hove singularities, which is caused by an effective electron exchange between AgX and the SWCNT. C 1s x-ray absorption spectra indicate a new empty level (S1) induced by charge transfer. Multi-component structure of photoemission spectra can be explained both by the variation of the work function of AgX@SWCNT hybrids and local interactions between halogen ions and C atoms. Raman spectroscopy performed under electrochem. charging clearly and directly demonstrated the acceptor behavior of AgX with respect to SWCNTs. Based on a whole dataset, a self-consistent picture of the AgX-SWCNT interactions is derived.
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    Campo, J.; Cambré, S.; Botka, B.; Obrzut, J.; Wenseleers, W.; Fagan, J. A. Optical Property Tuning of Single-Wall Carbon Nanotubes by Endohedral Encapsulation of a Wide Variety of Dielectric Molecules. ACS Nano 2021, 15, 2301– 2317,  DOI: 10.1021/acsnano.0c08352
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    Optical Property Tuning of Single-Wall Carbon Nanotubes by Endohedral Encapsulation of a Wide Variety of Dielectric Molecules
    Campo, Jochen; Cambre, Sofie; Botka, Bea; Obrzut, Jan; Wenseleers, Wim; Fagan, Jeffrey A.
    ACS Nano (2021), 15 (2), 2301-2317CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    Specific and tunable modification to the optical properties of single-wall carbon nanotubes (SWCNTs) is demonstrated through direct encapsulation into the nanotube interior of guest mols. with widely varying static dielec. consts. Filled through simple ingestion of the guest mol., each SWCNT population is demonstrated to display a robust modification to absorbance, fluorescence, and Raman spectra. Over 30 distinct compds., covering static dielec. consts. from 1.8 to 109, are inserted in large diam. SWCNTs (d = 1.104-1.524 nm) and more than 10 compds. in small diam. SWCNTs (d = 0.747-1.153 nm), demonstrating that the general effect of filler dielec. on the nanotube optical properties is a monotonic energy redn. (red-shifting) of the optical transitions with increased magnitude of the dielec. const. Systematic fitting of the two-dimensional fluorescence-excitation and Raman spectra addnl. enables detn. of the crit. filling diam. for each mol. and distinguishing of overall trends from specific guest-host interactions. Comparisons to predictions from existing theory are presented, and specific guest mol./SWCNT chirality combinations that disobey the general trend and theory are identified. A general increase of the fluorescence intensity and line narrowing is obsd. for low dielec. consts., with long linear alkane filled SWCNTs exhibiting emission intensities approaching those of empty SWCNTs. These results demonstrate an exploitable modulation in the optical properties of SWCNTs and provide a foundation for examg. higher-order effects, such as due to nonbulk-like mol. stacking, in host-guest interactions in well-controlled nanopore size materials.
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    Mehlenbacher, R. D.; McDonough, T. J.; Grechko, M.; Wu, M.-Y.; Arnold, M. S.; Zanni, M. T. Energy transfer pathways in semiconducting carbon nanotubes revealed using two-dimensional white-light spectroscopy. Nat. Commun. 2015, 6, 6732,  DOI: 10.1038/ncomms7732
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    Energy transfer pathways in semiconducting carbon nanotubes revealed using two-dimensional white-light spectroscopy
    Mehlenbacher, Randy D.; McDonough, Thomas J.; Grechko, Maksim; Wu, Meng-Yin; Arnold, Michael S.; Zanni, Martin T.
    Nature Communications (2015), 6 (), 6732CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
    Thin film networks of highly purified semiconducting carbon nanotubes (CNTs) are being explored for energy harvesting and optoelectronic devices because of their exceptional transport and optical properties. The nanotubes in these films are in close contact, which permits energy to flow through the films, although the pathways and mechanisms for energy transfer are largely unknown. Here we use a broadband continuum to collect femtosecond two-dimensional white-light spectra. The continuum spans 500 to 1,300 nm, resolving energy transfer between all combinations of bandgap (S1) and higher (S2) transitions. We observe ultrafast energy redistribution on the S2 states, non-Forster energy transfer on the S1 states and anti-correlated energy levels. The two-dimensional spectra reveal competing pathways for energy transfer, with S2 excitons taking routes depending on the bandgap sepn., whereas S1 excitons relax independent of the bandgap. These observations provide a basis for understanding and ultimately controlling the photophysics of energy flow in CNT-based devices.
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    Christie, A. B.; Sutherland, I.; Walls, J. M. Studies of the composition, ion-induced reduction and preferential sputtering of anodic oxide films on Hg0.8Cd0.2Te by XPS. Surf. Sci. 1983, 135, 225– 242,  DOI: 10.1016/0039-6028(83)90220-0
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    Studies of the composition, ion-induced reduction and preferential sputtering of anodic oxide films on mercury cadmium telluride (Hg0.8Cd0.2Te) by XPS
    Christie, A. B.; Sutherland, I.; Walls, J. M.
    Surface Science (1983), 135 (1-3), 225-42CODEN: SUSCAS; ISSN:0039-6028.
    Angle-resolved studies of anodic oxide films on Hg0.8Cd0.2Te (CMT), and on Cd and Te bulk oxides, by XPS revealed the formation of a discrete altered overlayer, contg. reduced Te (Te0) species, following inert gas ion bombardment. In the presence of Cd2+ species, recombination occurs yielding a Te2- (telluride) species, in the form of CdTe. Only Te2- formation is obsd. on ion-induced redn. of CdTeO3, whereas there is no evidence for significant Te2- formation on either TeO2 or anodic oxides on CMT, reflecting the low Cd content of these latter 2 oxides. In addn., preferential cation sputtering leads to a homogeneous (within the XPS sampling depth) Te4+-depleted layer in Cd-Te mixed oxides. The phenomenon is characterized by an effective sputter yield ratio (STe4+/SCd2+) of 1.83 (±0.06). The anodic oxide on CMT, when cor. for preferential Te4+ sputtering, yields a (Te4+):(Cd2+) ratio of 4.6 (±0.5), in excellent agreement with the bulk Te:Cd ratio in Hg0.8Cd0.2Te. An anodic oxide film compn. of approx. <25 mol % CdTe2O5 and >75 mol % TeO2 and/or mixed Hg-Te oxides is proposed.
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    Leech, P. W.; Gwynn, P. J.; Kibel, M. H. A selective etchant for Hg1–xCdx Te, CdTe and HgTe on GaAs. Appl. Surf. Sci. 1989, 37, 291– 298,  DOI: 10.1016/0169-4332(89)90491-1
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    A selective etchant for mercury cadmium telluride, cadmium telluride, and mercury telluride on gallium arsenide
    Leech, P. W.; Gwynn, P. J.; Kibel, M. H.
    Applied Surface Science (1989), 37 (3), 291-8CODEN: ASUSEE; ISSN:0169-4332.
    A new etchant (KI:I:HBr) for Hg1-xCdxTe, HgTe, and CdTe is developed which is selective in its action with respect to GaAs. The characteristics of the etchant were examd. using MOCVD grown layers on 2° misoriented (100) GaAs substrates with a 0.4 μm CdTe buffer layer. Measurements of the etch rate of the layers give ratios for Hg0.6Cd0.4Te:GaAs of 290:1, for CdTe:GaAs of 273.1 and for HgTe:GaAs of 360:1. In addn., quant. analyses of the layers by XPS were used to compare the surface compositional effects of KI:I:HBr in relation to the Br based etchant, 0.1% (wt./wt.) Br:HBr.
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    Zhang, Z.; Wang, B.; Zhou, P.; Guo, D.; Kang, R.; Zhang, B. A novel approach of chemical mechanical polishing using environment-friendly slurry for mercury cadmium telluride semiconductors. Sci. Rep. 2016, 6, 22466,  DOI: 10.1038/srep22466
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    A novel approach of chemical mechanical polishing using environment-friendly slurry for mercury cadmium telluride semiconductors
    Zhang, Zhenyu; Wang, Bo; Zhou, Ping; Guo, Dongming; Kang, Renke; Zhang, Bi
    Scientific Reports (2016), 6 (), 22466CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    A novel approach of chem. mech. polishing (CMP) is developed for mercury cadmium telluride (HgCdTe or MCT) semiconductors. Firstly, fixed-abrasive lapping is used to machine the MCT wafers, and the lapping soln. is deionized water. Secondly, the MCT wafers are polished using the developed CMP slurry. The CMP slurry consists of mainly SiO2 nanospheres, H2O2, and malic and citric acids, which are different from previous CMP slurries, in which corrosive and toxic chem. reagents are usually employed. Finally, the polished MCT wafers are cleaned and dried by deionized water and compressed air, resp. The novel approach of CMP is environment-friendly. Surface roughness Ra, and peak-to-valley (PV) values of 0.45, and 4.74 nm are achieved, resp. on MCT wafers after CMP. The first and second passivating processes are obsd. in electrochem. measurements on MCT wafers. The fundamental mechanisms of CMP are proposed according to the XPS and electrochem. measurements. Malic and citric acids dominate the first passivating process, and the CMP slurry governs the second process. Te4+3d peaks are absent after CMP induced by the developed CMP slurry, indicating the removing of oxidized films on MCT wafers, which is difficult to achieve using single H2O2 and malic and citric acids solns.
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    Hutson, N. D.; Attwood, B. C.; Scheckel, K. G. XAS and XPS Characterization of Mercury Binding on Brominated Activated Carbon. Environ. Sci. Technol. 2007, 41, 1747– 1752,  DOI: 10.1021/es062121q
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    XAS and XPS Characterization of Mercury Binding on Brominated Activated Carbon
    Hutson, Nick D.; Attwood, Brian C.; Scheckel, Kirk G.
    Environmental Science & Technology (2007), 41 (5), 1747-1752CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
    Brominated powd. activated carbon sorbents have been shown to be quite effective for mercury capture when injected into the flue gas duct at coal-fired power plants and are esp. useful when burning Western US low-chlorine subbituminous coals. X-ray absorption spectroscopy (XAS) and XPS have been used to det. information about the speciation and binding of mercury on two com. available brominated activated carbons. The results are compared with similar anal. of a conventional (nonhalogenated) and chlorinated activated carbon. Both the XAS and XPS results indicate that the mercury, though introduced as elemental vapor, is consistently bound on the carbon in the oxidized form. The conventional and chlorinated activated carbons appeared to contain mercury bound to chlorinated sites and possibly to sulfate species that have been incorporated onto the carbon from adsorbed SO2. The mercury-contg. brominated sorbents appear to contain mercury bound primarily at bromination sites. The mechanism of capture for the sorbents likely consists of surface-enhanced oxidn. of the elemental mercury vapor via interaction with surface-bound halide species with subsequent binding by surface halide or sulfate species.
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    Qiao, S.; Chen, J.; Li, J.; Qu, Z.; Liu, P.; Yan, N.; Jia, J. Adsorption and Catalytic Oxidation of Gaseous Elemental Mercury in Flue Gas over MnOx/Alumina. Ind. Eng. Chem. Res. 2009, 48, 3317– 3322,  DOI: 10.1021/ie801478w
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    Adsorption and Catalytic Oxidation of Gaseous Elemental Mercury in Flue Gas over MnOx/Alumina
    Qiao, Shaohua; Chen, Jie; Li, Jianfeng; Qu, Zan; Liu, Ping; Yan, Naiqiang; Jia, Jinping
    Industrial & Engineering Chemistry Research (2009), 48 (7), 3317-3322CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
    MnOx/Al2O3 catalysts (i.e., impregnating Al2O3 with MnOx) were used to remove elemental Hg from flue gas. MnOx/Al2O3 had significant adsorption performance for Hg capture in the absence of HCl; its favorable adsorption temp. was ∼600° K. However, catalytic oxidn. of Hg became dominant when HCl or Cl2 was present in flue gas; Hg removal efficiency was ≤90% with 20 ppm HCl or 2 ppm Cl2. Also, the catalysts with adsorbed Hg could be chem. regenerated by rinsing with HCl gas to strip off adsorbed Hg as HgCl2. SO2 inhibited Hg adsorption by the catalysts, but this inhibition was less than the catalytic oxidn. of Hg, esp. in the presence of Cl2. XPS and pyrolysis at. absorption spectroscopy anal. results indicated the adsorbed Hg was mainly in the form of mercuric oxide (HgO); the weakly-bonded speciation and their ratio varied with the amt. adsorbed and catalyst Mn content. Multi-functional performance of MnOx/Al2O3 for flue gas Hg removal appeared promising for industrial applications.
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    Araujo, P. T.; Doorn, S. K.; Kilina, S.; Tretiak, S.; Einarsson, E.; Maruyama, S.; Chacham, H.; Pimenta, M. A.; Jorio, A. Third and Fourth Optical Transitions in Semiconducting Carbon Nanotubes. Phys. Rev. Lett. 2007, 98, 067401,  DOI: 10.1103/PhysRevLett.98.067401
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    Third and Fourth Optical Transitions in Semiconducting Carbon Nanotubes
    Araujo, Paulo T.; Doorn, Stephen K.; Kilina, Svetlana; Tretiak, Sergei; Einarsson, Erik; Maruyama, Shigeo; Chacham, Helio; Pimenta, Marcos A.; Jorio, Ado
    Physical Review Letters (2007), 98 (6), 067401/1-067401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    The authors have studied the optical transition energies of single-wall C nanotubes over broad diam. (0.7-2.3 nm) and energy (1.26-2.71 eV) ranges, using their radial breathing mode Raman spectra. The authors establish the diam. and chiral angle dependence of the poorly studied 3rd and 4th optical transitions in semiconducting tubes. Comparative anal. between the higher lying transitions and the 1st and 2nd transitions show 2 different diam. scalings. Quantum mech. calcns. explain the result showing strongly bound excitons in the 1st and 2nd transitions and a delocalized electron wave function in the 3rd transition.
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    Lloyd-Hughes, J.; Jeon, T.-I. A Review of the Terahertz Conductivity of Bulk and Nano-Materials. Journal of Infrared Millimeter and Terahertz Waves 2012, 33, 871,  DOI: 10.1007/s10762-012-9905-y
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    A Review of the Terahertz Conductivity of Bulk and Nano-Materials
    Lloyd-Hughes, James; Jeon, Tae-In
    Journal of Infrared, Millimeter, and Terahertz Waves (2012), 33 (9), 871-925CODEN: JIMTC4; ISSN:1866-6892. (Springer)
    We review pioneering and recent studies of the cond. of solid state systems at terahertz frequencies. A variety of theor. formalisms that describe the terahertz cond. of bulk, mesoscopic and nanoscale materials are outlined, and their validity and limitations are given. Exptl. highlights are discussed from studies of inorg. semiconductors, org. materials (such as graphene, carbon nanotubes and polymers), metallic films and strongly correlated electron systems including superconductors.
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    Burdanova, M. G.; Tsapenko, A. P.; Kharlamova, M. V.; Kauppinen, E. I.; Gorshunov, B. P.; Kono, J.; Lloyd-Hughes, J. A Review of the Terahertz Conductivity and Photoconductivity of Carbon Nanotubes and Heteronanotubes. Advanced Optical Materials 2021, 9, 2101042,  DOI: 10.1002/adom.202101042
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    A Review of the Terahertz Conductivity and Photoconductivity of Carbon Nanotubes and Heteronanotubes
    Burdanova, Maria G.; Tsapenko, Alexey P.; Kharlamova, Marianna V.; Kauppinen, Esko I.; Gorshunov, Boris P.; Kono, Junichiro; Lloyd-Hughes, James
    Advanced Optical Materials (2021), 9 (24), 2101042CODEN: AOMDAX; ISSN:2195-1071. (Wiley-VCH Verlag GmbH & Co. KGaA)
    A review. Terahertz (THz) spectroscopy is an ideal non-contact and non-destructive technique that probes the elec. cond. of nanomaterials. This presents the current status of research in the THz properties of quasi-1D materials, such as nanotubes (NTs) and NT heterostructures. The detailed description of THz exptl. methods (THz time-domain spectroscopy, optical pump-THz probe spectroscopy) and cond. extn. methods are presented along with the phys. models (Drude, plasmon, effective medium theories, etc.) supporting them. Optoelectronic applications, such as optical modulators, switches, and shielding devices, are discussed and illustrate a bright future for these materials.
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    Fagan, J. A.; Hároz, E. H.; Ihly, R.; Gui, H.; Blackburn, J. L.; Simpson, J. R.; Lam, S.; Hight Walker, A. R.; Doorn, S. K.; Zheng, M. Isolation of > 1 nm diameter single-wall carbon nanotube species using aqueous two-phase extraction. ACS Nano 2015, 9, 5377– 5390,  DOI: 10.1021/acsnano.5b01123
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    Isolation of >1 nm Diameter Single-Wall Carbon Nanotube Species Using Aqueous Two-Phase Extraction
    Fagan, Jeffrey A.; Haroz, Erik H.; Ihly, Rachelle; Gui, Hui; Blackburn, Jeffrey L.; Simpson, Jeffrey R.; Lam, Stephanie; Hight Walker, Angela R.; Doorn, Stephen K.; Zheng, Ming
    ACS Nano (2015), 9 (5), 5377-5390CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    In this contribution we demonstrate the effective sepn. of single-wall carbon nanotube (SWCNT) species with diams. larger than 1 nm through multistage aq. two-phase extn. (ATPE), including isolation at the near-monochiral species level up to at least the diam. range of SWCNTs synthesized by elec. arc synthesis (1.3-1.6 nm). We also demonstrate that refined species are readily obtained from both the metallic and semiconducting subpopulations of SWCNTs and that this methodol. is effective for multiple SWCNT raw materials. Using these data, we report an empirical function for the necessary surfactant concns. in the ATPE method for sepg. different SWCNTs into either the lower or upper phase as a function of SWCNT diam. This empirical correlation enables predictive sepn. design and identifies a subset of SWCNTs that behave unusually as compared to other species. These results not only dramatically increase the range of SWCNT diams. to which species selective sepn. can be achieved but also demonstrate that aq. two-phase sepns. can be designed across exptl. accessible ranges of surfactant concns. to controllably sep. SWCNT populations of very small (∼0.62 nm) to very large diams. (>1.7 nm). Together, the results reported here indicate that total sepn. of all SWCNT species is likely feasible by the ATPE method, esp. given future development of multistage automated extn. techniques.
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    Hirano, A.; Tanaka, T.; Urabe, Y.; Kataura, H. PH-and solute-dependent adsorption of single-wall carbon nanotubes onto hydrogels: Mechanistic insights into the metal/semiconductor separation. ACS Nano 2013, 7, 10285– 10295,  DOI: 10.1021/nn4046776
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    pH- and Solute-Dependent Adsorption of Single-Wall Carbon Nanotubes onto Hydrogels: Mechanistic Insights into the Metal/Semiconductor Separation
    Hirano, Atsushi; Tanaka, Takeshi; Urabe, Yasuko; Kataura, Hiromichi
    ACS Nano (2013), 7 (11), 10285-10295CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    The gel sepn. of single-wall carbon nanotubes (SWCNTs) suspended in sodium dodecyl sulfate (SDS) is expected to be one of the most successful methods of large-scale and high-purity sepn. Understanding the mechanism of the gel sepn. helps improve the quality and quantity of sepn. and reveals the colloidal behaviors of SWCNTs, which reflects their band structures. In this study, we characterize the pH- and solute-dependent adsorption of SWCNTs onto agarose and Sephacryl hydrogels and provide a mechanistic model of the metal/semiconductor sepn. The adsorbability of SWCNTs is substantially reduced under acidic pH conditions. Importantly, the pH dependence differs between metallic and semiconducting species; therefore, the adsorbability is related to the band-structure-dependent oxidn. of the SWCNTs. Oxidn. confers pos. charges on SWCNTs, and these charges enhance the electrostatic interactions of the SWCNTs with SDS, thereby leading to the condensation of SDS on the SWCNTs. This increase in SDS d. reduces the interactions between the SWCNTs and hydrogels. Under highly basic conditions, such as pH ∼12.5, or in the presence of salts, the adsorption is dissociative because of the condensation of SDS on the SWCNTs through electrostatic screening by counterions. Desorption of the SWCNTs from the hydrogels due to the addn. of urea implies a hydrophobic interface between SDS-dispersed SWCNTs and the hydrogels. These results suggest that the metal/semiconductor sepn. can be explained by the alteration of the interaction between SDS-dispersed SWCNTs and the hydrogels through changes in the conformation of SDS on the SWCNTs depending on the SWCNTs' band structures.
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    Flavel, B. S.; Moore, K. E.; Pfohl, M.; Kappes, M. M.; Hennrich, F. Separation of single-walled carbon nanotubes with a gel permeation chromatography system. ACS Nano 2014, 8, 1817– 1826,  DOI: 10.1021/nn4062116
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    Separation of Single-Walled Carbon Nanotubes with a Gel Permeation Chromatography System
    Flavel, Benjamin S.; Moore, Katherine E.; Pfohl, Moritz; Kappes, Manfred M.; Hennrich, Frank
    ACS Nano (2014), 8 (2), 1817-1826CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    A gel permeation chromatog. system is used to sep. aq. sodium dodecyl sulfate suspensions of single-walled carbon nanotubes (SWCNTs). This automated procedure requires no precentrifugation, is scalable, and is found to yield monochiral SWCNT fractions of semiconducting SWCNTs with a purity of 61-95%. Unsorted and resulting monochiral fractions are characterized using optical absorption and photoluminescence spectroscopy.
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    Leeuw, T. K.; Tsyboulski, D. A.; Nikolaev, P. N.; Bachilo, S. M.; Arepalli, S.; Weisman, R. B. Strain Measurements on Individual Single-Walled Carbon Nanotubes in a Polymer Host: Structure-Dependent Spectral Shifts and Load Transfer. Nano Lett. 2008, 8, 826– 831,  DOI: 10.1021/nl072861c
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    Strain Measurements on Individual Single-Walled Carbon Nanotubes in a Polymer Host: Structure-Dependent Spectral Shifts and Load Transfer
    Leeuw, Tonya K.; Tsyboulski, Dmitri A.; Nikolaev, Pavel N.; Bachilo, Sergei M.; Arepalli, Sivaram; Weisman, R. Bruce
    Nano Letters (2008), 8 (3), 826-831CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    The fluorescence of individual semiconducting single-walled C nanotubes embedded in polymer films was measured during the application of controlled stretching and compressive strains. Nanotube band gaps shift in systematic patterns that depend on the (n,m) structural type and are in agreement with the predictions of theor. models. Loss of nanotube-host adhesion was revealed by abrupt irregularities in plots of spectral shift vs. strain.
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    Huang, M.; Wu, Y.; Chandra, B.; Yan, H.; Shan, Y.; Heinz, T. F.; Hone, J. Direct measurement of strain-induced changes in the band structure of carbon nanotubes. Phys. Rev. Lett. 2008, 100, 136803,  DOI: 10.1103/PhysRevLett.100.136803
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    Direct Measurement of Strain-Induced Changes in the Band Structure of Carbon Nanotubes
    Huang, Mingyuan; Wu, Yang; Chandra, Bhupesh; Yan, Hugen; Shan, Yuyao; Heinz, Tony F.; Hone, James
    Physical Review Letters (2008), 100 (13), 136803/1-136803/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    The effect of uniaxial strain on the optical transition energies of single-walled C nanotubes with known chiral indexes was measured by Rayleigh scattering spectroscopy. Existing theory accurately predicts the trends in the measured strain-induced shifts, but overestimates their magnitude. Modification of the anal. to account for internal sublattice relaxation results in quant. agreement with expt.
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    Valavala, P. K.; Banyai, D.; Seel, M.; Pati, R. Self-consistent calculations of strain-induced band gap changes in semiconducting (n,0) carbon nanotubes. Physical Review B - Condensed Matter and Materials Physics 2008, 78, 235430,  DOI: 10.1103/PhysRevB.78.235430
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    Self-consistent calculations of strain-induced band gap changes in semiconducting (n,0) carbon nanotubes
    Valavala, Pavan K.; Banyai, Douglas; Seel, Max; Pati, Ranjit
    Physical Review B: Condensed Matter and Materials Physics (2008), 78 (23), 235430/1-235430/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    First-principles d.-functional calcns. of the electronic structure, energy band gaps (Eg), and strain-induced band gap changes in moderate-gap single-walled (n,0) carbon nanotubes (SWNTs) are presented. It is confirmed that (n,0) SWNTs fall into two classes depending upon n mod 3=1 or 2. Eg is always lower for "mod 1" than for "mod 2" SWNTs of similar diam. For n < 10, strong curvature effects dominate Eg; from n = 10 to 17, the Eg oscillations, amplified due to σ-π mixing, decrease and can be explained very well with a tight-binding model which includes trigonal warping. Under strain, the two families of semiconducting SWNTs are distinguished by equal and opposite energy shifts for these gaps. For (10,0) and (20,0) tubes, the potential surface and band gap changes are explored up to approx. ±6% strain or compression. For each strain value, full internal geometry relaxation is allowed. The calcd. band gap changes are ±(115 ± 10) meV per 1% strain, pos. for the mod 1 and neg. for the mod 2 family, about 10% larger than the tight-binding result of ±97 meV and twice as large as the shift predicted from a tight-binding model that includes internal sublattice relaxation.
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    Streit, J.; Snyder, C. R.; Campo, J.; Zheng, M.; Simpson, J. R.; Hight Walker, A. R.; Fagan, J. A. Alkane Encapsulation Induces Strain in Small-Diameter Single-Wall Carbon Nanotubes. J. Phys. Chem. C 2018, 122, 11577– 11585,  DOI: 10.1021/acs.jpcc.8b03166
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    Alkane Encapsulation Induces Strain in Small-Diameter Single-Wall Carbon Nanotubes
    Streit, Jason; Snyder, Chad R.; Campo, Jochen; Zheng, Ming; Simpson, Jeffrey R.; Hight Walker, Angela R.; Fagan, Jeffrey A.
    Journal of Physical Chemistry C (2018), 122 (21), 11577-11585CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    Encapsulation of linear alkane mols. in the endohedral vols. of small-diam. single-wall carbon nanotubes (SWCNTs) is shown to induce diam.-dependent strain on the hexagonal lattice of carbon atoms composing the tubular structure. For the smallest diam. nanotubes, such as the (6,5), (9,1), (8,3), and (10,0), encapsulation leads to expansive radial strain. This effect is demonstrated through precision measurements of induced shifts in the energy of the intrinsic optical transitions of single-chirality nanotube populations. The effect on the optical transitions from strain is found to exceed that of the effective dielec. medium change when comparing the same SWCNT population filled with an alkane vs. those filled with water. This differs from encapsulation of alkanes into larger-diam. nanotubes, for which dielec. effects dominate because of the relative sizes of the guest mols. and the SWCNT cavity. For the SWCNT species examd. in this work, the interior cavity diams. are smaller than the smallest unstrained cross-section of an alkane mol. These results imply that SWCNT species-dependent strain is likely to be encountered when encapsulating any mol. into a SWCNT, with particular complexity to be expected for filling by mols. close to the sieving size of the endohedral cavity.
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    Kashtiban, R. J.; Burdanova, M. G.; Vasylenko, A.; Wynn, J.; Medeiros, P. V.; Ramasse, Q.; Morris, A. J.; Quigley, D.; Lloyd-Hughes, J.; Sloan, J. Linear and Helical Cesium Iodide Atomic Chains in Ultranarrow Single-Walled Carbon Nanotubes: Impact on Optical Properties. ACS Nano 2021, 15, 13389– 13398,  DOI: 10.1021/acsnano.1c03705
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    Linear and Helical Cesium Iodide Atomic Chains in Ultranarrow Single-Walled Carbon Nanotubes: Impact on Optical Properties
    Kashtiban, Reza J.; Burdanova, Maria G.; Vasylenko, Andrij; Wynn, Jamie; Medeiros, Paulo V. C.; Ramasse, Quentin; Morris, Andrew J.; Quigley, David; Lloyd-Hughes, James; Sloan, Jeremy
    ACS Nano (2021), 15 (8), 13389-13398CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
    One-dimensional (1D) at. chains of CsI were previously reported in double-walled carbon nanotubes with ~ 0.8 nm inner diam. Here, we demonstrate that, while 1D CsI chains form within narrow ~ 0.73 nm diam. single-walled carbon nanotubes (SWCNTs), wider SWCNT tubules (~ 0.8-1.1 nm) promote the formation of helical chains of CsI 2 x 1 atoms in cross-section. These CsI helixes create complementary oval distortions in encapsulating SWCNTs with highly strained helixes formed from strained Cs2I2 parallelogram units in narrow tubes to lower strain Cs2I2 units in wider tubes. The obsd. structural changes and charge distribution were analyzed by d.-functional theory and Bader anal. CsI chains also produce conformation-selective changes to the electronic structure and optical properties of the encapsulating tubules. The obsd. defects are an interesting variation from defects commonly obsd. in alkali halides as these are normally assocd. with the Schottky and Frenkel type. The energetics of CsI 2 x 1 helix formation in SWCNTs suggests how these could be controllably formed.
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    Raravikar, N. R.; Keblinski, P.; Rao, A. M.; Dresselhaus, M. S.; Schadler, L. S.; Ajayan, P. M. Temperature dependence of radial breathing mode Raman frequency of single-walled carbon nanotubes. Phys. Rev. B 2002, 66, 235424,  DOI: 10.1103/PhysRevB.66.235424
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    Temperature dependence of radial breathing mode Raman frequency of single-walled carbon nanotubes
    Raravikar, Nachiket R.; Keblinski, Pawel; Rao, Apparao M.; Dresselhaus, Mildred S.; Schadler, Linda S.; Ajayan, Pulickel M.
    Physical Review B: Condensed Matter and Materials Physics (2002), 66 (23), 235424/1-235424/9CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
    Recent high-temp. studies of Raman-active modes in single-walled carbon nanotube (SWNT) bundles report a softening of the radial and tangential band frequencies with increasing sample temp. A few speculations have been proposed in the past to explain the origin of these frequency downshifts. In the present study, based on exptl. data and the results of mol. dynamics simulations, we est. the contributions from 3 factors that may be responsible for the obsd. temp. dependence of the radial breathing mode frequency [ωRBM(T)]. These factors include thermal expansion of individual SWNTs in the radial direction, softening of the C-C (intratubular) bonds, and softening of the van der Waals intertubular interactions in SWNT bundles. Based on our anal., we find that the first factor plays a minor role due to the very small value of the radial thermal expansion coeff. of SWNTs. On the contrary, the temp.-induced softening of the intra- and intertubular bonds contributes significantly to the temp.-dependent shift of ωRBM(T). For nanotubes with diams. (d)≥1.34 nm, the contribution due to the radial thermal expansion is ≤4% over the temp. range used in this study. Interestingly, this contribution increases to ≥10% in the case of nanotubes having d≤0.89 nm due to the relatively larger curvature of these nanotubes. The contributions from the softening of the intra- and intertubular bonds are approx. equal. These 2 factors together contribute a total of about ∼95% and 90%, resp., for SWNTs having d≥1.34 nm and ≤0.89 nm.
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    May, P.; Telg, H.; Zhong, G.; Robertson, J.; Thomsen, C.; Maultzsch, J. Observation of excitonic effects in metallic single-walled carbon nanotubes. Phys. Rev. B 2010, 82, 195412,  DOI: 10.1103/PhysRevB.82.195412
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    Observation of excitonic effects in metallic single-walled carbon nanotubes
    May, Patrick; Telg, Hagen; Zhong, Guofang; Robertson, John; Thomsen, Christian; Maultzsch, Janina
    Physical Review B: Condensed Matter and Materials Physics (2010), 82 (19), 195412/1-195412/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    Excitonic effects of metallic single-walled carbon nanotubes are measured with temp.-dependent resonant Raman spectroscopy. By changing the temp. in the range of 300-870 K, we observe variations in the optical transition energy Eii as well as in the max. Raman intensity. We find both dependences to be different for semiconducting and metallic single-walled carbon nanotubes. We suggest an interpretation in terms of excitons dissocd. into free electron-hole pairs at temps. related to the exciton binding energy. We furthermore discuss how the oscillator strength is influenced by temp.
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    The authors report a study of 2nd-order combination and overtone modes in highly ordered pyrolytic graphite (HOPG), in single-wall C nanotube (SWNT) bundles and in isolated SWNTs. The authors found both dispersive and nondispersive Raman bands in the range 1650-2100 cm-1, and the appearance and frequency vs. laser energy Elaser behavior of these features are in agreement with predictions from double-resonance Raman theory. In the case of SWNTs, these 2nd-order bands depend on the 1-dimensional structure of SWNTs, and at the single nanotube level, the spectra vary from tube to tube, depending on tube diam. and chirality and on the energy of the van Hove singularity relative to Elaser.
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    Carbon (2011), 49 (4), 1318-1325CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Single-walled carbon nanotubes (SWCNTs) with varying degrees of disorder were investigated using multiple-excitation Raman spectroscopy. The lattice disorder was imparted into the nanotubes by the addn. of varying amts. of sulfur to the iron catalyst in a thermal chem. vapor deposition process. Changes in the intensities of peaks occurring due to a double resonance Raman process were studied. The intensity of the disorder-induced D band increased with a decrease in the sulfur content. Upon post-synthesis heat treatment, the double resonance process got quenched due to defect healing. The second order G' band and iTOLA bands exhibited a two-peak structure, of which one of the peaks is relatively more sensitive to defects and decreased in intensity with heat treatment.
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    We have investigated reversible single-wall carbon nanotube (SWNT) oxidn. by quant. anal. of the oxide-induced absorption bleaching and luminescence quenching at low pH. These data, in combination with DFT structure calcns., suggest that the nanotube oxide is a 1,4-endoperoxide. At low pH, the endoperoxide protonates to create a hydroperoxide carbocation, introducing a hole in the SWNT valence band. Nanotube luminescence is extremely sensitive to quenching by hole-doping, while the absorption is relatively robust.
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    The time scales for interfacial charge sepn. and recombination play crucial roles in detg. efficiencies of excitonic photovoltaics. Near-IR photons are harvested efficiently by semiconducting single-walled carbon nanotubes (SWCNTs) paired with appropriate electron acceptors, such as fullerenes (e.g., C60). However, little is known about crucial photochem. events that occur on femtosecond to nanosecond time scales at such heterojunctions. Here, we present transient absorbance measurements that utilize a distinct spectroscopic signature of charges within SWCNTs, the absorbance of a trion quasiparticle, to measure both the ultrafast photoinduced electron transfer time (τpet) and yield (.vphi.pet) in photoexcited SWCNT-C60 bilayer films. The rise time of the trion-induced absorbance enables the detn. of the photoinduced electron transfer (PET) time of τpet ≤ 120 fs, while an exptl. detd. trion absorbance cross section reveals the yield of charge transfer (.vphi.pet ≈ 38 ± 3%). The extremely fast electron transfer times obsd. here are on par with some of the best donor:acceptor pairs in excitonic photovoltaics and underscore the potential for efficient energy harvesting in SWCNT-based devices.
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    Nanoscale (2015), 7 (4), 1383-1391CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
    Controlled doping of carbon nanotubes is elemental for their electronic applications. Here we report an approach to tune the polarity and degree of doping of single-walled carbon nanotubes via filling with nickelocene followed by encapsulated reactions. Using Raman, photoemission spectroscopy and transmission electron microscopy, we show that nickelocene mols. transform into nickel carbides, nickel and inner carbon nanotubes with reaction temps. as low as 250 °C. The doping efficiency is detd. for each chem. component. Synchronous charge transfer among the mol. components allows bipolar doping of the carbon nanotubes to be achieved in a broad range of ±0.0012 e- per carbon.
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    Journal of Physical Chemistry C (2008), 112 (12), 4507-4516CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
    The authors used femtosecond transient absorption (TA) spectroscopy to examine the excited state dynamics of single-walled C nanotube (SWNT) bundles embedded in polymer matrixes. The SWNTs were excited by a femtosecond pump pulse centered at either 1800, 900, or 550 nm and probed using a white-light continuum extending from 400 to 750 nm. The authors obsd. a structured TA spectrum consisting of narrow induced transmission (IT) and induced absorption (IA) bands. The TA spectrum, which is independent of excitation wavelength, appeared on a time scale shorter than instrument response (200 fs) and persisted for up to 100 ps. TA spectra obtained at pump-probe delay times provided a window through which to monitor the exciton dynamics. The authors obsd. 3 distinct spectral signatures in the time-dependent data: (1) the decay of a broad photobleach, (2) the biphasic decay of narrow IT and IA features, and (3) a dynamical spectral shift of IA bands. These processes were attributed to plasmon relaxation, electron-hole recombination, and lattice relaxation assocd. with exciton self-trapping, resp. Anal. of the transient spectrum suggested that it arose from a nonlinear optical response of the SWNT, where excitons produced by the pump pulse modified the transition frequencies of subsequent carrier excitations. The result was IT bands (bleaches) at the ground state absorption frequencies, and assocd. with each were a corresponding red-shifted absorption band. These induced absorptions were attributed to the formation of biexcitons, 4-particle excitations that are produced through the sequential excitation of 2 closely spaced electron-hole pairs.
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    Physical Review B: Condensed Matter and Materials Physics (2013), 87 (20), 205412/1-205412/7CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    We present a study of free carrier photogeneration and multicarrier bound states, such as biexcitons and trions (charged excitons), in semiconducting single-walled carbon nanotubes. Pump-and-probe measurements performed with fs pulses reveal the effects of strong Coulomb interactions between carriers on their dynamics. Biexciton formation by optical transition from exciton population results in an induced absorption line (binding energy 130 meV). Exciton-exciton annihilation process is shown to evolve at high densities towards an Auger process that can expel carriers from nanotubes. The remaining carriers give rise to an induced absorption due to trion formation (binding energy 190 meV). These features show the dynamics of exciton and free carriers populations.
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    Chemical Physics Letters (2007), 442 (4-6), 394-399CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
    The authors theor. study the environmental effect for optical transition energies of single-walled C nanotubes (SWNTs), by calcg. the exciton transition energies of SWNTs. The static dielec. consts. used in the exciton calcn. can be expressed as a function of the dielec. consts. of the surrounding material and that of the SWNT, in which the static and dynamic dielec. consts. of the SWNT represent the screening effect of core electrons and the valence π electrons, resp. The calcd. results reproduce the environmental effect of the exptl. transition energies for various surrounding materials and for various diams. of SWNTs.
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    Physical Review Letters (2013), 111 (19), 197401/1-197401/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Exciton-exciton recombination in isolated semiconducting single-walled carbon nanotubes was studied using femtosecond transient absorption. Under sufficient excitation to sat. the optical absorption, we obsd. an abrupt transition between reaction- and diffusion-limited kinetics, arising from reactions between incoherent localized excitons with a finite probability of ∼0.2 per encounter. This represents the first exptl. observation of a crossover between classical and crit. kinetics in a 1D coalescing random walk, which is a paradigm for the study of nonequil. systems.
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    Graphene nanoribbons display extraordinary optical properties due to one-dimensional quantum-confinement, such as width-dependent bandgap and strong electron-hole interactions, responsible for the formation of excitons with extremely high binding energies. Here we use femtosecond transient absorption spectroscopy to explore the ultrafast optical properties of ultranarrow, structurally well-defined graphene nanoribbons as a function of the excitation fluence, and the impact of enhanced Coulomb interaction on their excited states dynamics. We show that in the high-excitation regime biexcitons are formed by nonlinear exciton-exciton annihilation, and that they radiatively recombine via stimulated emission. We obtain a biexciton binding energy of ≈250 meV, in very good agreement with theor. results from quantum Monte Carlo simulations. These observations pave the way for the application of graphene nanoribbons in photonics and optoelectronics.
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    Shao, D.; Yotprayoonsak, P.; Saunajoki, V.; Ahlskog, M.; Virtanen, J.; Kangas, V.; Volodin, A.; Haesendonck, C.; Burdanova, M.; Mosley, C.; Lloyd-Hughes, J. Conduction properties of thin films from a water soluble carbon nanotube/hemicellulose complex. Nanotechnology 2018, 29, 145203,  DOI: 10.1088/1361-6528/aaabd1
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    Nanotechnology (2018), 29 (14), 145203/1-145203/9CODEN: NNOTER; ISSN:1361-6528. (IOP Publishing Ltd.)
    We have examd. the conductive properties of carbon nanotube based thin films, which were prepd. via dispersion in water by non-covalent functionalization of the nanotubes with xylan, a type of hemicellulose. Measurements of low temp. cond., Kelvin probe force microscopy, and high frequency (THz) cond. elucidated the intra-tube and inter-tube charge transport processes in this material. The measurements show excellent conductive properties of the as prepd. thin films, with bulk cond. up to 2000 S cm-1. The transport results demonstrate that the hemicellulose does not seriously interfere with the inter-tube conductance.
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    Schneck, J. R.; Walsh, A. G.; Green, A. A.; Hersam, M. C.; Ziegler, L. D.; Swan, A. K. Electron correlation effects on the femtosecond dephasing dynamics of e 22 excitons in (6,5) carbon nanotubes. J. Phys. Chem. A 2011, 115, 3917– 3923,  DOI: 10.1021/jp108345t
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    Electron Correlation Effects on the Femtosecond Dephasing Dynamics of E22 Excitons in (6,5) Carbon Nanotubes
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    Journal of Physical Chemistry A (2011), 115 (16), 3917-3923CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
    Highly nonlinear pump fluence dependence was obsd. in the ultrafast 1-color pump-probe responses excited by 38 fs pulses resonant with the E22 transition in a room-temp. soln. of (6,5) C nanotubes. The differential probe transmission (ΔT/T) at the peak of the pump-probe response (τ = 20 fs) was measured for pump fluences from ∼1013 to 1017 photons/pulse cm2. The onset of satn. is obsd. at ∼2 × 1015 photons/pulse cm2 (∼8 × 105 excitons/cm). At pump fluences >4 × 1016 photons/pulse cm2 (∼1.6 × 106 excitons/cm), ΔT/T decreases as the pump fluence increases. Analogous signal satn. behavior was obsd. for all measured probe delays. Despite the high exciton d. at satn., no change in the E22 population decay rate was obsd. at short times (<300 fs). The pump probe signal was modeled by a 3rd-order perturbation theory treatment that includes the effects of inhomogeneous broadening. The obsd. ΔT/T signal is well-fit by a pump-fluence-dependent dephasing rate linearly dependent on the no. of excitons created by the pump pulse. Therefore, the obsd. nonlinear pump intensity dependence is attributed to the effects of quasi-elastic exciton-exciton interactions on the dephasing rates of single C nanotubes. The low fluence total dephasing time is 36 fs, corresponding to a homogeneous width of 36 meV (290 cm-1), and the derived E22 inhomogeneous width is 68 meV (545 cm-1). These results are contrasted with photon-echo-derived parameters for the E11 transition.
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  1. Zhou Fang, Xin Feng, Xinxia Li, Xinyuan Tang, Ya Xu, Yan He, Huifang Li. Theoretical Studies for Improving the Dispersion of Carbon Nanotubes in Caprolactam Polymers by Enhancing the Intermolecular Interactions with Functionalization: Implications for Reinforced Polymer Composites. ACS Applied Nano Materials 2024, 7 (19) , 22581-22591. https://doi.org/10.1021/acsanm.4c03066
  2. Griffin M. Milligan, Ze-Fan Yao, Dmitri Leo Mesoza Cordova, Baixin Tong, Maxx Q. Arguilla. Single Quasi-1D Chains of Sb2Se3 Encapsulated within Carbon Nanotubes. Chemistry of Materials 2024, 36 (2) , 730-741. https://doi.org/10.1021/acs.chemmater.3c02114
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  • Abstract

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    Figure 1

    Figure 1. (a) Schematic diagram to depict the methods of preparing SWCNT samples in different existing states. (b) Left: ADF-STEM images of the HgTe NW-filled semiconducting SWCNTs. Green and violet arrows mark the one-atom-thick zigzag NWs and wider NWs observed from the ADF-STEM image. Middle: Experimental (top) and simulated (bottom) bright-field high-resolution TEM images of two SWCNTs filled by zigzag atomic NWs. Right: Structure model of zigzag atomic NW-filled (7,6) SWCNTs. (c) UV–vis–NIR absorption spectra of SWCNT samples in different states. The dashed curve is the rescaled absorption spectrum of a blank gelatin film. The inset shows the absorption spectra of the vacuum-filtered thin films at higher energies, which revealed the π-plasma feature.

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    Figure 2

    Figure 2. (a) XPS Hg 4f (top) and Te 3d (bottom) spectra of the vacuum-filtered HgTe-filled semiconducting SWCNT thin films. (b) THz conductivity of vacuum-filtered SWCNT films (points) and simulated values based on the surface plasmon model (lines). The dotted, dashed, and dot-dashed curves, shown offset at the bottom of figure, are the three plasma oscillators contributing to the simulated conductivity spectrum of a HgTe-filled SWCNT film (blue solid curve). The plasma resonance frequency for each oscillator is denoted in the figure. (c) PLE contour map of the HgTe-filled gelatin-embedded SWCNT film. Black and white dots represent the interband energy values obtained based on the empirical model in ref (44) and the experimental energy values of these SWCNTs in solution. The orange diamond marks an assigned phonon sideband feature of (7,5). (d) Excitonic energy shifts of various (n,m) species as a result of changes in the surrounding medium, ΔEii. (e) Excitonic energy shifts induced by changes in the temperature, ΔEii = Eii,298 K – Eii,80 K.

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    Figure 3

    Figure 3. Temperature-dependent Raman spectra of the vacuum-filtered unfilled (a and b) and HgTe-filled (c and d) thin films in the RBM regime under an excitation wavelength of 660 nm (a and c) and 532 nm (b and d). The dashed vertical lines in panels c and d mark the central frequencies of the room-temperature RBM peaks for the corresponding unfilled SWCNT samples. Changes in the Raman shifts of different Raman modes for the unfilled (open circles) and HgTe-filled (solid circles) SWCNT film samples against temperature under 660 nm (e) and 532 nm (f) excitation. The dotted and solid straight lines are linear fits to the data points. The extracted thermal constants (dωmode/dT) and their errors based on a linear fit to the data are presented in the graphs.

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    Figure 4

    Figure 4. (a–f) Heatmaps of the differential transmission signals [ΔOD(t)/ΔOD0] of the solution-state SWCNTs against probe energies (1.15–1.35 eV) and pump–probe delays at various pump energies. (g–i) Corresponding spectra averaged over a time window from 0.4 to 1.5 ps. The dashed curves were added in parts a–f to indicate the spectral profiles of the GSB features. The vertical lines and arrows in parts g and i indicate the spectral shifts of GSB for (7,5) and (6,5), respectively.

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    Figure 5

    Figure 5. (a) Schematic showing that the suppression of in-plane (stretching and bending) and out-of-plane (radial breathing) vibrational movements due to SWCNT filling results in an increased stiffness of the nanotube upon photoexcitation. The proposed mechanism is based on the assumption that lattice vibrations along both the in-plane and out-of-plane directions are unrestricted in the liquid environment. (b) TA spectra of SWCNTs in different states averaged over a time window from 0.4 to 0.9 ps with different pump energies. All spectra were normalized to the minimum values of the corresponding GSB feature located at around 1.2 eV. Representative semilog and log–log TA kinetic curves of gelatin-embedded SWCNT films at a pump energy of (c and d) 3.542 eV and (e and f) 2.44 eV. The straight lines in panels d and f are the power-law fits [n(t) ∝tα] to the experimental data.

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  • References

    This article references 68 other publications.

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      Giant Raman scattering from J-aggregated dyes inside carbon nanotubes for multispectral imaging
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      Raman spectroscopy uses visible light to acquire vibrational fingerprints of mols., thus making it a powerful tool for chem. anal. in a wide range of media. However, its potential for optical imaging at high resoln. is severely limited by the fact that the Raman effect is weak. Here, we report the discovery of a giant Raman scattering effect from encapsulated and aggregated dye mols. inside single-walled carbon nanotubes. Measurements performed on rod-like dyes such as α-sexithiophene and β-carotene, assembled inside single-walled carbon nanotubes as highly polarizable J-aggregates, indicate a resonant Raman cross-section of (3 ± 2) × 10-21 cm2 sr-1, which is well above the cross-section required for detecting individual aggregates at the highest optical resoln. Free from fluorescence background and photobleaching, this giant Raman effect allows the realization of a library of functionalized nanoprobe labels for Raman imaging with robust detection using multispectral anal.
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      Asymmetric dyes align inside carbon nanotubes to yield a large nonlinear optical response
      Cambre, Sofie; Campo, Jochen; Beirnaert, Charlie; Verlackt, Christof; Cool, Pegie; Wenseleers, Wim
      Nature Nanotechnology (2015), 10 (3), 248-252CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
      Asym. dye mols. have unusual optical and electronic properties. For instance, they show a strong 2nd-order nonlinear optical (NLO) response that has attracted great interest for potential applications in electrooptic modulators for optical telecommunications and in wavelength conversion of lasers. However, the strong Coulombic interaction between the large dipole moments of these mols. favors a pairwise antiparallel alignment that cancels out the NLO response when incorporated into bulk materials. Here, by including an elongated dipolar dye (p,p'-dimethylaminonitrostilbene, DANS, a prototypical asym. dye with a strong NLO response) inside single-walled C nanotubes (SWCNTs), an ideal head-to-tail alignment in which all elec. dipoles point in the same sense is naturally created. The authors have applied this concept to synthesize soln.-processible DANS-filled SWCNTs that show an extremely large total dipole moment and static hyperpolarizability (β0 = 9,800 × 10-30 e.s.u.), resulting from the coherent alignment of arrays of ∼70 DANS mols.
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      Observation of extreme phase transition temperatures of water confined inside isolated carbon nanotubes
      Agrawal, Kumar Varoon; Shimizu, Steven; Drahushuk, Lee W.; Kilcoyne, Daniel; Strano, Michael S.
      Nature Nanotechnology (2017), 12 (3), 267-273CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
      Fluid phase transitions inside single, isolated carbon nanotubes are predicted to deviate substantially from classical thermodn. This behavior enables the study of ice nanotubes and the exploration of their potential applications. The authors report measurements of the phase boundaries of water confined within six isolated carbon nanotubes of different diams. (1.05, 1.06, 1.15, 1.24, 1.44 and 1.52 nm) using Raman spectroscopy. The results reveal an exquisite sensitivity to diam. and substantially larger temp. elevations of the freezing transition (by as much as 100 °C) than have been theor. predicted. Dynamic water filling and reversible freezing transitions were marked by 2-5 cm-1 shifts in the radial breathing mode frequency, revealing reversible melting bracketed to 105-151 °C and 87-117 °C for 1.05 and 1.06 nm single-walled carbon nanotubes, resp. Near-ambient phase changes were obsd. for 1.44 and 1.52 nm nanotubes, bracketed between 15-49 °C and 3-30 °C, resp., whereas the depression of the f.p. was obsd. for the 1.15 nm nanotube between -35 and 10 °C. The interior aq. phase reversibly decreases the axial thermal cond. of the nanotube by as much as 500%, allowing digital control of the heat flux.
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      Serpell, C. J.; Rutte, R. N.; Geraki, K.; Pach, E.; Martincic, M.; Kierkowicz, M.; De Munari, S.; Wals, K.; Raj, R.; Ballesteros, B.; Tobias, G.; Anthony, D. C.; Davis, B. G. Carbon nanotubes allow capture of krypton, barium and lead for multichannel biological X-ray fluorescence imaging. Nat. Commun. 2016, 7, 1– 10,  DOI: 10.1038/ncomms13118
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      Nakanishi, R.; Kitaura, R.; Warner, J. H.; Yamamoto, Y.; Arai, S.; Miyata, Y.; Shinohara, H. Thin single-wall BN-nanotubes formed inside carbon nanotubes. Sci. Rep. 2013, 3, 1– 6,  DOI: 10.1038/srep01385
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      Cabana, L.; Ballesteros, B.; Batista, E.; Magén, C.; Arenal, R.; Orõ-Solé, J.; Rurali, R.; Tobias, G. Synthesis of PbI2 Single-Layered Inorganic Nanotubes Encapsulated Within Carbon Nanotubes. Adv. Mater. 2014, 26, 2016– 2021,  DOI: 10.1002/adma.201305169
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      Synthesis of PbI2 Single-Layered Inorganic Nanotubes Encapsulated Within Carbon Nanotubes
      Cabana, Laura; Ballesteros, Belen; Batista, Eudar; Magen, Cesar; Arenal, Raul; Oro-Sole, Judith; Rurali, Riccardo; Tobias, Gerard
      Advanced Materials (Weinheim, Germany) (2014), 26 (13), 2016-2021CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A solvent-free high temp. route was explored that allows the formation of high quality, single-cryst. inorg. nanotubes. The authors have produced an interesting hybrid cor-shell structure combining 2 different tubular materials: single-layered PbI2 nanotubes@carbon nanotubes (CNTs). Above the threshold of 3.5 nm, the single-layered PbI2 can be easily molded to the inner diam. of the hosting CNT template. The diam. of the inorg. nanotubes prepd. herein is merely dependent on the diam. of the host. Therefore inorg. nanotubes of a given diam. can be prepd. by simply using a sample of CNTs with uniform inner diam. These coupled 1D nanostructures will offer very promising technol. applications where materials having well defined electronic optic or optoelectronic properties are required.
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      Ashokkumar, A. E.; Enyashin, A. N.; Deepak, F. L. Single Walled BiI3 Nanotubes Encapsulated within Carbon Nanotubes. Sci. Rep. 2018, 8, 1– 8,  DOI: 10.1038/s41598-018-28446-2
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      Single Walled BiI3 Nanotubes Encapsulated within Carbon Nanotubes
      Ashokkumar, Anumol Erumpukuthickal; Enyashin, Andrey N.; Deepak, Francis Leonard
      Scientific Reports (2018), 8 (1), 1-8CODEN: SRCEC3; ISSN:2045-2322. (Nature Research)
      Inorg. nanotubes are morphol. counterparts of carbon nanotubes (CNTs). Yet, only graphene-like BN layer has been readily organized into single walled nanotubes so far. In this study, we present a simple route to obtain inorg. single walled nanotubes - a novel ultrathin morphol. for bismuth iodide (BiI3), embedded within CNTs. The synthesis involves the capillary filling of BiI3 into CNT, which acts as a nanotemplate, by annealing the BiI3-CNT mixt. above the m.p. of BiI3. Aberration cor. scanning/transmission electron microscopy is used in characterizing the novel morphol. of BiI3. A crit. diam. which enables the formation of BiI3 nanotubes, against BiI3 nanorods is identified. The relative stability of these phases is investigated with the d. functional theory calcns. Remarkably, the calcns. reveal that the single walled BiI3 nanotubes are semiconductors with a direct band gap, which remain stable even without the host CNTs.
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    10. 10
      Nakanishi, Y.; Omachi, H.; Fokina, N. A.; Schreiner, P. R.; Kitaura, R.; Dahl, J. E.; Carlson, R. M.; Shinohara, H. Template Synthesis of Linear-Chain Nanodiamonds Inside Carbon Nanotubes from Bridgehead-Halogenated Diamantane Precursors. Angew. Chem., Int. Ed. 2015, 54, 10802– 10806,  DOI: 10.1002/anie.201504904
      10
      Template Synthesis of Linear-Chain Nanodiamonds Inside Carbon Nanotubes from Bridgehead-Halogenated Diamantane Precursors
      Nakanishi, Yusuke; Omachi, Haruka; Fokina, Natalie A.; Schreiner, Peter R.; Kitaura, Ryo; Dahl, Jeremy E. P.; Carlson, Robert M. K.; Shinohara, Hisanori
      Angewandte Chemie, International Edition (2015), 54 (37), 10802-10806CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A simple method for the synthesis of linear-chain diamond-like nanomaterials, so-called diamantane polymers, is described. This synthetic approach is primarily based on a template reaction of dihalogen-substituted diamantane precursors in the hollow cavities of carbon nanotubes. Under high vacuum and in the presence of Fe nanocatalyst particles, the dehalogenated radical intermediates spontaneously form linear polymer chains within the carbon nanotubes. Transmission electron microscopy reveals the formation of well-aligned linear polymers. We expect that the present template-based approach will enable the synthesis of a diverse range of linear-chain polymers by choosing various precursor mols. The present technique may offer a new strategy for the design and synthesis of one-dimensional nanomaterials.
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    11. 11
      Hart, M.; White, E. R.; Chen, J.; McGilvery, C. M.; Pickard, C. J.; Michaelides, A.; Sella, A.; Shaffer, M. S.; Salzmann, C. G. Encapsulation and Polymerization of White Phosphorus Inside Single-Wall Carbon Nanotubes. Angew. Chem., Int. Ed. 2017, 56, 8144– 8148,  DOI: 10.1002/anie.201703585
      11
      Encapsulation and Polymerization of White Phosphorus Inside Single-Wall Carbon Nanotubes
      Hart, Martin; White, Edward R.; Chen, Ji; McGilvery, Catriona M.; Pickard, Chris J.; Michaelides, Angelos; Sella, Andrea; Shaffer, Milo S. P.; Salzmann, Christoph G.
      Angewandte Chemie, International Edition (2017), 56 (28), 8144-8148CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Elemental phosphorus displays an impressive no. of allotropes with highly diverse chem. and phys. properties. White phosphorus has now been filled into single-wall carbon nanotubes (SWCNTs) from the liq. and thereby stabilized against the highly exothermic reaction with atm. oxygen. The encapsulated tetraphosphorus mols. were visualized with transmission electron microscopy, but found to convert readily into chain structures inside the SWCNT "nanoreactors". The energies of the possible chain structures were detd. computationally, highlighting a delicate balance between the extent of polymn. and the SWCNT diam. Exptl., a single-stranded zig-zag chain of phosphorus atoms was obsd., which is the lowest energy structure at small confinement diams. These one-dimensional chains provide a glimpse into the very first steps of the transformation from white to red phosphorus.
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    12. 12
      Qin, J. K.; Liao, P. Y.; Si, M.; Gao, S.; Qiu, G.; Jian, J.; Wang, Q.; Zhang, S. Q.; Khin Yap, Y.; Ye, P. D.; Huang, S.; Charnas, A.; Wang, Y.; Kim, M. J.; Wu, W.; Xu, X.; Wang, H. Y.; Yang, L. Raman response and transport properties of tellurium atomic chains encapsulated in nanotubes. Nature Electronics 2020, 3, 141– 147,  DOI: 10.1038/s41928-020-0365-4
      12
      Raman response and transport properties of tellurium atomic chains encapsulated in nanotubes
      Qin, Jing-Kai; Liao, Pai-Ying; Si, Mengwei; Gao, Shiyuan; Qiu, Gang; Jian, Jie; Wang, Qingxiao; Zhang, Si-Qi; Huang, Shouyuan; Charnas, Adam; Wang, Yixiu; Kim, Moon J.; Wu, Wenzhuo; Xu, Xianfan; Wang, Hai-Yan; Yang, Li; Khin Yap, Yoke; Ye, Peide D.
      Nature Electronics (2020), 3 (3), 141-147CODEN: NEALB3; ISSN:2520-1131. (Nature Research)
      Tellurium can form nanowires of helical at. chains. With their unique one-dimensional van der Waals structure, these nanowires are expected to show phys. and electronic properties that are remarkably different from those of bulk tellurium. Here, we show that few-chain and single-chain van der Waals tellurium nanowires can be isolated using carbon nanotube and boron nitride nanotube encapsulation. With this approach, the no. of at. chains can be controlled by the inner diam. of the nanotube. The Raman response of the structures suggests that the interaction between a single-at. tellurium chain and a carbon nanotube is weak, and that the inter-chain interaction becomes stronger as the no. of chains increases. Compared with bare tellurium nanowires on SiO2, nanowires encapsulated in boron nitride nanotubes exhibit a dramatically enhanced current-carrying capacity, with a c.d. of 1.5 × 108 A cm-2 that exceeds that of most semiconducting nanowires. We also use our tellurium nanowires encapsulated in boron nitride nanotubes to create field-effect transistors with a diam. of only 2 nm.
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      Hu, Z.; Breeze, B.; Kashtiban, R. J.; Sloan, J.; Lloyd-Hughes, J. Zigzag HgTe Nanowires Modify the Electron-Phonon Interaction in Chirality-Refined Single-Walled Carbon Nanotubes. ACS Nano 2022, 16, 6789– 6800,  DOI: 10.1021/acsnano.2c01647
      13
      Zigzag HgTe Nanowires Modify the Electron-Phonon Interaction in Chirality-Refined Single-Walled Carbon Nanotubes
      Hu, Ziyi; Breeze, Ben; Kashtiban, Reza J.; Sloan, Jeremy; Lloyd-Hughes, James
      ACS Nano (2022), 16 (4), 6789-6800CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Atomically thin nanowires (NWs) can be synthesized inside single-walled carbon nanotubes (SWCNTs) and feature unique crystal structures. Here we show that HgTe nanowires formed inside small-diam. (<1 nm) SWCNTs can advantageously alter the optical and electronic properties of the SWCNTs. Metallic purifn. of the filled SWCNTs was achieved by a gel column chromatog. method, leading to an efficient extn. of the semiconducting and metallic portions with known chiralities. Electron microscopic imaging revealed that zigzag HgTe chains were the dominant NW geometry in both the semiconducting and metallic species. Equil.-state and ultrafast spectroscopy demonstrated that the coupled electron-phonon system was modified by the encapsulated HgTe NWs, in a way that varied with the chirality. For semiconducting SWCNTs with HgTe NWs, Auger relaxation processes were suppressed, leading to enhanced photoluminescence emission. In contrast, HgTe NWs enhanced the Auger relaxation rate of metallic SWCNTs and created faster phonon relaxation, providing exptl. evidence that encapsulated at. chains can suppress hot carrier effects and therefore boost electronic transport.
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      Woan, K.; Pyrgiotakis, G.; Sigmund, W. Photocatalytic Carbon-Nanotube-TiO2 Composites. Adv. Mater. 2009, 21, 2233– 2239,  DOI: 10.1002/adma.200802738
      14
      Photocatalytic Carbon-Nanotube-TiO2 Composites
      Woan, Karran; Pyrgiotakis, Georgios; Sigmund, Wolfgang
      Advanced Materials (Weinheim, Germany) (2009), 21 (21), 2233-2239CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. The literature and advances in photocatalysis based on the combination of titania (TiO2) and carbon nanotubes is presented. The semiconductor basis for photocatalysis is introduced for anatase and rutile. Furthermore, the proposed mechanisms of catalytic enhancement resulting from the pairing of the titania semiconductor with either metallic, semiconducting, or defect-rich carbon nanotubes (CNT) is discussed. Differences are apparent for the mixts. and chem. bonded CNT-TiO2 composites. The article then highlights the recent advances in the synthesis techniques for these composites and their photocatalytic reactions with org., inorg., and biol. agents. Finally, various applications and challenges for these composite materials are reported.
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    15. 15
      González-Muñoz, D.; Martín-Somer, A.; Strobl, K.; Cabrera, S.; De Pablo, P. J.; Díaz-Tendero, S.; Blanco, M.; Alemán, J. Enhancing Visible-Light Photocatalysis via Endohedral Functionalization of Single-Walled Carbon Nanotubes with Organic Dyes. ACS Appl. Mater. Interfaces 2021, 13, 24877– 24886,  DOI: 10.1021/acsami.1c04679
      15
      Enhancing Visible-Light Photocatalysis via Endohedral Functionalization of Single-Walled Carbon Nanotubes with Organic Dyes
      Gonzalez-Munoz, Daniel; Martin-Somer, Ana; Strobl, Klara; Cabrera, Silvia; De Pablo, Pedro J.; Diaz-Tendero, Sergio; Blanco, Matias; Aleman, Jose
      ACS Applied Materials & Interfaces (2021), 13 (21), 24877-24886CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)
      The encapsulation of an org. dye, 10-phenylphenothiazine (PTH), in the inner cavity of single-walled carbon nanotubes (SWNTs) as a breaking heterogenization strategy is presented. The PTH@oSWNT material was microscopically and spectroscopically characterized, showing intense photoemission when illuminated with visible light at the nanoscale. Thus, PTH@oSWNT was employed as a heterogeneous photocatalyst in single electron transfer dehalogenation reactions under visible light irradn. The material showed an enhanced photocatalytic activity, achieving turnover nos. as high as 3200, with complete recyclability and stability for more than eight cycles. Computational calcns. confirm that electronic communication between both partners is established because, upon illumination, an electron of the excited PTH is transferred from the π system of the mol. to the delocalized π-cloud of the SWNT, thus justifying the enhanced photocatalytic activity.
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      Zhang, J.; Dai, M.; Zhang, S.; Dai, M.; Zhang, P.; Wang, S.; He, Z. Recent Progress on Carbon-Nanotube-Based Materials for Photocatalytic Applications: A Review. Solar RRL 2022, 6, 2200243,  DOI: 10.1002/solr.202200243
      16
      Recent Progress on Carbon-Nanotube-Based Materials for Photocatalytic Applications: A Review
      Zhang, Jing; Dai, Mingchong; Zhang, Shijie; Dai, Meng; Zhang, Peng; Wang, Shuguang; He, Zuoli
      Solar RRL (2022), 6 (9), 2200243CODEN: SRORAW; ISSN:2367-198X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. As one of the most outstanding allotropes of carbon assembled with a cylindrical nanostructure, carbon nanotubes (CNTs) have attracted extensive attention in the areas of material science and engineering due to their unique structural characteristics and physicochem. properties. Very recently, versatile hierarchical CNT-based photocatalysts are of considerable interest in current research and applications ranging from fuel generation to environmental purifn. Therefore, it is necessary to summarize the CNT-based photocatalysts to provide essential refs. for the continuous research study. In this review, the different design strategies and flexible functionalizations for prototype construction are described and their typical research, esp. the structure-related or electronic-effected mechanism in the photocatalytic reaction of pollutants degrdation, water splitting, and CO2 redn. overviewed. Finally, the various aspects of CNT-based photocatalysts are discussed for future developments in compd. applications.
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      Spencer, J. H.; Nesbitt, J. M.; Trewhitt, H.; Kashtiban, R. J.; Bell, G.; Ivanov, V. G.; Faulques, E.; Sloan, J.; Smith, D. C. Raman Spectroscopy of Optical Transitions and Vibrational Energies of 1 nm HgTe Extreme Nanowires within Single Walled Carbon Nanotubes. ACS Nano 2014, 8, 9044– 9052,  DOI: 10.1021/nn5023632
      17
      Raman Spectroscopy of Optical Transitions and Vibrational Energies of ∼1 nm HgTe Extreme Nanowires within Single Walled Carbon Nanotubes
      Spencer, Joseph H.; Nesbitt, John M.; Trewhitt, Harrison; Kashtiban, Reza J.; Bell, Gavin; Ivanov, Victor G.; Faulques, Eric; Sloan, Jeremy; Smith, David C.
      ACS Nano (2014), 8 (9), 9044-9052CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      This paper presents a resonance Raman spectroscopy study of ∼1 nm diam. HgTe nanowires formed inside single walled carbon nanotubes by melt infiltration. Raman spectra have been measured for ensembles of bundled filled tubes, produced using tubes from two sep. sources, for excitation photon energies in the ranges 3.39-2.61 and 1.82-1.26 eV for Raman shifts down to ∼25 cm-1. We also present HRTEM characterization of the tubes and the results of DFT calcns. of the phonon and electronic dispersion relations, and the optical absorption spectrum based upon the obsd. structure of the HgTe nanowires. All of the evidence supports the hypothesis that the obsd. Raman features are not attributable to single walled carbon nanotubes, i.e., peaks due to radial breathing mode phonons, but are due to the HgTe nanowires. The obsd. addnl. features are due to four distinct phonons, with energies 47, 51, 94, and 115 cm-1, resp., plus their overtones and combinations. All of these modes have strong photon energy resonances that maximize at around 1.76 eV energy with respect to incident laser.
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    18. 18
      Shi, L.; Rohringer, P.; Suenaga, K.; Niimi, Y.; Kotakoski, J.; Meyer, J. C.; Peterlik, H.; Wanko, M.; Cahangirov, S.; Rubio, A.; Lapin, Z. J.; Novotny, L.; Ayala, P.; Pichler, T. Confined linear carbon chains as a route to bulk carbyne. Nat. Mater. 2016, 15, 634– 639,  DOI: 10.1038/nmat4617
      18
      Confined linear carbon chains as a route to bulk carbyne
      Shi, Lei; Rohringer, Philip; Suenaga, Kazu; Niimi, Yoshiko; Kotakoski, Jani; Meyer, Jannik C.; Peterlik, Herwig; Wanko, Marius; Cahangirov, Seymur; Rubio, Angel; Lapin, Zachary J.; Novotny, Lukas; Ayala, Paola; Pichler, Thomas
      Nature Materials (2016), 15 (6), 634-639CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)
      Strong chem. activity and extreme instability in ambient conditions characterize carbyne, an infinite sp1 hybridized carbon chain. As a result, much less has been explored about carbyne as compared to other carbon allotropes such as fullerenes, nanotubes and graphene. Although end-capping groups can be used to stabilize carbon chains, length limitations are still a barrier for prodn., and even more so for application. We report a method for the bulk prodn. of long acetylenic linear carbon chains protected by thin double-walled carbon nanotubes. The synthesis of very long arrangements is confirmed by a combination of transmission electron microscopy, X-ray diffraction and (near-field) resonance Raman spectroscopy. Our results establish a route for the bulk prodn. of exceptionally long and stable chains composed of more than 6,000 carbon atoms, representing an elegant forerunner towards the final goal of carbyne's bulk prodn.
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    19. 19
      Chambard, R.; Moreno-López, J. C.; Hermet, P.; Sato, Y.; Suenaga, K.; Pichler, T.; Jousselme, B.; Aznar, R.; Bantignies, J. L.; Izard, N.; Alvarez, L. Tuning of photoluminescence intensity and Fermi level position of individual single-walled carbon nanotubes by molecule confinement. Carbon 2022, 186, 423– 430,  DOI: 10.1016/j.carbon.2021.09.072
      19
      Tuning of photoluminescence intensity and Fermi level position of individual single-walled carbon nanotubes by molecule confinement
      Chambard, Romain; Moreno-Lopez, Juan Carlos; Hermet, Patrick; Sato, Yuta; Suenaga, Kazu; Pichler, Thomas; Jousselme, Bruno; Aznar, Raymond; Bantignies, Jean-Louis; Izard, Nicolas; Alvarez, Laurent
      Carbon (2022), 186 (), 423-430CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Photoluminescence of single-walled carbon nanotubes is monitored at the individual scale by mol. encapsulation into their hollow core. Depending on the electronic character (electron donor or acceptor) of the confined mol., enhancement or quenching of the photoluminescence intensity is demonstrated. This behavior is assigned to a charge transfer, evidenced by the shift of the Raman G-band, and a correlated Fermi level shift shown by photoemission expts. Our exptl. results are supported by DFT calcns. A consistent picture of the phys. interactions taking place in the hybrid systems and their effects on the optical and electronic properties is given. Our results indicate that the electron affinity or ionization potential of the encapsulated mols. and the diam. of the nanotube are relevant parameters to tune the light emission properties of the hybrid systems at the nanoscale.
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    20. 20
      Qu, H.; Rayabharam, A.; Wu, X.; Wang, P.; Li, Y.; Fagan, J.; Aluru, N. R.; Wang, Y. H. Selective filling of n-hexane in a tight nanopore. Nat. Commun. 2021, 12, 1– 8,  DOI: 10.1038/s41467-020-20587-1
      There is no corresponding record for this reference.
    21. 21
      Eliseev, A. A.; Yashina, L. V.; Verbitskiy, N. I.; Brzhezinskaya, M. M.; Kharlamova, M. V.; Chernysheva, M. V.; Lukashin, A. V.; Kiselev, N. A.; Kumskov, A. S.; Freitag, B.; Generalov, A. V.; Vinogradov, A. S.; Zubavichus, Y. V.; Kleimenov, E.; Nachtegaal, M. Interaction between single walled carbon nanotube and 1D crystal in CuX@SWCNT (X = Cl, Br, I) nanostructures. Carbon 2012, 50, 4021– 4039,  DOI: 10.1016/j.carbon.2012.04.046
      21
      Interaction between single walled carbon nanotube and 1D crystal in CuX@SWCNT (X = Cl, Br, I) nanostructures
      Eliseev, A. A.; Yashina, L. V.; Verbitskiy, N. I.; Brzhezinskaya, M. M.; Kharlamova, M. V.; Chernysheva, M. V.; Lukashin, A. V.; Kiselev, N. A.; Kumskov, A. S.; Freitag, B.; Generalov, A. V.; Vinogradov, A. S.; Zubavichus, Y. V.; Kleimenov, E.; Nachtegaal, M.
      Carbon (2012), 50 (11), 4021-4039CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      CuX@SWCNT (X = Cl, Br, I) nanostructures were prepd. by capillary filling of 1.4-1.6 nm single-walled carbon nanotubes (SWCNT) with copper halides. The structure of CuX@SWCNT (X = Cl, Br, I) represents a distorted two-layer hcp of halogen atoms arranged along the SWCNT. The EXAFS and the high angle angular dark field (HAADF) HRTEM data indicate that Cu is partially coordinated by C. According to the optical absorption, valence band photoemission spectroscopy and work function measurements, a Fermi level (FL) downshift as compared with the initial value for the nanotubes and a corresponding charge transfer from the nanotubes to the 1D crystals is obsd. for CuX@SWCNT nanostructures. The FL shift increases in the sequence CuI < CuBr < CuCl due to an increase of the electron affinity for the halogen atoms. The XPS data confirm the acceptor effect of copper halides and indicate that metallic and semiconducting nanotubes behave differently. Raman spectroscopy performed under electrochem. charging allowed estn. of the value of charge transfer between the nanotube walls and the intercalated 1D crystal. The X-ray absorption and emission spectra for carbon and copper thresholds revealed a new energy level composed of the carbon 2pz and copper 3d-orbitals. This indicates the Cu-C bonding, which in line with the structural HAADF HRTEM and EXAFS data.
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    22. 22
      Campo, J.; Piao, Y.; Lam, S.; Stafford, C. M.; Streit, J. K.; Simpson, J. R.; Hight Walker, A. R.; Fagan, J. A. Enhancing single-wall carbon nanotube properties through controlled endohedral filling. Nanoscale Horizons 2016, 1, 317– 324,  DOI: 10.1039/C6NH00062B
      22
      Enhancing single-wall carbon nanotube properties through controlled endohedral filling
      Campo, J.; Piao, Y.; Lam, S.; Stafford, C. M.; Streit, J. K.; Simpson, J. R.; Hight Walker, A. R.; Fagan, J. A.
      Nanoscale Horizons (2016), 1 (4), 317-324CODEN: NHAOAW; ISSN:2055-6764. (Royal Society of Chemistry)
      Chem. control of the endohedral vol. of single-wall carbon nanotubes (SWCNTs) via liq.-phase filling is established to be a facile strategy to controllably modify properties of SWCNTs in manners significant for processing and proposed applications. Encapsulation of over 20 different compds. with distinct chem. structures, functionalities, and effects is demonstrated in SWCNTs of multiple diam. ranges, with the ability to fill the endohedral vol. based on the availability of the core vol. and compatibility of the mol.'s size with the cross-section of the nanotube's cavity. Through exclusion of ingested water and selection of the endohedral chem. environment, significant improvements to the optical properties of dispersed SWCNTs such as narrowed optical transition linewidths and enhanced fluorescence intensities are obsd. Examples of tailoring modified properties towards applications or improved processing by endohedral passivation are discussed.
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    23. 23
      Burdanova, M. G.; Kashtiban, R. J.; Zheng, Y.; Xiang, R.; Chiashi, S.; Woolley, J. M.; Staniforth, M.; Sakamoto-Rablah, E.; Xie, X.; Broome, M.; Sloan, J.; Anisimov, A.; Kauppinen, E. I.; Maruyama, S.; Lloyd-Hughes, J. Ultrafast optoelectronic processes in 1d radial van der Waals heterostructures: Carbon, boron nitride, and MoS2 nanotubes with coexisting excitons and highly mobile charges. Nano Lett. 2020, 20, 3560– 3567,  DOI: 10.1021/acs.nanolett.0c00504
      23
      Ultrafast Optoelectronic Processes in 1D Radial van der Waals Heterostructures: Carbon, Boron Nitride, and MoS2 Nanotubes with Coexisting Excitons and Highly Mobile Charges
      Burdanova, Maria G.; Kashtiban, Reza J.; Zheng, Yongjia; Xiang, Rong; Chiashi, Shohei; Woolley, Jack Matthew; Staniforth, Michael; Sakamoto-Rablah, Emily; Xie, Xue; Broome, Matthew; Sloan, Jeremy; Anisimov, Anton; Kauppinen, Esko I.; Maruyama, Shigeo; Lloyd-Hughes, James
      Nano Letters (2020), 20 (5), 3560-3567CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Heterostructures built from 2D, atomically thin crystals are bound by the van der Waals force and exhibit unique optoelectronic properties. Here, we report the structure, compn. and optoelectronic properties of 1D van der Waals heterostructures comprising carbon nanotubes wrapped by atomically thin nanotubes of boron nitride and molybdenum disulfide (MoS2). The high quality of the composite was directly made evident on the at. scale by transmission electron microscopy, and on the macroscopic scale by a study of the heterostructure's equil. and ultrafast optoelectronics. Ultrafast pump-probe spectroscopy across the visible and terahertz frequency ranges identified that, in the MoS2 nanotubes, excitons coexisted with a prominent population of free charges. The electron mobility was comparable to that found in high-quality atomically thin crystals. The high mobility of the MoS2 nanotubes highlights the potential of 1D van der Waals heterostructures for nanoscale optoelectronic devices.
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    24. 24
      Burdanova, M. G.; Liu, M.; Staniforth, M.; Zheng, Y.; Xiang, R.; Chiashi, S.; Anisimov, A.; Kauppinen, E. I.; Maruyama, S.; Lloyd-Hughes, J. Intertube Excitonic Coupling in Nanotube Van der Waals Heterostructures. Adv. Funct. Mater. 2022, 32, 2104969,  DOI: 10.1002/adfm.202104969
      24
      Intertube Excitonic Coupling in Nanotube Van der Waals Heterostructures
      Burdanova, Maria G.; Liu, Ming; Staniforth, Michael; Zheng, Yongjia; Xiang, Rong; Chiashi, Shohei; Anisimov, Anton; Kauppinen, Esko I.; Maruyama, Shigeo; Lloyd-Hughes, James
      Advanced Functional Materials (2022), 32 (11), 2104969CODEN: AFMDC6; ISSN:1616-301X. (Wiley-VCH Verlag GmbH & Co. KGaA)
      Strong intertube excitonic coupling is demonstrated in 1D van der Waals heterostructures by examg. the ultrafast response of radial C/BN/MoS2 core/shell/skin nanotubes to femtosecond IR light pulses. Remarkably, IR excitation of excitons in the semiconducting carbon nanotubes (CNTs) creates a prominent excitonic response in the visible range from the MoS2 skin, even with IR photons at energies well below the bandgap of MoS2. Via classical analogies and a quantum model of the light-matter interaction these findings are assigned to intertube excitonic correlations. Dipole-dipole Coulomb interactions in the coherent regime produce intertube biexcitons, which persist for tens of femtoseconds, while on longer timescales (>100 ps) hole tunneling-from the CNT core, through the BN tunnel barrier, to the MoS2 skin-creates intertube excitons. Charge transfer and dipole-dipole interactions thus play prominent roles on different timescales, and establish new possibilities for the multi-functional use of these new nanoscale coaxial cables.
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    25. 25
      Liu, H.; Nishide, D.; Tanaka, T.; Kataura, H. Large-scale single-chirality separation of single-wall carbon nanotubes by simple gel chromatography. Nat. Commun. 2011, 2, 1– 8,  DOI: 10.1038/ncomms1313
      25
      An optimized small molecule inhibitor cocktail supports long-term maintenance of human embryonic stem cells
      Tsutsui, Hideaki; Valamehr, Bahram; Hindoyan, Antreas; Qiao, Rong; Ding, Xianting; Guo, Shuling; Witte, Owen N.; Liu, Xin; Ho, Chih-Ming; Wu, Hong
      Nature Communications (2011), 2 (Jan.), 1-8, 8 pp.CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      A major challenge in stem cell-mediated regenerative medicine is the development of defined culture systems for the maintenance of clin.-grade human embryonic stem (hES) cells. Here, we identify, using a feedback system control scheme, a unique combination of three small mol. inhibitors that enables the maintenance of hES cells on a fibronectin-coated surface through single cell passaging. After 20 passages, the undifferentiated state of the hES cells was confirmed by OCT4, SSEA4 and NANOG expressions, whereas their pluripotent potential and genetic integrity were demonstrated by teratoma formation and normal karyotype, resp. Our study attests to the power of the feedback system control scheme to quickly pinpoint optimal conditions for desired biol. activities, and provides a chem. defined, scalable and single cell passaging culture system for hES cells.
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    26. 26
      Tu, X.; Manohar, S.; Jagota, A.; Zheng, M. DNA sequence motifs for structure-specific recognition and separation of carbon nanotubes. Nature 2009, 460, 250– 253,  DOI: 10.1038/nature08116
      26
      DNA sequence motifs for structure-specific recognition and separation of carbon nanotubes
      Tu, Xiaomin; Manohar, Suresh; Jagota, Anand; Zheng, Ming
      Nature (London, United Kingdom) (2009), 460 (7252), 250-253CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Single-walled carbon nanotubes (SWNTs) are a family of mols. that have the same cylindrical shape but different chiralities. Many fundamental studies and technol. applications of SWNTs require a population of tubes with identical chirality that current syntheses cannot provide. The SWNT sorting problem - i.e., sepn. of a synthetic mixt. of tubes into individual single-chirality components - has attracted considerable attention in recent years. Intense efforts so far have focused largely on, and resulted in solns. for, a weaker version of the sorting problem: metal/semiconductor sepn. A systematic and general method to purify each and every single-chirality species of the same electronic type from the synthetic mixt. of SWNTs is highly desirable, but the task proved to be insurmountable to date. Here the authors report such a method, which allows purifn. of all 12 major single-chirality semiconducting species from a synthetic mixt., with sufficient yield for both fundamental studies and application development. The authors have designed an effective search of a DNA library of ∼1060 in size, and have identified >20 short DNA sequences, each of which recognizes and enables chromatog. purifn. of a particular nanotube species from the synthetic mixt. Recognition sequences exhibit a periodic purine-pyrimidines pattern, which can undergo hydrogen-bonding to form a two-dimensional sheet, and fold selectively on nanotubes into a well-ordered three-dimensional barrel. Probably the ordered two-dimensional sheet and three-dimensional barrel provide the structural basis for the obsd. DNA recognition of SWNTs.
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    27. 27
      Ghosh, S.; Bachilo, S. M.; Weisman, R. B. Advanced sorting of single-walled carbon nanotubes by nonlinear density-gradient ultracentrifugation. Nat. Nanotechnol. 2010, 5, 443– 450,  DOI: 10.1038/nnano.2010.68
      27
      Advanced sorting of single-walled carbon nanotubes by nonlinear density-gradient ultracentrifugation
      Ghosh, Saunab; Bachilo, Sergei M.; Weisman, R. Bruce
      Nature Nanotechnology (2010), 5 (6), 443-450CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
      Existing methods for growing single-walled carbon nanotubes produce samples with a range of structures and electronic properties, but many potential applications require pure nanotube samples. D.-gradient ultracentrifugation has recently emerged as a technique for sorting as-grown mixts. of single-walled nanotubes into their distinct (n,m) structural forms, but to date this approach is limited to samples contg. only a small no. of nanotube structures, and has often required repeated d.-gradient ultracentrifugation processing. Here, it is reported that the use of tailored nonlinear d. gradients can significantly improve d.-gradient ultracentrifugation sepns. It is shown that highly polydisperse samples of single-walled nanotubes grown by the HiPco method are readily sorted in a single step to give fractions enriched in any of ten different (n,m) species. Furthermore, minor variants of the method allow sepn. of the mirror-image isomers (enantiomers) of seven (n,m) species. Optimization of this approach was aided by the development of instrumentation that spectroscopically maps nanotube contents inside undisturbed centrifuge tubes.
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    28. 28
      Arnold, M. S.; Green, A. A.; Hulvat, J. F.; Stupp, S. I.; Hersam, M. C. Sorting carbon nanotubes by electronic structure using density differentiation. Nat. Nanotechnol. 2006, 1, 60– 65,  DOI: 10.1038/nnano.2006.52
      28
      Sorting carbon nanotubes by electronic structure using density differentiation
      Arnold, Michael S.; Green, Alexander A.; Hulvat, James F.; Stupp, Samuel I.; Hersam, Mark C.
      Nature Nanotechnology (2006), 1 (1), 60-65CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)
      The heterogeneity of as-synthesized single-walled carbon nanotubes (SWNTs) precludes their widespread application in electronics, optics and sensing. The authors report on the sorting of carbon nanotubes by diam., bandgap and electronic type using structure-discriminating surfactants to engineer subtle differences in their buoyant densities. Using the scalable technique of d.-gradient ultracentrifugation, the authors have isolated narrow distributions of SWNTs in which >97% are within a 0.02-nm-diam. range. Also, using competing mixts. of surfactants, the authors produced bulk quantities of SWNTs of predominantly a single electronic type. These materials were used to fabricate thin-film elec. devices of networked SWNTs characterized by either metallic or semiconducting behavior.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtFCisrvF&md5=4cc068399931940846573a7e9cf79873
    29. 29
      Fagan, J. A.; Huh, J. Y.; Simpson, J. R.; Blackburn, J. L.; Holt, J. M.; Larsen, B. A.; Walker, A. R. Separation of empty and water-filled single-wall carbon nanotubes. ACS Nano 2011, 5, 3943– 3953,  DOI: 10.1021/nn200458t
      29
      Separation of Empty and Water-Filled Single-Wall Carbon Nanotubes
      Fagan, Jeffrey A.; Huh, Ji Yeon; Simpson, Jeffrey R.; Blackburn, Jeffrey L.; Holt, Josh M.; Larsen, Brian A.; Hight Walker, Angela R.
      ACS Nano (2011), 5 (5), 3943-3953CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      The sepn. of empty and water-filled laser ablation and elec. arc synthesized nanotubes is reported. Centrifugation of these large-diam. nanotubes dispersed with sodium deoxycholate using specific conditions produces isolated bands of empty and water-filled nanotubes without significant diam. selection. This sepn. is consistent across multiple nanotube populations dispersed from different source soots. Detailed spectroscopic characterization of the resulting empty and filled fractions reveals that water filling leads to systematic changes to the optical and vibrational properties. Also, sequential sepn. of the resolved fractions using cosurfactants and d. gradient ultracentrifugation reveals that water filling strongly influences the optimal conditions for metallic and semiconducting sepn.
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    30. 30
      Yang, X.; Liu, T.; Li, R.; Yang, X.; Lyu, M.; Fang, L.; Zhang, L.; Wang, K.; Zhu, A.; Zhang, L.; Qiu, C.; Zhang, Y. Z.; Wang, X.; Peng, L. M.; Yang, F.; Li, Y. Host-Guest Molecular Interaction Enabled Separation of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes. J. Am. Chem. Soc. 2021, 143, 10120– 10130,  DOI: 10.1021/jacs.1c02245
      30
      Host-Guest Molecular Interaction Enabled Separation of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes
      Yang, Xusheng; Liu, Tianhui; Li, Ruoming; Yang, Xiaoxin; Min, Lyu; Fang, Li; Zhang, Lei; Wang, Kun; Zhu, Anquan; Zhang, Luyao; Qiu, Chenguang; Zhang, Yuan-Zhu; Wang, Xiao; Peng, Lian-Mao; Yang, Feng; Li, Yan
      Journal of the American Chemical Society (2021), 143 (27), 10120-10130CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a diam. of around 1.0-1.5 nm, which present bandgaps comparable to silicon, are highly desired for electronic applications. Therefore, the prepn. of s-SWCNTs of such diams. has been attracting great attention. The inner surface of SWCNTs has a suitable curvature and large contacting area, which is attractive in host-guest chem. triggered by electron transfer. Here we reported a strategy of host-guest mol. interaction between SWCNTs and inner clusters with designed size, thus selectively sepg. s-SWCNTs of expected diams. When polyoxometalate clusters of ~ 1 nm in size were filled in the inner cavities of SWCNTs, s-SWCNTs with diams. concd. at ~ 1.3-1.4 nm were selectively extd. with the purity of ~ 98% by a com. available polyfluorene deriv. The field-effect transistors built from the sorted s-SWCNTs showed a typical behavior of semiconductors. The sorting mechanisms assocd. with size-dependent electron transfer from nanotubes to inner polyoxometalate were revealed by the spectroscopic and in situ electron microscopic evidence as well as the theor. calcn. The polyoxometalates with designable size and redox property enable the flexible regulation of interaction between the nanotubes and the clusters, thus tuning the diam. of sorted s-SWCNTs. The present sorting strategy is simple and should be generally feasible in other SWCNT sorting techniques, bringing both great easiness in dispersant design and improved selectivity.
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    31. 31
      White, C. T.; Robertson, D. H.; Mintmire, J. W. Helical and rotational symmetries of nanoscale graphitic tubules. Phys. Rev. B 1993, 47, 5485,  DOI: 10.1103/PhysRevB.47.5485
      31
      Helical and rotational symmetries of nanoscale graphitic tubules
      White, C. T.; Robertson, D. H.; Mintmire, J. W.
      Physical Review B: Condensed Matter and Materials Physics (1993), 47 (9), 5485-8CODEN: PRBMDO; ISSN:0163-1829.
      The authors show how all extended graphitic tubules constructed by rolling up a single graphite sheet can be defined in terms of their helical and rotational symmetries. Specification of these symmetries is practically mandatory in all but the simplest calcns. of tubule properties as a function of radius and structure. The authors also report results of a tight-binding study implemented by using these symmetries. Independent of their helicity the larger-diam., moderate-band-gap semiconducting tubules all have band gaps given approx. by Eg = |V0|(d0/RT), where RT is the tubule radius and V0 is the hopping matrix element between nearest-neighboring 2p orbitals oriented normal to the tubule surface and centered on C atoms sepd. by a distance d0 along this surface. All tubules constructed by rolling up the graphite sheet can be labeled in a fashion familiar in the description of helical chain polymers with translational symmetry.
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    32. 32
      Sato, K.; Saito, R.; Jiang, J.; Dresselhaus, G.; Dresselhaus, M. S. Discontinuity in the family pattern of single-wall carbon nanotubes. Physical Review B - Condensed Matter and Materials Physics 2007, 76, 195446,  DOI: 10.1103/PhysRevB.76.195446
      32
      Discontinuity in the family pattern of single-wall carbon nanotubes
      Sato, K.; Saito, R.; Jiang, J.; Dresselhaus, G.; Dresselhaus, M. S.
      Physical Review B: Condensed Matter and Materials Physics (2007), 76 (19), 195446/1-195446/7CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      The higher lying bright exciton energies (EM11,ES33,ES44,EM22,ES55,ES66,EM33) of single-wall C nanotubes are calcd. by solving the Bethe-Salpeter equation within an extended tight binding method. For smaller diam. nanotubes, some higher Eii excitonic states are missing. In particular, some Eii's on the 1-dimensional Brillouin zone (cutting line) are no longer relevant to the formation of excitons and are skipped in listing the order of the Eii values. Thus the family patterns show some discontinuities in k space and this effect should be observable in Raman G' band spectroscopy. The higher exciton energies ES33 and ES44 have a large chirality dependence due to many body effects, since the self-energy becomes larger than the binding energy. Thus the chirality dependence of the higher Eii comes not only from a single particle energy but also from many-body effects.
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    33. 33
      Yang, L.; Han, J. Electronic structure of deformed carbon nanotubes. Phys. Rev. Lett. 2000, 85, 154,  DOI: 10.1103/PhysRevLett.85.154
      33
      Electronic Structure of Deformed Carbon Nanotubes
      Yang, Liu; Han, Jie
      Physical Review Letters (2000), 85 (1), 154-157CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Electronic structure of deformed carbon nanotubes varies widely depending on their chirality and deformation mode. We present a framework to analyze these variations by quantifying the dispersion relation and d. of states. The theory is based on the Huckel tight-binding model and confirmed by four orbital tight-binding simulations of nanotubes under stretching, compression, torsion, and bending. It unriddles and unifies previous band gap studies and predicts the shifting, merging, and splitting of Van Hove singularities in the d. of state, and the zigzag pattern of band gap change with strains. Possible applications to nanotube devices and spectroscopy research are also presented.
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    34. 34
      Arnold, K.; Lebedkin, S.; Kiowski, O.; Hennrich, F.; Kappes, M. M. Matrix-Imposed Stress-Induced Shifts in the Photoluminescence of Single-Walled Carbon Nanotubes at Low Temperatures. Nano Lett. 2004, 4, 2349– 2354,  DOI: 10.1021/nl048630c
      34
      Matrix-Imposed Stress-Induced Shifts in the Photoluminescence of Single-Walled Carbon Nanotubes at Low Temperatures
      Arnold, Katharina; Lebedkin, Sergei; Kiowski, Oliver; Hennrich, Frank; Kappes, Manfred M.
      Nano Letters (2004), 4 (12), 2349-2354CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Photoluminescence spectra of H2O-surfactant dispersions of semiconducting single-walled C nanotubes (SWNTs) show large shifts of interband transition energies upon freezing and cooling the dispersions to 16 K. This is accompanied by an increase of the emission intensities up to ∼10 times in the presence of poly(vinylpyrrolidone). The shifts develop mainly in the temp. interval of ∼100-240 K and are reversible by cycling the temp. Two groups of nanotubes classified by the value of (n-m) mod 3, where n,m are structure indexes, demonstrate opposite shifts, the largest ones from nanotubes with small chiral angles. The exptl. data agree well with calcns. of Yang et al. [Phys. Rev. B 1999, 60, 13874] for SWNTs under axial compression and indicate that large stresses of up to ∼5 GPa are generated in individual nanotubes by thermal contraction of the ice matrix.
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    35. 35
      Karaiskaj, D.; Engtrakul, C.; McDonald, T.; Heben, M. J.; Mascarenhas, A. Intrinsic and extrinsic effects in the temperature-dependent photoluminescence of semiconducting carbon nanotubes. Phys. Rev. Lett. 2006, 96, 106805,  DOI: 10.1103/PhysRevLett.96.106805
      35
      Intrinsic and Extrinsic Effects in the Temperature-Dependent Photoluminescence of Semiconducting Carbon Nanotubes
      Karaiskaj, D.; Engtrakul, C.; McDonald, T.; Heben, M. J.; Mascarenhas, A.
      Physical Review Letters (2006), 96 (10), 106805/1-106805/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      The temp. dependence of the band gap of semiconducting C nanotubes was measured for ten different nanotube species. The unprecedented effectiveness in avoiding the effect of external strain, or any other effects originating from the surrounding environment, lead to an accurate measurement of the band gap temp. dependence, giving fundamental insight into the nanotube electron-phonon interaction. Small but reproducible energy shifts of the emission lines with temp. were obsd., showing a moderate chirality dependence, well in agreement with recent theor. calcns. In addn. to the energy shift, a substantial narrowing of the emission lines was also obsd. The removal of the temp. shift of the band gap allows the precise measurement of the effect of external strain on C nanotubes in different environments.
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    36. 36
      Eliseev, A. A.; Yashina, L. V.; Brzhezinskaya, M. M.; Chernysheva, M. V.; Kharlamova, M. V.; Verbitsky, N. I.; Lukashin, A. V.; Kiselev, N. A.; Kumskov, A. S.; Zakalyuhin, R. M.; Hutchison, J. L.; Freitag, B.; Vinogradov, A. S. Structure and electronic properties of AgX (X = Cl, Br, I)-intercalated single-walled carbon nanotubes. Carbon 2010, 48, 2708– 2721,  DOI: 10.1016/j.carbon.2010.02.037
      36
      Structure and electronic properties of AgX (X = Cl, Br, I)-intercalated single-walled carbon nanotubes
      Eliseev, A. A.; Yashina, L. V.; Brzhezinskaya, M. M.; Chernysheva, M. V.; Kharlamova, M. V.; Verbitsky, N. I.; Lukashin, A. V.; Kiselev, N. A.; Kumskov, A. S.; Zakalyuhin, R. M.; Hutchison, J. L.; Freitag, B.; Vinogradov, A. S.
      Carbon (2010), 48 (10), 2708-2721CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      One-dimensional Ag halide crystals were grown within single-walled nanotube (SWCNT) channels from the melt using a molten media method. Atomic structures of the AgX@SWCNT hybrids are proposed based on high-resoln. TEM images. AgCl intercalation results in amorphous filling of the SWCNT channels. 1-dimensional AgBr and AgI crystals intercalated into 1.34 nm SWCNTs possess the structure of a two-layer hcp. of halogen atoms arranged laterally with respect to the SWCNT axis. Electronic properties and chem. bonding in AgX@SWNTs were studied by high-resoln. x-ray photoelectron and near edge X-ray absorption fine structure spectroscopy (BESSY, Germany), optical absorption and Raman spectroscopy. Optical absorption spectroscopy indicates disappearance of E11S transitions between van-Hove singularities, which is caused by an effective electron exchange between AgX and the SWCNT. C 1s x-ray absorption spectra indicate a new empty level (S1) induced by charge transfer. Multi-component structure of photoemission spectra can be explained both by the variation of the work function of AgX@SWCNT hybrids and local interactions between halogen ions and C atoms. Raman spectroscopy performed under electrochem. charging clearly and directly demonstrated the acceptor behavior of AgX with respect to SWCNTs. Based on a whole dataset, a self-consistent picture of the AgX-SWCNT interactions is derived.
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    37. 37
      Campo, J.; Cambré, S.; Botka, B.; Obrzut, J.; Wenseleers, W.; Fagan, J. A. Optical Property Tuning of Single-Wall Carbon Nanotubes by Endohedral Encapsulation of a Wide Variety of Dielectric Molecules. ACS Nano 2021, 15, 2301– 2317,  DOI: 10.1021/acsnano.0c08352
      37
      Optical Property Tuning of Single-Wall Carbon Nanotubes by Endohedral Encapsulation of a Wide Variety of Dielectric Molecules
      Campo, Jochen; Cambre, Sofie; Botka, Bea; Obrzut, Jan; Wenseleers, Wim; Fagan, Jeffrey A.
      ACS Nano (2021), 15 (2), 2301-2317CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      Specific and tunable modification to the optical properties of single-wall carbon nanotubes (SWCNTs) is demonstrated through direct encapsulation into the nanotube interior of guest mols. with widely varying static dielec. consts. Filled through simple ingestion of the guest mol., each SWCNT population is demonstrated to display a robust modification to absorbance, fluorescence, and Raman spectra. Over 30 distinct compds., covering static dielec. consts. from 1.8 to 109, are inserted in large diam. SWCNTs (d = 1.104-1.524 nm) and more than 10 compds. in small diam. SWCNTs (d = 0.747-1.153 nm), demonstrating that the general effect of filler dielec. on the nanotube optical properties is a monotonic energy redn. (red-shifting) of the optical transitions with increased magnitude of the dielec. const. Systematic fitting of the two-dimensional fluorescence-excitation and Raman spectra addnl. enables detn. of the crit. filling diam. for each mol. and distinguishing of overall trends from specific guest-host interactions. Comparisons to predictions from existing theory are presented, and specific guest mol./SWCNT chirality combinations that disobey the general trend and theory are identified. A general increase of the fluorescence intensity and line narrowing is obsd. for low dielec. consts., with long linear alkane filled SWCNTs exhibiting emission intensities approaching those of empty SWCNTs. These results demonstrate an exploitable modulation in the optical properties of SWCNTs and provide a foundation for examg. higher-order effects, such as due to nonbulk-like mol. stacking, in host-guest interactions in well-controlled nanopore size materials.
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    38. 38
      Mehlenbacher, R. D.; McDonough, T. J.; Grechko, M.; Wu, M.-Y.; Arnold, M. S.; Zanni, M. T. Energy transfer pathways in semiconducting carbon nanotubes revealed using two-dimensional white-light spectroscopy. Nat. Commun. 2015, 6, 6732,  DOI: 10.1038/ncomms7732
      38
      Energy transfer pathways in semiconducting carbon nanotubes revealed using two-dimensional white-light spectroscopy
      Mehlenbacher, Randy D.; McDonough, Thomas J.; Grechko, Maksim; Wu, Meng-Yin; Arnold, Michael S.; Zanni, Martin T.
      Nature Communications (2015), 6 (), 6732CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Thin film networks of highly purified semiconducting carbon nanotubes (CNTs) are being explored for energy harvesting and optoelectronic devices because of their exceptional transport and optical properties. The nanotubes in these films are in close contact, which permits energy to flow through the films, although the pathways and mechanisms for energy transfer are largely unknown. Here we use a broadband continuum to collect femtosecond two-dimensional white-light spectra. The continuum spans 500 to 1,300 nm, resolving energy transfer between all combinations of bandgap (S1) and higher (S2) transitions. We observe ultrafast energy redistribution on the S2 states, non-Forster energy transfer on the S1 states and anti-correlated energy levels. The two-dimensional spectra reveal competing pathways for energy transfer, with S2 excitons taking routes depending on the bandgap sepn., whereas S1 excitons relax independent of the bandgap. These observations provide a basis for understanding and ultimately controlling the photophysics of energy flow in CNT-based devices.
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    39. 39
      Christie, A. B.; Sutherland, I.; Walls, J. M. Studies of the composition, ion-induced reduction and preferential sputtering of anodic oxide films on Hg0.8Cd0.2Te by XPS. Surf. Sci. 1983, 135, 225– 242,  DOI: 10.1016/0039-6028(83)90220-0
      39
      Studies of the composition, ion-induced reduction and preferential sputtering of anodic oxide films on mercury cadmium telluride (Hg0.8Cd0.2Te) by XPS
      Christie, A. B.; Sutherland, I.; Walls, J. M.
      Surface Science (1983), 135 (1-3), 225-42CODEN: SUSCAS; ISSN:0039-6028.
      Angle-resolved studies of anodic oxide films on Hg0.8Cd0.2Te (CMT), and on Cd and Te bulk oxides, by XPS revealed the formation of a discrete altered overlayer, contg. reduced Te (Te0) species, following inert gas ion bombardment. In the presence of Cd2+ species, recombination occurs yielding a Te2- (telluride) species, in the form of CdTe. Only Te2- formation is obsd. on ion-induced redn. of CdTeO3, whereas there is no evidence for significant Te2- formation on either TeO2 or anodic oxides on CMT, reflecting the low Cd content of these latter 2 oxides. In addn., preferential cation sputtering leads to a homogeneous (within the XPS sampling depth) Te4+-depleted layer in Cd-Te mixed oxides. The phenomenon is characterized by an effective sputter yield ratio (STe4+/SCd2+) of 1.83 (±0.06). The anodic oxide on CMT, when cor. for preferential Te4+ sputtering, yields a (Te4+):(Cd2+) ratio of 4.6 (±0.5), in excellent agreement with the bulk Te:Cd ratio in Hg0.8Cd0.2Te. An anodic oxide film compn. of approx. <25 mol % CdTe2O5 and >75 mol % TeO2 and/or mixed Hg-Te oxides is proposed.
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    40. 40
      Leech, P. W.; Gwynn, P. J.; Kibel, M. H. A selective etchant for Hg1–xCdx Te, CdTe and HgTe on GaAs. Appl. Surf. Sci. 1989, 37, 291– 298,  DOI: 10.1016/0169-4332(89)90491-1
      40
      A selective etchant for mercury cadmium telluride, cadmium telluride, and mercury telluride on gallium arsenide
      Leech, P. W.; Gwynn, P. J.; Kibel, M. H.
      Applied Surface Science (1989), 37 (3), 291-8CODEN: ASUSEE; ISSN:0169-4332.
      A new etchant (KI:I:HBr) for Hg1-xCdxTe, HgTe, and CdTe is developed which is selective in its action with respect to GaAs. The characteristics of the etchant were examd. using MOCVD grown layers on 2° misoriented (100) GaAs substrates with a 0.4 μm CdTe buffer layer. Measurements of the etch rate of the layers give ratios for Hg0.6Cd0.4Te:GaAs of 290:1, for CdTe:GaAs of 273.1 and for HgTe:GaAs of 360:1. In addn., quant. analyses of the layers by XPS were used to compare the surface compositional effects of KI:I:HBr in relation to the Br based etchant, 0.1% (wt./wt.) Br:HBr.
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    41. 41
      Zhang, Z.; Wang, B.; Zhou, P.; Guo, D.; Kang, R.; Zhang, B. A novel approach of chemical mechanical polishing using environment-friendly slurry for mercury cadmium telluride semiconductors. Sci. Rep. 2016, 6, 22466,  DOI: 10.1038/srep22466
      41
      A novel approach of chemical mechanical polishing using environment-friendly slurry for mercury cadmium telluride semiconductors
      Zhang, Zhenyu; Wang, Bo; Zhou, Ping; Guo, Dongming; Kang, Renke; Zhang, Bi
      Scientific Reports (2016), 6 (), 22466CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      A novel approach of chem. mech. polishing (CMP) is developed for mercury cadmium telluride (HgCdTe or MCT) semiconductors. Firstly, fixed-abrasive lapping is used to machine the MCT wafers, and the lapping soln. is deionized water. Secondly, the MCT wafers are polished using the developed CMP slurry. The CMP slurry consists of mainly SiO2 nanospheres, H2O2, and malic and citric acids, which are different from previous CMP slurries, in which corrosive and toxic chem. reagents are usually employed. Finally, the polished MCT wafers are cleaned and dried by deionized water and compressed air, resp. The novel approach of CMP is environment-friendly. Surface roughness Ra, and peak-to-valley (PV) values of 0.45, and 4.74 nm are achieved, resp. on MCT wafers after CMP. The first and second passivating processes are obsd. in electrochem. measurements on MCT wafers. The fundamental mechanisms of CMP are proposed according to the XPS and electrochem. measurements. Malic and citric acids dominate the first passivating process, and the CMP slurry governs the second process. Te4+3d peaks are absent after CMP induced by the developed CMP slurry, indicating the removing of oxidized films on MCT wafers, which is difficult to achieve using single H2O2 and malic and citric acids solns.
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    42. 42
      Hutson, N. D.; Attwood, B. C.; Scheckel, K. G. XAS and XPS Characterization of Mercury Binding on Brominated Activated Carbon. Environ. Sci. Technol. 2007, 41, 1747– 1752,  DOI: 10.1021/es062121q
      42
      XAS and XPS Characterization of Mercury Binding on Brominated Activated Carbon
      Hutson, Nick D.; Attwood, Brian C.; Scheckel, Kirk G.
      Environmental Science & Technology (2007), 41 (5), 1747-1752CODEN: ESTHAG; ISSN:0013-936X. (American Chemical Society)
      Brominated powd. activated carbon sorbents have been shown to be quite effective for mercury capture when injected into the flue gas duct at coal-fired power plants and are esp. useful when burning Western US low-chlorine subbituminous coals. X-ray absorption spectroscopy (XAS) and XPS have been used to det. information about the speciation and binding of mercury on two com. available brominated activated carbons. The results are compared with similar anal. of a conventional (nonhalogenated) and chlorinated activated carbon. Both the XAS and XPS results indicate that the mercury, though introduced as elemental vapor, is consistently bound on the carbon in the oxidized form. The conventional and chlorinated activated carbons appeared to contain mercury bound to chlorinated sites and possibly to sulfate species that have been incorporated onto the carbon from adsorbed SO2. The mercury-contg. brominated sorbents appear to contain mercury bound primarily at bromination sites. The mechanism of capture for the sorbents likely consists of surface-enhanced oxidn. of the elemental mercury vapor via interaction with surface-bound halide species with subsequent binding by surface halide or sulfate species.
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    43. 43
      Qiao, S.; Chen, J.; Li, J.; Qu, Z.; Liu, P.; Yan, N.; Jia, J. Adsorption and Catalytic Oxidation of Gaseous Elemental Mercury in Flue Gas over MnOx/Alumina. Ind. Eng. Chem. Res. 2009, 48, 3317– 3322,  DOI: 10.1021/ie801478w
      43
      Adsorption and Catalytic Oxidation of Gaseous Elemental Mercury in Flue Gas over MnOx/Alumina
      Qiao, Shaohua; Chen, Jie; Li, Jianfeng; Qu, Zan; Liu, Ping; Yan, Naiqiang; Jia, Jinping
      Industrial & Engineering Chemistry Research (2009), 48 (7), 3317-3322CODEN: IECRED; ISSN:0888-5885. (American Chemical Society)
      MnOx/Al2O3 catalysts (i.e., impregnating Al2O3 with MnOx) were used to remove elemental Hg from flue gas. MnOx/Al2O3 had significant adsorption performance for Hg capture in the absence of HCl; its favorable adsorption temp. was ∼600° K. However, catalytic oxidn. of Hg became dominant when HCl or Cl2 was present in flue gas; Hg removal efficiency was ≤90% with 20 ppm HCl or 2 ppm Cl2. Also, the catalysts with adsorbed Hg could be chem. regenerated by rinsing with HCl gas to strip off adsorbed Hg as HgCl2. SO2 inhibited Hg adsorption by the catalysts, but this inhibition was less than the catalytic oxidn. of Hg, esp. in the presence of Cl2. XPS and pyrolysis at. absorption spectroscopy anal. results indicated the adsorbed Hg was mainly in the form of mercuric oxide (HgO); the weakly-bonded speciation and their ratio varied with the amt. adsorbed and catalyst Mn content. Multi-functional performance of MnOx/Al2O3 for flue gas Hg removal appeared promising for industrial applications.
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    44. 44
      Araujo, P. T.; Doorn, S. K.; Kilina, S.; Tretiak, S.; Einarsson, E.; Maruyama, S.; Chacham, H.; Pimenta, M. A.; Jorio, A. Third and Fourth Optical Transitions in Semiconducting Carbon Nanotubes. Phys. Rev. Lett. 2007, 98, 067401,  DOI: 10.1103/PhysRevLett.98.067401
      44
      Third and Fourth Optical Transitions in Semiconducting Carbon Nanotubes
      Araujo, Paulo T.; Doorn, Stephen K.; Kilina, Svetlana; Tretiak, Sergei; Einarsson, Erik; Maruyama, Shigeo; Chacham, Helio; Pimenta, Marcos A.; Jorio, Ado
      Physical Review Letters (2007), 98 (6), 067401/1-067401/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      The authors have studied the optical transition energies of single-wall C nanotubes over broad diam. (0.7-2.3 nm) and energy (1.26-2.71 eV) ranges, using their radial breathing mode Raman spectra. The authors establish the diam. and chiral angle dependence of the poorly studied 3rd and 4th optical transitions in semiconducting tubes. Comparative anal. between the higher lying transitions and the 1st and 2nd transitions show 2 different diam. scalings. Quantum mech. calcns. explain the result showing strongly bound excitons in the 1st and 2nd transitions and a delocalized electron wave function in the 3rd transition.
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    45. 45
      Lloyd-Hughes, J.; Jeon, T.-I. A Review of the Terahertz Conductivity of Bulk and Nano-Materials. Journal of Infrared Millimeter and Terahertz Waves 2012, 33, 871,  DOI: 10.1007/s10762-012-9905-y
      45
      A Review of the Terahertz Conductivity of Bulk and Nano-Materials
      Lloyd-Hughes, James; Jeon, Tae-In
      Journal of Infrared, Millimeter, and Terahertz Waves (2012), 33 (9), 871-925CODEN: JIMTC4; ISSN:1866-6892. (Springer)
      We review pioneering and recent studies of the cond. of solid state systems at terahertz frequencies. A variety of theor. formalisms that describe the terahertz cond. of bulk, mesoscopic and nanoscale materials are outlined, and their validity and limitations are given. Exptl. highlights are discussed from studies of inorg. semiconductors, org. materials (such as graphene, carbon nanotubes and polymers), metallic films and strongly correlated electron systems including superconductors.
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    46. 46
      Burdanova, M. G.; Tsapenko, A. P.; Kharlamova, M. V.; Kauppinen, E. I.; Gorshunov, B. P.; Kono, J.; Lloyd-Hughes, J. A Review of the Terahertz Conductivity and Photoconductivity of Carbon Nanotubes and Heteronanotubes. Advanced Optical Materials 2021, 9, 2101042,  DOI: 10.1002/adom.202101042
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      A Review of the Terahertz Conductivity and Photoconductivity of Carbon Nanotubes and Heteronanotubes
      Burdanova, Maria G.; Tsapenko, Alexey P.; Kharlamova, Marianna V.; Kauppinen, Esko I.; Gorshunov, Boris P.; Kono, Junichiro; Lloyd-Hughes, James
      Advanced Optical Materials (2021), 9 (24), 2101042CODEN: AOMDAX; ISSN:2195-1071. (Wiley-VCH Verlag GmbH & Co. KGaA)
      A review. Terahertz (THz) spectroscopy is an ideal non-contact and non-destructive technique that probes the elec. cond. of nanomaterials. This presents the current status of research in the THz properties of quasi-1D materials, such as nanotubes (NTs) and NT heterostructures. The detailed description of THz exptl. methods (THz time-domain spectroscopy, optical pump-THz probe spectroscopy) and cond. extn. methods are presented along with the phys. models (Drude, plasmon, effective medium theories, etc.) supporting them. Optoelectronic applications, such as optical modulators, switches, and shielding devices, are discussed and illustrate a bright future for these materials.
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    47. 47
      Fagan, J. A.; Hároz, E. H.; Ihly, R.; Gui, H.; Blackburn, J. L.; Simpson, J. R.; Lam, S.; Hight Walker, A. R.; Doorn, S. K.; Zheng, M. Isolation of > 1 nm diameter single-wall carbon nanotube species using aqueous two-phase extraction. ACS Nano 2015, 9, 5377– 5390,  DOI: 10.1021/acsnano.5b01123
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      Isolation of >1 nm Diameter Single-Wall Carbon Nanotube Species Using Aqueous Two-Phase Extraction
      Fagan, Jeffrey A.; Haroz, Erik H.; Ihly, Rachelle; Gui, Hui; Blackburn, Jeffrey L.; Simpson, Jeffrey R.; Lam, Stephanie; Hight Walker, Angela R.; Doorn, Stephen K.; Zheng, Ming
      ACS Nano (2015), 9 (5), 5377-5390CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      In this contribution we demonstrate the effective sepn. of single-wall carbon nanotube (SWCNT) species with diams. larger than 1 nm through multistage aq. two-phase extn. (ATPE), including isolation at the near-monochiral species level up to at least the diam. range of SWCNTs synthesized by elec. arc synthesis (1.3-1.6 nm). We also demonstrate that refined species are readily obtained from both the metallic and semiconducting subpopulations of SWCNTs and that this methodol. is effective for multiple SWCNT raw materials. Using these data, we report an empirical function for the necessary surfactant concns. in the ATPE method for sepg. different SWCNTs into either the lower or upper phase as a function of SWCNT diam. This empirical correlation enables predictive sepn. design and identifies a subset of SWCNTs that behave unusually as compared to other species. These results not only dramatically increase the range of SWCNT diams. to which species selective sepn. can be achieved but also demonstrate that aq. two-phase sepns. can be designed across exptl. accessible ranges of surfactant concns. to controllably sep. SWCNT populations of very small (∼0.62 nm) to very large diams. (>1.7 nm). Together, the results reported here indicate that total sepn. of all SWCNT species is likely feasible by the ATPE method, esp. given future development of multistage automated extn. techniques.
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    48. 48
      Hirano, A.; Tanaka, T.; Urabe, Y.; Kataura, H. PH-and solute-dependent adsorption of single-wall carbon nanotubes onto hydrogels: Mechanistic insights into the metal/semiconductor separation. ACS Nano 2013, 7, 10285– 10295,  DOI: 10.1021/nn4046776
      48
      pH- and Solute-Dependent Adsorption of Single-Wall Carbon Nanotubes onto Hydrogels: Mechanistic Insights into the Metal/Semiconductor Separation
      Hirano, Atsushi; Tanaka, Takeshi; Urabe, Yasuko; Kataura, Hiromichi
      ACS Nano (2013), 7 (11), 10285-10295CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      The gel sepn. of single-wall carbon nanotubes (SWCNTs) suspended in sodium dodecyl sulfate (SDS) is expected to be one of the most successful methods of large-scale and high-purity sepn. Understanding the mechanism of the gel sepn. helps improve the quality and quantity of sepn. and reveals the colloidal behaviors of SWCNTs, which reflects their band structures. In this study, we characterize the pH- and solute-dependent adsorption of SWCNTs onto agarose and Sephacryl hydrogels and provide a mechanistic model of the metal/semiconductor sepn. The adsorbability of SWCNTs is substantially reduced under acidic pH conditions. Importantly, the pH dependence differs between metallic and semiconducting species; therefore, the adsorbability is related to the band-structure-dependent oxidn. of the SWCNTs. Oxidn. confers pos. charges on SWCNTs, and these charges enhance the electrostatic interactions of the SWCNTs with SDS, thereby leading to the condensation of SDS on the SWCNTs. This increase in SDS d. reduces the interactions between the SWCNTs and hydrogels. Under highly basic conditions, such as pH ∼12.5, or in the presence of salts, the adsorption is dissociative because of the condensation of SDS on the SWCNTs through electrostatic screening by counterions. Desorption of the SWCNTs from the hydrogels due to the addn. of urea implies a hydrophobic interface between SDS-dispersed SWCNTs and the hydrogels. These results suggest that the metal/semiconductor sepn. can be explained by the alteration of the interaction between SDS-dispersed SWCNTs and the hydrogels through changes in the conformation of SDS on the SWCNTs depending on the SWCNTs' band structures.
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    49. 49
      Flavel, B. S.; Moore, K. E.; Pfohl, M.; Kappes, M. M.; Hennrich, F. Separation of single-walled carbon nanotubes with a gel permeation chromatography system. ACS Nano 2014, 8, 1817– 1826,  DOI: 10.1021/nn4062116
      49
      Separation of Single-Walled Carbon Nanotubes with a Gel Permeation Chromatography System
      Flavel, Benjamin S.; Moore, Katherine E.; Pfohl, Moritz; Kappes, Manfred M.; Hennrich, Frank
      ACS Nano (2014), 8 (2), 1817-1826CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      A gel permeation chromatog. system is used to sep. aq. sodium dodecyl sulfate suspensions of single-walled carbon nanotubes (SWCNTs). This automated procedure requires no precentrifugation, is scalable, and is found to yield monochiral SWCNT fractions of semiconducting SWCNTs with a purity of 61-95%. Unsorted and resulting monochiral fractions are characterized using optical absorption and photoluminescence spectroscopy.
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    50. 50
      Leeuw, T. K.; Tsyboulski, D. A.; Nikolaev, P. N.; Bachilo, S. M.; Arepalli, S.; Weisman, R. B. Strain Measurements on Individual Single-Walled Carbon Nanotubes in a Polymer Host: Structure-Dependent Spectral Shifts and Load Transfer. Nano Lett. 2008, 8, 826– 831,  DOI: 10.1021/nl072861c
      50
      Strain Measurements on Individual Single-Walled Carbon Nanotubes in a Polymer Host: Structure-Dependent Spectral Shifts and Load Transfer
      Leeuw, Tonya K.; Tsyboulski, Dmitri A.; Nikolaev, Pavel N.; Bachilo, Sergei M.; Arepalli, Sivaram; Weisman, R. Bruce
      Nano Letters (2008), 8 (3), 826-831CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      The fluorescence of individual semiconducting single-walled C nanotubes embedded in polymer films was measured during the application of controlled stretching and compressive strains. Nanotube band gaps shift in systematic patterns that depend on the (n,m) structural type and are in agreement with the predictions of theor. models. Loss of nanotube-host adhesion was revealed by abrupt irregularities in plots of spectral shift vs. strain.
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    51. 51
      Huang, M.; Wu, Y.; Chandra, B.; Yan, H.; Shan, Y.; Heinz, T. F.; Hone, J. Direct measurement of strain-induced changes in the band structure of carbon nanotubes. Phys. Rev. Lett. 2008, 100, 136803,  DOI: 10.1103/PhysRevLett.100.136803
      51
      Direct Measurement of Strain-Induced Changes in the Band Structure of Carbon Nanotubes
      Huang, Mingyuan; Wu, Yang; Chandra, Bhupesh; Yan, Hugen; Shan, Yuyao; Heinz, Tony F.; Hone, James
      Physical Review Letters (2008), 100 (13), 136803/1-136803/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      The effect of uniaxial strain on the optical transition energies of single-walled C nanotubes with known chiral indexes was measured by Rayleigh scattering spectroscopy. Existing theory accurately predicts the trends in the measured strain-induced shifts, but overestimates their magnitude. Modification of the anal. to account for internal sublattice relaxation results in quant. agreement with expt.
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    52. 52
      Valavala, P. K.; Banyai, D.; Seel, M.; Pati, R. Self-consistent calculations of strain-induced band gap changes in semiconducting (n,0) carbon nanotubes. Physical Review B - Condensed Matter and Materials Physics 2008, 78, 235430,  DOI: 10.1103/PhysRevB.78.235430
      52
      Self-consistent calculations of strain-induced band gap changes in semiconducting (n,0) carbon nanotubes
      Valavala, Pavan K.; Banyai, Douglas; Seel, Max; Pati, Ranjit
      Physical Review B: Condensed Matter and Materials Physics (2008), 78 (23), 235430/1-235430/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      First-principles d.-functional calcns. of the electronic structure, energy band gaps (Eg), and strain-induced band gap changes in moderate-gap single-walled (n,0) carbon nanotubes (SWNTs) are presented. It is confirmed that (n,0) SWNTs fall into two classes depending upon n mod 3=1 or 2. Eg is always lower for "mod 1" than for "mod 2" SWNTs of similar diam. For n < 10, strong curvature effects dominate Eg; from n = 10 to 17, the Eg oscillations, amplified due to σ-π mixing, decrease and can be explained very well with a tight-binding model which includes trigonal warping. Under strain, the two families of semiconducting SWNTs are distinguished by equal and opposite energy shifts for these gaps. For (10,0) and (20,0) tubes, the potential surface and band gap changes are explored up to approx. ±6% strain or compression. For each strain value, full internal geometry relaxation is allowed. The calcd. band gap changes are ±(115 ± 10) meV per 1% strain, pos. for the mod 1 and neg. for the mod 2 family, about 10% larger than the tight-binding result of ±97 meV and twice as large as the shift predicted from a tight-binding model that includes internal sublattice relaxation.
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    53. 53
      Streit, J.; Snyder, C. R.; Campo, J.; Zheng, M.; Simpson, J. R.; Hight Walker, A. R.; Fagan, J. A. Alkane Encapsulation Induces Strain in Small-Diameter Single-Wall Carbon Nanotubes. J. Phys. Chem. C 2018, 122, 11577– 11585,  DOI: 10.1021/acs.jpcc.8b03166
      53
      Alkane Encapsulation Induces Strain in Small-Diameter Single-Wall Carbon Nanotubes
      Streit, Jason; Snyder, Chad R.; Campo, Jochen; Zheng, Ming; Simpson, Jeffrey R.; Hight Walker, Angela R.; Fagan, Jeffrey A.
      Journal of Physical Chemistry C (2018), 122 (21), 11577-11585CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      Encapsulation of linear alkane mols. in the endohedral vols. of small-diam. single-wall carbon nanotubes (SWCNTs) is shown to induce diam.-dependent strain on the hexagonal lattice of carbon atoms composing the tubular structure. For the smallest diam. nanotubes, such as the (6,5), (9,1), (8,3), and (10,0), encapsulation leads to expansive radial strain. This effect is demonstrated through precision measurements of induced shifts in the energy of the intrinsic optical transitions of single-chirality nanotube populations. The effect on the optical transitions from strain is found to exceed that of the effective dielec. medium change when comparing the same SWCNT population filled with an alkane vs. those filled with water. This differs from encapsulation of alkanes into larger-diam. nanotubes, for which dielec. effects dominate because of the relative sizes of the guest mols. and the SWCNT cavity. For the SWCNT species examd. in this work, the interior cavity diams. are smaller than the smallest unstrained cross-section of an alkane mol. These results imply that SWCNT species-dependent strain is likely to be encountered when encapsulating any mol. into a SWCNT, with particular complexity to be expected for filling by mols. close to the sieving size of the endohedral cavity.
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    54. 54
      Kashtiban, R. J.; Burdanova, M. G.; Vasylenko, A.; Wynn, J.; Medeiros, P. V.; Ramasse, Q.; Morris, A. J.; Quigley, D.; Lloyd-Hughes, J.; Sloan, J. Linear and Helical Cesium Iodide Atomic Chains in Ultranarrow Single-Walled Carbon Nanotubes: Impact on Optical Properties. ACS Nano 2021, 15, 13389– 13398,  DOI: 10.1021/acsnano.1c03705
      54
      Linear and Helical Cesium Iodide Atomic Chains in Ultranarrow Single-Walled Carbon Nanotubes: Impact on Optical Properties
      Kashtiban, Reza J.; Burdanova, Maria G.; Vasylenko, Andrij; Wynn, Jamie; Medeiros, Paulo V. C.; Ramasse, Quentin; Morris, Andrew J.; Quigley, David; Lloyd-Hughes, James; Sloan, Jeremy
      ACS Nano (2021), 15 (8), 13389-13398CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      One-dimensional (1D) at. chains of CsI were previously reported in double-walled carbon nanotubes with ~ 0.8 nm inner diam. Here, we demonstrate that, while 1D CsI chains form within narrow ~ 0.73 nm diam. single-walled carbon nanotubes (SWCNTs), wider SWCNT tubules (~ 0.8-1.1 nm) promote the formation of helical chains of CsI 2 x 1 atoms in cross-section. These CsI helixes create complementary oval distortions in encapsulating SWCNTs with highly strained helixes formed from strained Cs2I2 parallelogram units in narrow tubes to lower strain Cs2I2 units in wider tubes. The obsd. structural changes and charge distribution were analyzed by d.-functional theory and Bader anal. CsI chains also produce conformation-selective changes to the electronic structure and optical properties of the encapsulating tubules. The obsd. defects are an interesting variation from defects commonly obsd. in alkali halides as these are normally assocd. with the Schottky and Frenkel type. The energetics of CsI 2 x 1 helix formation in SWCNTs suggests how these could be controllably formed.
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    55. 55
      Raravikar, N. R.; Keblinski, P.; Rao, A. M.; Dresselhaus, M. S.; Schadler, L. S.; Ajayan, P. M. Temperature dependence of radial breathing mode Raman frequency of single-walled carbon nanotubes. Phys. Rev. B 2002, 66, 235424,  DOI: 10.1103/PhysRevB.66.235424
      55
      Temperature dependence of radial breathing mode Raman frequency of single-walled carbon nanotubes
      Raravikar, Nachiket R.; Keblinski, Pawel; Rao, Apparao M.; Dresselhaus, Mildred S.; Schadler, Linda S.; Ajayan, Pulickel M.
      Physical Review B: Condensed Matter and Materials Physics (2002), 66 (23), 235424/1-235424/9CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      Recent high-temp. studies of Raman-active modes in single-walled carbon nanotube (SWNT) bundles report a softening of the radial and tangential band frequencies with increasing sample temp. A few speculations have been proposed in the past to explain the origin of these frequency downshifts. In the present study, based on exptl. data and the results of mol. dynamics simulations, we est. the contributions from 3 factors that may be responsible for the obsd. temp. dependence of the radial breathing mode frequency [ωRBM(T)]. These factors include thermal expansion of individual SWNTs in the radial direction, softening of the C-C (intratubular) bonds, and softening of the van der Waals intertubular interactions in SWNT bundles. Based on our anal., we find that the first factor plays a minor role due to the very small value of the radial thermal expansion coeff. of SWNTs. On the contrary, the temp.-induced softening of the intra- and intertubular bonds contributes significantly to the temp.-dependent shift of ωRBM(T). For nanotubes with diams. (d)≥1.34 nm, the contribution due to the radial thermal expansion is ≤4% over the temp. range used in this study. Interestingly, this contribution increases to ≥10% in the case of nanotubes having d≤0.89 nm due to the relatively larger curvature of these nanotubes. The contributions from the softening of the intra- and intertubular bonds are approx. equal. These 2 factors together contribute a total of about ∼95% and 90%, resp., for SWNTs having d≥1.34 nm and ≤0.89 nm.
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    56. 56
      May, P.; Telg, H.; Zhong, G.; Robertson, J.; Thomsen, C.; Maultzsch, J. Observation of excitonic effects in metallic single-walled carbon nanotubes. Phys. Rev. B 2010, 82, 195412,  DOI: 10.1103/PhysRevB.82.195412
      56
      Observation of excitonic effects in metallic single-walled carbon nanotubes
      May, Patrick; Telg, Hagen; Zhong, Guofang; Robertson, John; Thomsen, Christian; Maultzsch, Janina
      Physical Review B: Condensed Matter and Materials Physics (2010), 82 (19), 195412/1-195412/6CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      Excitonic effects of metallic single-walled carbon nanotubes are measured with temp.-dependent resonant Raman spectroscopy. By changing the temp. in the range of 300-870 K, we observe variations in the optical transition energy Eii as well as in the max. Raman intensity. We find both dependences to be different for semiconducting and metallic single-walled carbon nanotubes. We suggest an interpretation in terms of excitons dissocd. into free electron-hole pairs at temps. related to the exciton binding energy. We furthermore discuss how the oscillator strength is influenced by temp.
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    57. 57
      Brar, V. W.; Samsonidze, G. G.; Dresselhaus, M. S.; Dresselhaus, G.; Saito, R.; Swan, A. K.; Ünlü, M. S.; Goldberg, B. B.; Souza Filho, A. G.; Jorio, A. Second-order harmonic and combination modes in graphite, single-wall carbon nanotube bundles, and isolated single-wall carbon nanotubes. Phys. Rev. B 2002, 66, 155418,  DOI: 10.1103/PhysRevB.66.155418
      57
      Second-order harmonic and combination modes in graphite, single-wall carbon nanotube bundles, and isolated single-wall carbon nanotubes
      Brar, V. W.; Samsonidze, Ge. G.; Dresselhaus, M. S.; Dresselhaus, G.; Saito, R.; Swan, A. K.; Unlu, M. S.; Goldberg, B. B.; Souza Filho, A. G.; Jorio, A.
      Physical Review B: Condensed Matter and Materials Physics (2002), 66 (15), 155418/1-155418/10CODEN: PRBMDO; ISSN:0163-1829. (American Physical Society)
      The authors report a study of 2nd-order combination and overtone modes in highly ordered pyrolytic graphite (HOPG), in single-wall C nanotube (SWNT) bundles and in isolated SWNTs. The authors found both dispersive and nondispersive Raman bands in the range 1650-2100 cm-1, and the appearance and frequency vs. laser energy Elaser behavior of these features are in agreement with predictions from double-resonance Raman theory. In the case of SWNTs, these 2nd-order bands depend on the 1-dimensional structure of SWNTs, and at the single nanotube level, the spectra vary from tube to tube, depending on tube diam. and chirality and on the energy of the van Hove singularity relative to Elaser.
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    58. 58
      Rao, R.; Reppert, J.; Podila, R.; Zhang, X.; Rao, A. M.; Talapatra, S.; Maruyama, B. Double resonance Raman study of disorder in CVD-grown single-walled carbon nanotubes. Carbon 2011, 49, 1318– 1325,  DOI: 10.1016/j.carbon.2010.11.052
      58
      Double resonance Raman study of disorder in CVD-grown single-walled carbon nanotubes
      Rao, Rahul; Reppert, Jason; Podila, Ramakrishna; Zhang, Xianfeng; Rao, Apparao M.; Talapatra, Saikat; Maruyama, Benji
      Carbon (2011), 49 (4), 1318-1325CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Single-walled carbon nanotubes (SWCNTs) with varying degrees of disorder were investigated using multiple-excitation Raman spectroscopy. The lattice disorder was imparted into the nanotubes by the addn. of varying amts. of sulfur to the iron catalyst in a thermal chem. vapor deposition process. Changes in the intensities of peaks occurring due to a double resonance Raman process were studied. The intensity of the disorder-induced D band increased with a decrease in the sulfur content. Upon post-synthesis heat treatment, the double resonance process got quenched due to defect healing. The second order G' band and iTOLA bands exhibited a two-peak structure, of which one of the peaks is relatively more sensitive to defects and decreased in intensity with heat treatment.
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    59. 59
      Dukovic, G.; White, B. E.; Zhou, Z.; Wang, F.; Jockusch, S.; Steigerwald, M. L.; Heinz, T. F.; Friesner, R. A.; Turro, N. J.; Brus, L. E. Reversible surface oxidation and efficient luminescence quenching in semiconductor single-wall carbon nanotubes. J. Am. Chem. Soc. 2004, 126, 15269– 15276,  DOI: 10.1021/ja046526r
      59
      Reversible Surface Oxidation and Efficient Luminescence Quenching in Semiconductor Single-Wall Carbon Nanotubes
      Dukovic, Gordana; White, Brian E.; Zhou, Zhiyong; Wang, Feng; Jockusch, Steffen; Steigerwald, Michael L.; Heinz, Tony F.; Friesner, Richard A.; Turro, Nicholas J.; Brus, Louis E.
      Journal of the American Chemical Society (2004), 126 (46), 15269-15276CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)
      We have investigated reversible single-wall carbon nanotube (SWNT) oxidn. by quant. anal. of the oxide-induced absorption bleaching and luminescence quenching at low pH. These data, in combination with DFT structure calcns., suggest that the nanotube oxide is a 1,4-endoperoxide. At low pH, the endoperoxide protonates to create a hydroperoxide carbocation, introducing a hole in the SWNT valence band. Nanotube luminescence is extremely sensitive to quenching by hole-doping, while the absorption is relatively robust.
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    60. 60
      Dowgiallo, A. M.; Mistry, K. S.; Johnson, J. C.; Blackburn, J. L. Ultrafast spectroscopic signature of charge transfer between single-walled carbon nanotubes and C60. ACS Nano 2014, 8, 8573– 8581,  DOI: 10.1021/nn503271k
      60
      Ultrafast Spectroscopic Signature of Charge Transfer between Single-Walled Carbon Nanotubes and C60
      Dowgiallo, Anne-Marie; Mistry, Kevin S.; Johnson, Justin C.; Blackburn, Jeffrey L.
      ACS Nano (2014), 8 (8), 8573-8581CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)
      The time scales for interfacial charge sepn. and recombination play crucial roles in detg. efficiencies of excitonic photovoltaics. Near-IR photons are harvested efficiently by semiconducting single-walled carbon nanotubes (SWCNTs) paired with appropriate electron acceptors, such as fullerenes (e.g., C60). However, little is known about crucial photochem. events that occur on femtosecond to nanosecond time scales at such heterojunctions. Here, we present transient absorbance measurements that utilize a distinct spectroscopic signature of charges within SWCNTs, the absorbance of a trion quasiparticle, to measure both the ultrafast photoinduced electron transfer time (τpet) and yield (.vphi.pet) in photoexcited SWCNT-C60 bilayer films. The rise time of the trion-induced absorbance enables the detn. of the photoinduced electron transfer (PET) time of τpet ≤ 120 fs, while an exptl. detd. trion absorbance cross section reveals the yield of charge transfer (.vphi.pet ≈ 38 ± 3%). The extremely fast electron transfer times obsd. here are on par with some of the best donor:acceptor pairs in excitonic photovoltaics and underscore the potential for efficient energy harvesting in SWCNT-based devices.
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    61. 61
      Kharlamova, M. V.; Sauer, M.; Saito, T.; Sato, Y.; Suenaga, K.; Pichler, T.; Shiozawa, H. Doping of single-walled carbon nanotubes controlled via chemical transformation of encapsulated nickelocene. Nanoscale 2015, 7, 1383– 1391,  DOI: 10.1039/C4NR05586A
      61
      Doping of single-walled carbon nanotubes controlled via chemical transformation of encapsulated nickelocene
      Kharlamova, Marianna V.; Sauer, Markus; Saito, Takeshi; Sato, Yuta; Suenaga, Kazu; Pichler, Thomas; Shiozawa, Hidetsugu
      Nanoscale (2015), 7 (4), 1383-1391CODEN: NANOHL; ISSN:2040-3372. (Royal Society of Chemistry)
      Controlled doping of carbon nanotubes is elemental for their electronic applications. Here we report an approach to tune the polarity and degree of doping of single-walled carbon nanotubes via filling with nickelocene followed by encapsulated reactions. Using Raman, photoemission spectroscopy and transmission electron microscopy, we show that nickelocene mols. transform into nickel carbides, nickel and inner carbon nanotubes with reaction temps. as low as 250 °C. The doping efficiency is detd. for each chem. component. Synchronous charge transfer among the mol. components allows bipolar doping of the carbon nanotubes to be achieved in a broad range of ±0.0012 e- per carbon.
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    62. 62
      Styers-Barnett, D. J.; Ellison, S. P.; Mehl, B. P.; Westlake, B. C.; House, R. L.; Park, C.; Wise, K. E.; Papanikolas, J. M. Exciton dynamics and biexciton formation in single-walled carbon nanotubes studied with femtosecond transient absorption spectroscopy. J. Phys. Chem. C 2008, 112, 4507– 4516,  DOI: 10.1021/jp7099256
      62
      Exciton Dynamics and Biexciton Formation in Single-Walled Carbon Nanotubes Studied with Femtosecond Transient Absorption Spectroscopy
      Styers-Barnett, David J.; Ellison, Stephen P.; Mehl, Brian P.; Westlake, Brittany C.; House, Ralph L.; Park, Cheol; Wise, Kristopher E.; Papanikolas, John M.
      Journal of Physical Chemistry C (2008), 112 (12), 4507-4516CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)
      The authors used femtosecond transient absorption (TA) spectroscopy to examine the excited state dynamics of single-walled C nanotube (SWNT) bundles embedded in polymer matrixes. The SWNTs were excited by a femtosecond pump pulse centered at either 1800, 900, or 550 nm and probed using a white-light continuum extending from 400 to 750 nm. The authors obsd. a structured TA spectrum consisting of narrow induced transmission (IT) and induced absorption (IA) bands. The TA spectrum, which is independent of excitation wavelength, appeared on a time scale shorter than instrument response (200 fs) and persisted for up to 100 ps. TA spectra obtained at pump-probe delay times provided a window through which to monitor the exciton dynamics. The authors obsd. 3 distinct spectral signatures in the time-dependent data: (1) the decay of a broad photobleach, (2) the biphasic decay of narrow IT and IA features, and (3) a dynamical spectral shift of IA bands. These processes were attributed to plasmon relaxation, electron-hole recombination, and lattice relaxation assocd. with exciton self-trapping, resp. Anal. of the transient spectrum suggested that it arose from a nonlinear optical response of the SWNT, where excitons produced by the pump pulse modified the transition frequencies of subsequent carrier excitations. The result was IT bands (bleaches) at the ground state absorption frequencies, and assocd. with each were a corresponding red-shifted absorption band. These induced absorptions were attributed to the formation of biexcitons, 4-particle excitations that are produced through the sequential excitation of 2 closely spaced electron-hole pairs.
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    63. 63
      Yuma, B.; Berciaud, S.; Besbas, J.; Shaver, J.; Santos, S.; Ghosh, S.; Weisman, R. B.; Cognet, L.; Gallart, M.; Ziegler, M.; Hönerlage, B.; Lounis, B.; Gilliot, P. Biexciton, single carrier, and trion generation dynamics in single-walled carbon nanotubes. Physical Review B - Condensed Matter and Materials Physics 2013, 87, 205412,  DOI: 10.1103/PhysRevB.87.205412
      63
      Biexciton, single carrier, and trion generation dynamics in single-walled carbon nanotubes
      Yuma, B.; Berciaud, S.; Besbas, J.; Shaver, J.; Santos, S.; Ghosh, S.; Weisman, R. B.; Cognet, L.; Gallart, M.; Ziegler, M.; Honerlage, B.; Lounis, B.; Gilliot, P.
      Physical Review B: Condensed Matter and Materials Physics (2013), 87 (20), 205412/1-205412/7CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      We present a study of free carrier photogeneration and multicarrier bound states, such as biexcitons and trions (charged excitons), in semiconducting single-walled carbon nanotubes. Pump-and-probe measurements performed with fs pulses reveal the effects of strong Coulomb interactions between carriers on their dynamics. Biexciton formation by optical transition from exciton population results in an induced absorption line (binding energy 130 meV). Exciton-exciton annihilation process is shown to evolve at high densities towards an Auger process that can expel carriers from nanotubes. The remaining carriers give rise to an induced absorption due to trion formation (binding energy 190 meV). These features show the dynamics of exciton and free carriers populations.
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    64. 64
      Miyauchi, Y.; Saito, R.; Sato, K.; Ohno, Y.; Iwasaki, S.; Mizutani, T.; Jiang, J.; Maruyama, S. Dependence of exciton transition energy of single-walled carbon nanotubes on surrounding dielectric materials. Chem. Phys. Lett. 2007, 442, 394– 399,  DOI: 10.1016/j.cplett.2007.06.018
      64
      Dependence of exciton transition energy of single-walled carbon nanotubes on surrounding dielectric materials
      Miyauchi, Y.; Saito, R.; Sato, K.; Ohno, Y.; Iwasaki, S.; Mizutani, T.; Jiang, J.; Maruyama, S.
      Chemical Physics Letters (2007), 442 (4-6), 394-399CODEN: CHPLBC; ISSN:0009-2614. (Elsevier B.V.)
      The authors theor. study the environmental effect for optical transition energies of single-walled C nanotubes (SWNTs), by calcg. the exciton transition energies of SWNTs. The static dielec. consts. used in the exciton calcn. can be expressed as a function of the dielec. consts. of the surrounding material and that of the SWNT, in which the static and dynamic dielec. consts. of the SWNT represent the screening effect of core electrons and the valence π electrons, resp. The calcd. results reproduce the environmental effect of the exptl. transition energies for various surrounding materials and for various diams. of SWNTs.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXnsVSrsL8%253D&md5=4626ced1894b3ca3acdd118e73b8fd4f
    65. 65
      Allam, J.; Sajjad, M. T.; Sutton, R.; Litvinenko, K.; Wang, Z.; Siddique, S.; Yang, Q. H.; Loh, W. H.; Brown, T. Measurement of a reaction-diffusion crossover in exciton-exciton recombination inside carbon nanotubes using femtosecond optical absorption. Phys. Rev. Lett. 2013, 111, 197401,  DOI: 10.1103/PhysRevLett.111.197401
      65
      Measurement of a reaction-diffusion crossover in exciton-exciton recombination inside carbon nanotubes using femtosecond optical absorption
      Allam, J.; Sajjad, M. T.; Sutton, R.; Litvinenko, K.; Wang, Z.; Siddique, S.; Yang, Q.-H.; Loh, W. H.; Brown, T.
      Physical Review Letters (2013), 111 (19), 197401/1-197401/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Exciton-exciton recombination in isolated semiconducting single-walled carbon nanotubes was studied using femtosecond transient absorption. Under sufficient excitation to sat. the optical absorption, we obsd. an abrupt transition between reaction- and diffusion-limited kinetics, arising from reactions between incoherent localized excitons with a finite probability of ∼0.2 per encounter. This represents the first exptl. observation of a crossover between classical and crit. kinetics in a 1D coalescing random walk, which is a paradigm for the study of nonequil. systems.
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    66. 66
      Soavi, G.; Dal Conte, S.; Manzoni, C.; Viola, D.; Narita, A.; Hu, Y.; Feng, X.; Hohenester, U.; Molinari, E.; Prezzi, D.; Müllen, K.; Cerullo, G. Exciton-exciton annihilation and biexciton stimulated emission in graphene nanoribbons. Nat. Commun. 2016, 7, 11010,  DOI: 10.1038/ncomms11010
      66
      Exciton-exciton annihilation and biexciton stimulated emission in graphene nanoribbons
      Soavi, Giancarlo; Dal Conte, Stefano; Manzoni, Cristian; Viola, Daniele; Narita, Akimitsu; Hu, Yunbin; Feng, Xinliang; Hohenester, Ulrich; Molinari, Elisa; Prezzi, Deborah; Mullen, Klaus; Cerullo, Giulio
      Nature Communications (2016), 7 (), 11010CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)
      Graphene nanoribbons display extraordinary optical properties due to one-dimensional quantum-confinement, such as width-dependent bandgap and strong electron-hole interactions, responsible for the formation of excitons with extremely high binding energies. Here we use femtosecond transient absorption spectroscopy to explore the ultrafast optical properties of ultranarrow, structurally well-defined graphene nanoribbons as a function of the excitation fluence, and the impact of enhanced Coulomb interaction on their excited states dynamics. We show that in the high-excitation regime biexcitons are formed by nonlinear exciton-exciton annihilation, and that they radiatively recombine via stimulated emission. We obtain a biexciton binding energy of ≈250 meV, in very good agreement with theor. results from quantum Monte Carlo simulations. These observations pave the way for the application of graphene nanoribbons in photonics and optoelectronics.
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    67. 67
      Shao, D.; Yotprayoonsak, P.; Saunajoki, V.; Ahlskog, M.; Virtanen, J.; Kangas, V.; Volodin, A.; Haesendonck, C.; Burdanova, M.; Mosley, C.; Lloyd-Hughes, J. Conduction properties of thin films from a water soluble carbon nanotube/hemicellulose complex. Nanotechnology 2018, 29, 145203,  DOI: 10.1088/1361-6528/aaabd1
      67
      Conduction properties of thin films from a water soluble carbon nanotube/ hemicellulose complex
      Shao, Dongkai; Yotprayoonsak, Peerapong; Saunajoki, Ville; Ahlskog, Markus; Virtanen, Jorma; Kangas, Veijo; Volodin, Alexander; Haesendonck, Chris Van; Burdanova, Maria; Mosley, Connor D. W.; Lloyd-Hughes, James
      Nanotechnology (2018), 29 (14), 145203/1-145203/9CODEN: NNOTER; ISSN:1361-6528. (IOP Publishing Ltd.)
      We have examd. the conductive properties of carbon nanotube based thin films, which were prepd. via dispersion in water by non-covalent functionalization of the nanotubes with xylan, a type of hemicellulose. Measurements of low temp. cond., Kelvin probe force microscopy, and high frequency (THz) cond. elucidated the intra-tube and inter-tube charge transport processes in this material. The measurements show excellent conductive properties of the as prepd. thin films, with bulk cond. up to 2000 S cm-1. The transport results demonstrate that the hemicellulose does not seriously interfere with the inter-tube conductance.
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    68. 68
      Schneck, J. R.; Walsh, A. G.; Green, A. A.; Hersam, M. C.; Ziegler, L. D.; Swan, A. K. Electron correlation effects on the femtosecond dephasing dynamics of e 22 excitons in (6,5) carbon nanotubes. J. Phys. Chem. A 2011, 115, 3917– 3923,  DOI: 10.1021/jp108345t
      68
      Electron Correlation Effects on the Femtosecond Dephasing Dynamics of E22 Excitons in (6,5) Carbon Nanotubes
      Schneck, J. R.; Walsh, A. G.; Green, A. A.; Hersam, M. C.; Ziegler, L. D.; Swan, A. K.
      Journal of Physical Chemistry A (2011), 115 (16), 3917-3923CODEN: JPCAFH; ISSN:1089-5639. (American Chemical Society)
      Highly nonlinear pump fluence dependence was obsd. in the ultrafast 1-color pump-probe responses excited by 38 fs pulses resonant with the E22 transition in a room-temp. soln. of (6,5) C nanotubes. The differential probe transmission (ΔT/T) at the peak of the pump-probe response (τ = 20 fs) was measured for pump fluences from ∼1013 to 1017 photons/pulse cm2. The onset of satn. is obsd. at ∼2 × 1015 photons/pulse cm2 (∼8 × 105 excitons/cm). At pump fluences >4 × 1016 photons/pulse cm2 (∼1.6 × 106 excitons/cm), ΔT/T decreases as the pump fluence increases. Analogous signal satn. behavior was obsd. for all measured probe delays. Despite the high exciton d. at satn., no change in the E22 population decay rate was obsd. at short times (<300 fs). The pump probe signal was modeled by a 3rd-order perturbation theory treatment that includes the effects of inhomogeneous broadening. The obsd. ΔT/T signal is well-fit by a pump-fluence-dependent dephasing rate linearly dependent on the no. of excitons created by the pump pulse. Therefore, the obsd. nonlinear pump intensity dependence is attributed to the effects of quasi-elastic exciton-exciton interactions on the dephasing rates of single C nanotubes. The low fluence total dephasing time is 36 fs, corresponding to a homogeneous width of 36 meV (290 cm-1), and the derived E22 inhomogeneous width is 68 meV (545 cm-1). These results are contrasted with photon-echo-derived parameters for the E11 transition.
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