Random networks of single-walled carbon nanotubes show promise for use in the field of flexible electronics. Nanotube networks have been difficult to utilize because of the mixture of electronic types synthesized when grown. A variety of separation techniques have been developed, but few can readily be scaled up. Despite this issue, when metallic percolation pathways can be separated out or etched away, these networks serve as high-quality thin-film transistors with impressive device characteristics. A new article in this issue illustrates this point and the promise of these materials. With more work, these devices can be implemented in transparent displays in the next generation of hand-held electronics.

Hexagonal boron nitride (h-BN) is a layered material with a graphite-like structure in which planar networks of BN hexagons are regularly stacked. As the structural analogue of a carbon nanotube (CNT), a BN nanotube (BNNT) was first predicted in 1994; since then, it has become one of the most intriguing non-carbon nanotubes. Compared with metallic or semiconducting CNTs, a BNNT is an electrical insulator with a band gap of ca. 5 eV, basically independent of tube geometry. In addition, BNNTs possess a high chemical stability, excellent mechanical properties, and high thermal conductivity. The same advantages are likely applicable to a graphene analogue—a monatomic layer of a hexagonal BN. Such unique properties make BN nanotubes and nanosheets a promising nanomaterial in a variety of potential fields such as optoelectronic nanodevices, functional composites, hydrogen accumulators, electrically insulating substrates perfectly matching the CNT, and graphene lattices. This review gives an introduction to the rich BN nanotube/nanosheet field, including the latest achievements in the synthesis, structural analyses, and property evaluations, and presents the purpose and significance of this direction in the light of the general nanotube/nanosheet developments.

Optically transparent and mechanically flexible thin-film transistors have recently attracted attention for next generation transparent display technologies. Driving and switching transistors for transparent displays have challenging requirements such as high optical transparency, large-scale integration, suitable drive current (Ion) in the microampere range, high on/off current ratio (Ion/Ioff), high field-effect mobility, and uniform threshold voltage (Vth). In this study, we demonstrate fully transparent high-performance and high-yield thin-film transistors based on random growth of a single-walled carbon nanotube (SWNT) network that are easy to fabricate. High-performance SWNT-TFTs exhibit optical transmission of 80% in visible wavelength, Ion/Ioff higher than 103, and a high yield with reproducible electrical characteristics.

Zero- and one-dimensional metal nanocrystals were successfully fabricated with accurate control in size, shape, and position on semiconductor surfaces by using a novel in situ fabrication method of the nanocrystal with a biasing tungsten tip in transmission electron microscopy. The dominant mechanism of nanocrystal formation was identified mainly as local Joule heating-assisted electromigration through the direct observation of formation and growth processes of the nanocrystal. This method was applied to extracting metal atoms with an exceedingly faster growth rate (∼105 atoms/s) from a metal-oxide thin film to form a metal nanocrystal with any desired size and position. By real-time observation of the microstructure and concurrent electrical measurements, it was found that the nanostructure formation can be completely controlled into various shapes such as zero-dimensional nanodots and one-dimensional nanowires/nanorods.

Liver fibrosis or cirrhosis is one of the representative liver diseases with a high morbidity and mortality worldwide. Over the past decades, many kinds of antifibrotic compounds have been investigated in vitro and in vivo for the treatment of liver cirrhosis. In this work, real-time bioimaging of hyaluronic acid (HA) derivatives was carried out using quantum dots (QDots) to assess the possibility of HA derivatives as target-specific drug delivery carriers for the treatment of liver diseases. HA-QDot conjugates with an HA modification degree of about 22 mol % was synthesized by amide bond formation between carboxyl groups of QDots and amine groups of adipic acid dihydrazide modified HA (HA-ADH). According to in vitro cell culture tests, HA-QDot conjugates were taken up more to the cells causing chronic liver diseases such as hepatic stellate cells (HSC-T6) and hepatoma cells (HepG2) than normal hepatocytes (FL83B). After tail-vein injection, HA-QDot conjugates were target-specific, being delivered to the cirrhotic liver with a slow clearance longer than 8 days. Furthermore, immunofluorescence and flow cytometric analyses of dissected liver tissues revealed the target-specific delivery of HA derivatives to liver sinusoidal endothelial cells (LSEC) and HSC. The results were thought to reflect the feasibility of HA derivatives as novel drug delivery carriers for the treatment of various chronic liver diseases including hepatitis, liver cirrhosis, and liver cancer.

In this work, we reported that the quantum dot (QD) nanoparticles could be actively transported in the membrane nanotubes between cardiac myocytes. Single particle imaging and tracking of QDs revealed that most QDs moved in a bidirectional mode along the membrane nanotubes with a mean velocity of 1.23 μm/s. The results suggested that QDs moving in the nanotubes were coordinately motivated by molecular motors. It provides new information for the study of intercellular transportation of nanoparticles.

Porous silicon (PSi) particles have been studied for the effects they elicit in Caco-2 and RAW 264.7 macrophage cells in terms of toxicity, oxidative stress, and inflammatory response. The most suitable particles were then functionalized with a novel 18F label to assess their biodistribution after enteral and parenteral administration in a rat model. The results show that thermally hydrocarbonized porous silicon (THCPSi) nanoparticles did not induce any significant toxicity, oxidative stress, or inflammatory response in Caco-2 and RAW 264.7 macrophage cells. Fluorescently labeled nanoparticles were associated with the cells surface but were not extensively internalized. Biodistribution studies in rats using novel 18F-labeled THCPSi nanoparticles demonstrated that the particles passed intact through the gastrointestinal tract after oral administration and were also not absorbed from a subcutaneous deposit. After intravenous administration, the particles were found mainly in the liver and spleen, indicating rapid removal from the circulation. Overall, these silicon-based nanosystems exhibit excellent in vivo stability, low cytotoxicity, and nonimmunogenic profiles, ideal for oral drug delivery purposes.

A linker-free connected reduced graphene oxide/CdSe nanoparticle (R-GO/CdSe NP) nanocomposite was produced by directly anchoring CdSe NPs onto R-GO. The morphological and structural characterizations evidence that the single-crystal CdSe NPs with the size of a few tens of nanometers can be efficiently decorated on the R-GO. The photoresponse of this nanocomposite is drastically enhanced compared with that of the pure CdSe NPs, the bare R-GO, and the physically mixed R-GO/CdSe NPs, while the photoluminescence of the CdSe NPs in the composite is much quenched, indicating that the photoinduced carriers generated from the CdSe NPs can be transferred to the R-GO effectively and separately. This ability makes the R-GO/CdSe NP nanocomposite a great promise for wide potential applications in optoelectronics.

We have fabricated an L3 optical nanocavity operating at visible wavelengths that is coated with a thin-film of a fluorescent molecular-dye. The cavity was directly fabricated into a pre-etched, free-standing silicon-nitride (SiN) membrane and had a quality factor of Q = 2650. This relatively high Q-factor approaches the theoretical limit that can be expected from an L3 nanocavity using silicon nitride as a dielectric material and is achieved as a result of the solvent-free cavity-fabrication protocol that we have developed. We show that the fluorescence from a red-emitting fluorescent dye coated onto the cavity surface undergoes strong emission intensity enhancement at a series of discrete wavelengths corresponding to the cavity modes. Three dimensional finite difference time domain (FDTD) calculations are used to predict the mode structure of the cavities with excellent agreement demonstrated between theory and experiment.

p-Type surface conductivity is a uniquely important property of hydrogen-terminated diamond surfaces. In this work, we report similar surface-dominated electrical properties in silicon nanowires (SiNWs). Significantly, we demonstrate tunable and reversible transition of p+−p−i−n−n+ conductance in nominally intrinsic SiNWs via changing surface conditions, in sharp contrast to the only p-type conduction observed on diamond surfaces. On the basis of Si band energies and the electrochemical potentials of the ambient (pH value)-determined adsorbed aqueous layer, we propose an electron-transfer-dominated surface doping model, which can satisfactorily explain both diamond and silicon surface conductivity. The totality of our observations suggests that nanomaterials can be described as a core−shell structure due to their large surface-to-volume ratio. Consequently, controlling the surface or shell in the core−shell model represents a universal way to tune the properties of nanostructures, such as via surface-transfer doping, and is crucial for the development of nanostructure-based devices.

The plasmon coupling in the dimers of Au nanorods linked together at their ends with dithiol molecules has been studied. The plasmon coupling in the dimers composed of similarly sized nanorods gives antibonding and bonding plasmon modes. The plasmon wavelengths of the two modes have been found to remain approximately unchanged, with the scattering intensity ratio between the antibonding and bonding modes decaying rapidly as the angle between the nanorods is increased. This plasmon coupling behavior agrees with that obtained from both electrodynamic calculations and modeling on the basis of the dipole−dipole interaction. The electric field in the gap region is largely enhanced for the bonding mode, while that for the antibonding mode is even smaller than the far field, highlighting the importance of selecting appropriate plasmon modes for plasmon-enhanced spectroscopies. An anti-crossing-like behavior in the plasmon coupling energy diagram has further been revealed for linearly end-to-end assembled dimers composed of differently sized nanorods. This result will be useful for plasmonic applications where the plasmon wavelength is required to be controllable but without sacrificing the electric field enhancement.

We study the solubility and dispersibility of as-produced and purified HiPco single-walled carbon nanotubes (SWNTs). Variation in specific operating conditions of the HiPco process are found to lead to significant differences in the respective SWNT solubilities in oleum and surfactant suspensions. The diameter distributions of SWNTs dispersed in surfactant solutions are batch-dependent, as evidenced by luminescence and Raman spectroscopies, but are identical for metallic and semiconducting SWNTs within a batch. We thus find that small diameter SWNTs disperse at higher concentration in aqueous surfactants and dissolve at higher concentration in oleum than do large-diameter SWNTs. These results highlight the importance of controlling SWNT synthesis methods in order to optimize processes dependent on solubility, including macroscopic processing such as fiber spinning, material reinforcement, and films production, as well as for fundamental research in type selective chemistry, optoelectronics, and nanophotonics.

Nanoparticle-based in vivo applications should consider the omnipresence of the phagocytes in the bloodstream and tissue. We have studied the nanoparticle uptake capacities of the most important human primary leukocyte populations using a nanoparticle library encompassing both rod-shaped and spherical gold nanoparticles with diameters between 15 and 50 nm and a variety of surface chemistries. Cetyltrimethylammoniumbromide (CTAB)-stabilized nanoparticles were internalized rapidly within 15 min and in large amounts by macrophages and to a lower extent also by monocytes. Interestingly, we found that the uptake of nanorods by macrophages was more efficient than that of nanospheres. Blocking experiments and electron microscopic studies revealed macropinocytosis as the major uptake mechanism. Grafting of poly(ethylene oxide) (PEO) onto the nanorods was found to significantly delay their internalization for several hours. The long-term uptake of PEO-coated nanoparticles with positively or negatively charged end groups was almost identical. Particle surface chemistry strongly influenced the expression of inflammation-related genes within 1 day. Furthermore, the macrophage phenotype was significantly affected after 7 days of culture with nanorods depending on the surface chemistry. Thus, in vivo application of nanoparticles with certain surface functionalities may lead to inflammation upon particle accumulation. However, our data also suggest that chemical modifications of nanoparticles may be useful for immunomodulation.

The most studied effect of surface-enhanced Raman scattering (SERS) hotspots is the enormous Raman enhancement of the analytes therein. A less known effect, though, is that the formation of hotspots may cause the trapped analytes to change molecular orientation, which in turn leads to pronounced changes in SERS fingerprints. Here, we demonstrate this effect by creating and characterizing hotspots in colloidal solutions. Anisotropically functionalized Au nanorods were synthesized, whereby the sides were specifically encapsulated by polystyrene-block-poly(acrylic acid), leaving the ends unencapsulated and functionalized by a SERS analyte, 4-mercaptobenzoic acid. Upon salt treatment, these nanorods assemble into linear chains, forming hotspots that incorporate the SERS analyte. Enormous SERS enhancement was observed, particularly for some weak/inactive SERS modes that were not present in the original spectrum before the hotspots formation. Detailed spectral analysis showed that the variations of the SERS fingerprint were consistent with the reorientation of analyte molecules from nearly upright to parallel/tilted conformation on the Au surface. We propose that the aggregation of Au nanorods exerts physical stress on the analytes in the hotspots, causing the molecular reorientation. Such a hotspot-induced variation of SERS fingerprints was also observed in several other systems using different analytes.

Sheets of chemically converted graphene (CCG) on the surface of Si/SiO2 substrates exhibit nanoscopic corrugation. This corrugation has been assumed to be caused by a combination of factors including (a) thermal treatments in the device preparation, (b) different oxygen-containing addends on the CCG, and (c) the substrate roughness. In this paper, we study the interplay of these factors in the corrugation behavior of monolayer CCG flakes, prepared by reduction of graphene oxide (GO) synthesized by Hummers method, and CCG nanoribbons, produced by chemical unzipping of carbon nanotubes, followed by the reduction by hydrazine at 95 °C. We have studied the morphology, composition, and electrical properties of the flakes and nanoribbons before and after annealing in Ar/H2 at 300 °C. Our experiments demonstrate that, despite the temperature treatment and the associated removal of the oxygen-containing addends from the basal plane of the CCG, the corrugation pattern of the CCG exhibits almost no change upon annealing. This suggests that the substrate roughness, not the chemical addends nor the thermal cycling, is the predominant determinant in the graphene corrugation. This conclusion is supported by depositing GO flakes on freshly cleaved mica. Such flakes were shown to have extremely low corrugation (rms ∼70 pm), as dictated by the atomically flat surface of mica. Our experimental observations are in accord with the results of our molecular dynamics simulations, which show that interaction with the substrate greatly suppresses the intrinsic corrugation of graphene materials.

Devices incorporating nanoscale materials, particularly carbon nanotubes (CNTs), offer exceptional electrical performance. Absent, however, is an experimentally backed model explaining contact-metal work function, device layout, and environment effects. To fill the void, this report introduces a surface-inversion channel model based on low temperature and electrical measurements of a distinct single-walled semiconducting CNT contacted by Hf, Cr, Ti, and Pd electrodes. Anomalous barrier heights and metal-contact dependent band-to-band tunneling phenomena are utilized to show that, dependent upon contact work function and gate field, transport occurs either directly between the metal and CNT channel or indirectly via injection of carriers from the metal-covered CNT region to the CNT channel. The model is consistent with previously contradictory experimental results, and the methodology is simple enough to apply in other contact-dominant systems.

A phase diagram was constructed for a polystyrene-block-polyisoprene (PS-b-PI, MW = 32 700, fPI = 0.670) in thin films on Si wafer as a function of film thickness over the range of 150−2410 nm (7−107L0 (L0: domain spacing)). The PS-b-PI exhibits a variety of ordered phases from hexagonally perforated lamellar (HPL) via double gyroid (DG) to hexagonally packed cylinder (HEX) before going to the disordered (DIS) phase upon heating. The morphology of the PS-b-PI in thin film was investigated by grazing incidence small-angle X-ray scattering, transmission electron microscopy, and transmission electron microtomography. In thin film, the phase transition temperature is difficult to be determined unequivocally with in situ heating processes since the phase transition is slow and two phases coexist over a wide temperature range. Therefore, in an effort to find an “equilibrium” phase, we determined the long-term stable phase formed after cooling the film from the DIS phase to a target temperature and annealing for 24 h at the temperature. The temperature windows of stable ordered phases are strongly influenced by the film thickness. As the film thickness decreases, the temperature window of layer-like structures such as HPL and HEX becomes wider, whereas that of the DG stable region decreases. For the films thinner than 160 nm (8L0), only the HPL phase was found. In the films exhibiting DG phase, a perforated layer structure at the free surface was found, which gradually converts to the internal DG structure. The relief of interfacial tension by preferential wetting appears to play an important role in controlling the morphology in very thin films.

An electronic nose (e-nose) strategy is described based on SnO2 nanowire arrays whose sensing properties are modified by changing their operating temperatures and by decorating some of the nanowires with metallic nanoparticles. Since the catalytic processes occurring on the metal nanoparticles depend on the identity of the metal, decorating the semiconducting nanowires with various metal nanoparticles is akin to functionalizing them with chemically specific moieties. Other than the synthesis of the nanowires, all other steps in the fabrication of the e-nose sensors were carried out using top-down microfabrication processes, paving the way to a useful strategy for making low cost, nanowire-based e-nose chips. The sensors were tested for their ability to distinguish three reducing gases (H2, CO, and ethylene), which they were able to do unequivocally when the data was classified using linear discriminant analysis. The discriminating ability of this e-nose design was not impacted by the lengths or diameters of the nanowires used.

Microtubular optical microcavities from rolled-up ring resonators with subwavelength wall thicknesses have been fabricated by releasing prestressed SiO/SiO2 bilayer nanomembranes from photoresist sacrificial layers. Whispering gallery modes are observed in the photoluminescence spectra from the rolled-up nanomembranes, and their spectral peak positions shift significantly when measurements are carried out in different surrounding liquids, thus indicating excellent sensing functionality of these optofluidic microcavities. Analytical calculations as well as finite-difference time-domain simulations are performed to investigate the light confinement in the optical microcavities numerically and to describe the experimental mode shifts very well. A maximum sensitivity of 425 nm/refractive index unit is achieved for the microtube ring resonators, which is caused by the pronounced propagation of the evanescent field in the surrounding media due to the subwavelength wall thickness design of the microcavity. Our optofluidic sensors show high potential for lab-on-a-chip applications, such as real-time bioanalytic systems.

Central to most applications involving monolayer graphenes is its mechanical response under various stress states. To date most of the work reported is of theoretical nature and refers to tension and compression loading of model graphenes. Most of the experimental work is indeed limited to the bending of single flakes in air and the stretching of flakes up to typically ∼1% using plastic substrates. Recently we have shown that by employing a cantilever beam we can subject single graphenes to various degrees of axial compression. Here we extend this work much further by measuring in detail both stress uptake and compression buckling strain in single flakes of different geometries. In all cases the mechanical response is monitored by simultaneous Raman measurements through the shift of either the G or 2D phonons of graphene. Despite the infinitely small thickness of the monolayers, the results show that graphenes embedded in plastic beams exhibit remarkable compression buckling strains. For large length (l)-to-width (w) ratios (≥0.2) the buckling strain is of the order of −0.5% to −0.6%. However, for l/w < 0.2 no failure is observed for strains even higher than −1%. Calculations based on classical Euler analysis show that the buckling strain enhancement provided by the polymer lateral support is more than 6 orders of magnitude compared to that of suspended graphene in air.

This paper reports an effective method to enhance the surface plasmon resonance (SPR) on Ag films by using a thin Ni seed layer assisted deposition. Ag films with a thickness of about 50 nm were deposited by electron beam evaporation above an ultrathin Ni seed layer of ∼2 nm on both silicon and quartz substrates. The root-mean-square (rms) surface roughness and the correlation length have been reduced from >4 nm and 28 nm for a pure Ag film to ∼1.3 and 19 nm for Ag/Ni films, respectively. Both experimental and simulation results show that the Ag/Ni films exhibit an enhanced SPR over the pure Ag film with a narrower full width at half-maximum. Ag films with a Ge seed layer have also been prepared under the same conditions. The surface roughness can be reduced to less than 0.7 nm, but narrowing of the SPR curve is not observed due to increased absorptive damping in the Ge seed layer. Our results show that Ni acts as a roughness-diminishing growth layer for the Ag film while at the same time maintaining and enhancing the plasmonic properties of the combined structures. This points toward its use for low-loss plasmonic devices and optical metamaterials applications.

This paper describes a systematic comparison of the photoelectrochemical properties of mesoporous TiO2 films prepared by the two most prevalent templating methods: The use of preformed, crystalline nanoparticles is generally considered advantageous compared to the usage of molecular precursors such as TiCl4, since the latter requires a separate heat treatment at elevated temperature to induce crystallization. However, our photoelectrochemical experiments clearly show that sol−gel derived mesoporous TiO2 films cause an about 10 times higher efficiency for the water splitting reaction than their counterparts obtained from crystalline TiO2 nanoparticles. This result indicates that for electrochemical applications the performance of nanoparticle-based metal oxide films might suffer from insufficient electronic connectivity.

A method is presented to produce graphene dispersions, stabilized in water by the surfactant sodium cholate, at concentrations up to 0.3 mg/mL. The process uses low power sonication for long times (up to 400 h) followed by centrifugation to yield stable dispersions. The dispersed concentration increases with sonication time while the best quality dispersions are obtained for centrifugation rates between 500 and 2000 rpm. Detailed TEM analysis shows the flakes to consist of 1−10 stacked monolayers with up to 20% of flakes containing just one layer. The average flake consists of ∼4 stacked monolayers and has length and width of ∼1 μm and ∼400 nm, respectively. These dimensions are surprisingly stable under prolonged sonication. However, the mean flake length falls from ∼1 μm to ∼500 nm as the centrifugation rate is increased from 500 to 5000 rpm. Raman spectroscopy shows the flake bodies to be relatively defect-free for centrifugation rates below 2000 rpm. The dispersions can be easily cast into high-quality, free-standing films. The method extends the scope for scalable liquid-phase processing of graphene for a wide range of applications.

Photoluminescent NaYF4:Yb3+/Tm3+ nanocrystals are ideally suited for in vitro and in vivo photoluminescence (PL) bioimaging due to their virtue of near-infrared to near-infrared (NIR-to-NIR) upconversion (UC); they display PL with a peak at ∼800 nm if excited at ∼980 nm. Here, we report the synthesis of monodisperse NaYF4:Yb3+/Tm3+ nanocrystals of ultrasmall size (7−10 nm) with high UC efficiency. The intensity of their NIR UC emission was demonstrated to increase by up to 43 times along with an increase in the relative content of Yb3+ ions from 20 to 100%, with a corresponding decrease in the Y3+ content from 80 to 0%. The achieved ultrasmall NaYbF4:2% Tm3+ nanocrystals manifest NIR PL emission, which is 3.6 times more intense than that from 25−30 nm sized NaYF4:20% Yb3+/2% Tm3+ nanocrystals, previously synthesized and used for in vitro and in vivo bioimaging. An optimization of both size and UC PL efficiency of NIR-to-NIR nanocrystals provides us with highly efficient optical imaging probes for bioapplications.

The utilization of graphene oxide (GO) thin films as the hole transport and electron blocking layer in organic photovoltaics (OPVs) is demonstrated. The incorporation of GO deposited from neutral solutions between the photoactive poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) layer and the transparent and conducting indium tin oxide (ITO) leads to a decrease in recombination of electrons and holes and leakage currents. This results in a dramatic increase in the OPV efficiencies to values that are comparable to devices fabricated with PEDOT:PSS as the hole transport layer. Our results indicate that GO could be a simple solution-processable alternative to PEDOT:PSS as the effective hole transport and electron blocking layer in OPV and light-emitting diode devices.

We report a confocal Raman study on edges of single-layer graphene. It is found that edge orientations could be identified by G mode in addition to D mode. We observe that G mode at the edges of single-layer graphene exhibits polar behaviors and different edges such as zigzag- or armchair-dominated responses differently than the polarization of the incident laser. Moreover, G mode shows stiffening at zigzag-dominated edges, while it is softened at armchair-dominated ones. Our observations are in good agreement with recent theory (Sasaki, K. et al. J. Phys. Soc. Jpn. 2010, 79, 044603) and could be well-explained by the unique properties of pseudospin at graphene edges, which lead to asymmetry of Raman active modes and non-adiabatic processes (Kohn Anomaly) at different types of edges. This work could be useful for further study on the properties of the graphene edge and development of graphene-based devices.

Graphitic nanomaterials such as graphene layers (G) and single-wall carbon nanotubes (SWCNT) are potential candidates in a large number of biomedical applications. However, little is known about the effects of these nanomaterials on biological systems. Here we show that the shape of these materials is directly related to their induced cellular toxicity. Both G and SWCNT induce cytotoxic effects, and these effects are concentration- and shape-dependent. Interestingly, at low concentrations, G induced stronger metabolic activity than SWCNT, a trend that reversed at higher concentrations. Lactate dehydrogenase levels were found to be significantly higher for SWCNT as compared to the G samples. Moreover, reactive oxygen species were generated in a concentration- and time-dependent manner after exposure to G, indicating an oxidative stress mechanism. Furthermore, time-dependent caspase 3 activation after exposure to G (10 μg/mL) shows evidence of apoptosis. Altogether these studies suggest different biological activities of the graphitic nanomaterials, with the shape playing a primary role.

We report a facile strategy to synthesize the nanocomposite of Co3O4 nanoparticles anchored on conducting graphene as an advanced anode material for high-performance lithium-ion batteries. The Co3O4 nanoparticles obtained are 10−30 nm in size and homogeneously anchor on graphene sheets as spacers to keep the neighboring sheets separated. This Co3O4/graphene nanocomposite displays superior Li-battery performance with large reversible capacity, excellent cyclic performance, and good rate capability, highlighting the importance of the anchoring of nanoparticles on graphene sheets for maximum utilization of electrochemically active Co3O4 nanoparticles and graphene for energy storage applications in high-performance lithium-ion batteries.

Coordination of phenyldithiocarbamate (PTC) ligands to solution-phase colloidal CdSe quantum dots (QDs) decreases the optical band gap, Eg, of the QDs by up to 220 meV. These values of ΔEg are the largest shifts achieved by chemical modification of the surfaces of solution-phase CdSe QDs and are—by more than an order of magnitude in energy—the largest bathochromic shifts achieved for QDs in either the solution or solid phases. Measured values of ΔEg upon coordination to PTC correspond to an apparent increase in the excitonic radius of 0.26 ± 0.03 nm; this excitonic delocalization is independent of the size of the QD for radii, R = 1.1−1.9 nm. Density functional theory calculations indicate that the highest occupied molecular orbital of PTC is near resonant with that of the QD, and that the two have correct symmetry to exchange electron density (PTC is a π-donor, and the photoexcited QD is a π-acceptor). We therefore propose that the relaxation of exciton confinement occurs through delocalization of the photoexcited hole of the QD into the ligand shell.

Recently, the field-effect transistors (FETs) with graphene as the conducting channels have been used as a promising chemical and biological sensors. However, the lack of low cost and reliable and large-scale preparation of graphene films limits their applications. In this contribution, we report the fabrication of centimeter-long, ultrathin (1−3 nm), and electrically continuous micropatterns of highly uniform parallel arrays of reduced graphene oxide (rGO) films on various substrates including the flexible polyethylene terephthalate (PET) films by using the micromolding in capillary method. Compared to other methods for the fabrication of graphene patterns, our method is fast, facile, and substrate independent. In addition, we demonstrate that the nanoelectronic FETs based on our rGO patterns are able to label-freely detect the hormonal catecholamine molecules and their dynamic secretion from living cells.

Highly fluorescent, stable, water-soluble Ag nanoclusters have been successfully prepared via a convenient sonochemical approach using a simple polyelectrolyte, polymethylacrylic acid (PMAA), as a capping agent. The optical and fluorescence properties of the Ag nanoclusters can be easily controlled by varying the synthetic conditions, such as sonication time, stoichiometry of the carboxylate groups to Ag+, and polymer molecular weight.

Nanoscale assemblies that can be activated and controlled through external stimuli represent a next stage in multifunctional therapeutics. We report the formation, characterization, and release properties of bilayer-decorated magnetoliposomes (dMLs) that were prepared by embedding small hydrophobic SPIO nanoparticles at different lipid molecule to nanoparticle ratios within dipalmitoylphosphatidylcholine (DPPC) bilayers. The dML structure was examined by cryogenic transmission electron microscopy and differential scanning calorimetry, and release was examined by carboxyfluorescein leakage. Nanoparticle heating using alternating current electromagnetic fields (EMFs) operating at radio frequencies provided selective release of the encapsulated molecule at low nanoparticle concentrations and under physiologically acceptable EMF conditions. Without radio frequency heating, spontaneous leakage from the dMLs decreased with increasing nanoparticle loading, consistent with greater bilayer stability and a decrease in the effective dML surface area due to aggregation. With radio frequency heating, the initial rate and extent of leakage increased significantly as a function of nanoparticle loading and electromagnetic field strength. The mechanism of release is attributed to a combination of bilayer permeabilization and partial dML rupture.

We have observed large-amplitude coherent phonon oscillations of radial breathing modes (RBMs) in single-walled carbon nanotubes excited through the lowest-energy (E11) interband transitions. In contrast to the previously studied coherent phonons excited through higher-energy (E22) transitions, these RBMs show comparable intensities between (n−m) mod 3 = +1 and −1 nanotubes. We also find the novel observation of RBMs excited over an excitation range of ∼300 meV above the E11 transition, which we attribute to possible resonance with phonon sidebands of the lowest optical transition, arising from strong exciton−phonon coupling.

For decades, ethanol has been in use as a fuel for the storage of solar energy in an energy-dense, liquid form. Over the past decade, the ability to reform ethanol into hydrogen gas suitable for a fuel cell has drawn interest as a way to increase the efficiency of both vehicles and stand-alone power generators. Here we report the use of extremely small nanocrystalline materials to enhance the performance of 1% Rh/10% Ni@CeO2 catalysts in the oxidative steam reforming of ethanol with a ratio of 1.7:1:10:11 (air/EtOH/water/argon) into hydrogen gas, achieving 100% conversion of ethanol at only 300 °C with 60% H2 in the product stream and less than 0.5% CO. Additionally, nanocrystalline 10% Ni@CeO2 was shown to achieve 100% conversion of ethanol at 400 °C with 73% H2, 2% CO, and 2% CH4 in the product stream. Finally, we demonstrate the use of biological templating on M13 to improve the resistance of this catalyst to deactivation over 52 h tests at high flow rates (120 000 h−1 GHSV) at 450 °C. This study suggests that the use of highly nanocrystalline, biotemplated catalysts to improve activity and stability is a promising route to significant gains over traditional catalyst manufacture methods.

A detailed study on the relaxation mechanisms of higher cage fullerene sizes is done as a prerequisite for studies of the influence of the endohedral structures on fullerene cage carbon relaxation. Recent studies of the dynamic behavior of C60 and C70 in aromatic solvents and CS2 solution show the influence of the shape and the symmetry of the cage to be highly important as well as the influence of the solvent to be negligible. As higher fullerene cages have more than one stable isomer, the isolation of isomeric pure structures is of high importance for a detailed study of the dynamic behavior of such fullerenes. Here we investigated the three higher fullerene cage isomers D2-C76, C2v(3)-C78, and D2-C80 with respect to the relaxation rate of the carbons measured in their temperature dependence. Thus, we study the influence on the relaxation of the carbons and the dynamic behavior of these fullerenes in solution. Besides the diffusion dependence on the shape of the carbon cage, the relaxation behavior at lower temperatures is found to be dependent on the difference in chemical shift anisotropy within the carbon cage. This difference is originated from the changes of symmetry and results in polarization of electron density. Furthermore, the mobility of the carbons is influenced by their pyramidalization.

The use of mixed selective solvents provides an effective means to control self-assembly of the all-conjugated diblock copolymer poly(3-butylthiophene)-b-poly(3-hexylthiophene) (P3BHT) into nanostructured morphologies. The solvent and temperature effects on the self-assembly of P3BHT during cooling and subsequent crystallization were explored for the first time. Depending on the poor/good solvent ratio (i.e., anisole/chloroform), P3BHT chains experience different kinetic pathways, yielding nanowires at a low anisole/chloroform ratio (≤2:1), and nanorings coexisted with some nanowires at a high anisole/chloroform ratio (≥6:1). The nanowires are formed as a direct consequence of strong interchain π−π stacking, while the formation of nanorings is governed by solvophobic interactions between conjugated blocks and the poor solvent anisole to minimize the unfavorable contacts between the P3BT block (∼50 °C) and later P3HT (below 35 °C) block and anisole.

We report a new single-step method to directly imprint nanometer-scale structures on photoreactive organic semiconductors. A surface relief grating is spontaneously formed when a light-emitting, liquid crystalline, and semiconducting thin film is irradiated by patterned light generated using a phase mask. Grating formation requires no postannealing nor wet etching so there is potential for high-throughput fabrication. The structured film is cross-linked for robustness. Gratings deeper than the original film thickness are made with periods as small as 265 nm. Grating formation is attributed to mass transfer, enhanced by self-assembly, from dark to illuminated regions. A photovoltaic device incorporating the grating is discussed.

Acquiring the temperature of a single living cell is not a trivial task. In this paper, we devise a novel nanothermometer, capable of accurately determining the temperature of solutions as well as biological systems such as HeLa cancer cells. The nanothermometer is based on the temperature-sensitive fluorescence of NaYF4:Er3+,Yb3+ nanoparticles, where the intensity ratio of the green fluorescence bands of the Er3+ dopant ions (2H11/2 → 4I15/2 and 4S3/2 → 4I15/2) changes with temperature. The nanothermometers were first used to obtain thermal profiles created when heating a colloidal solution of NaYF4:Er3+,Yb3+ nanoparticles in water using a pump−probe experiment. Following incubation of the nanoparticles with HeLa cervical cancer cells and their subsequent uptake, the fluorescent nanothermometers measured the internal temperature of the living cell from 25 °C to its thermally induced death at 45 °C.

Surface-enhanced Raman scattering (SERS) labels and probes consisting of gold and silver nanoaggregates and attached reporter molecules can be identified by the Raman signature of the reporter molecule. At the same time, SERS hybrid probes deliver sensitive molecular structural information on their nanoenvironment. Here we demonstrate full exploitation of the multifunctional and multiplexing capabilities inherent to such nanoprobes by applying cluster methods and principal components approaches for discrimination beyond the visual inspection of individual spectra that has been practiced so far. The reported results indicate that fast, multivariate evaluation of whole sets of multiple probes is feasible. Spectra of five different reporters were shown to be separable by hierarchical clustering and by principal components analysis (PCA). In a duplex imaging approach in live cells, hierarchical cluster analysis, K-means clustering, and PCA were used for imaging the positions of different types of SERS probes along with the spectral information from cellular constituents. Parallel to cellular imaging experiments, cytotoxicity of the SERS hybrid probes containing aromatic thiols as reporters is assessed. The reported results suggest multiplexing applications of the nontoxic SERS nanoprobes in high density sensing and imaging in complex biological structures.

Disk-shaped semiconductor nanostructures provide enhanced architectures for low-threshold whispering gallery mode (WGM) lasing with the potential for on-chip nanophotonic integration. Unlike cavities that lase via Fabry−Perot modes, WGM structures utilize low-loss, total internal reflection of the optical mode along the circumference of the structure, which effectively reduces the volume of gain material required for lasing. As a result, circularly resonant cavities provide much higher quality (Q) factors than lower reflection linear cavities, which makes nanodisks an ideal platform to investigate lasing nanostructures smaller than the free-space wavelength of light (i.e., subwavelength laser). Here we report the bottom-up synthesis and single-mode lasing properties of individual ZnO disks with diameters from 280 to 900 nm and show finite difference time domain (FDTD) simulations of the whispering gallery mode inside subwavelength diameter disks. These results demonstrate ultraviolet WGM lasing in chemically synthesized, isolated nanostructures with subwavelength diameters.

Millions of teeth are saved each year by root canal therapy. Although current treatment modalities offer high levels of success for many conditions, an ideal form of therapy might consist of regenerative approaches in which diseased or necrotic pulp tissues are removed and replaced with healthy pulp tissue to revitalize teeth. Melanocortin peptides (α-MSH) possess anti-inflammatory properties in many acute and chronic inflammatory models. Our recent studies have shown that α-MSH covalently coupled to poly-l-glutamic acid (PGA-α-MSH) retains anti-inflammatory properties on rat monocytes. This study aimed to define the effects of PGA-α-MSH on dental pulp fibroblasts. Lipopolysaccharide (LPS)-stimulated fibroblasts incubated with PGA-α-MSH showed an early time-dependent inhibition of TNF-α, a late induction of IL-10, and no effect on IL-8 secretion. However, in the absence of LPS, PGA-α-MSH induced IL-8 secretion and proliferation of pulp fibroblasts, whereas free α-MSH inhibited this proliferation. Thus, PGA-α-MSH has potential effects in promoting human pulp fibroblast adhesion and cell proliferation. It can also reduce the inflammatory state of LPS-stimulated pulp fibroblasts observed in gram-negative bacterial infections. These effects suggest a novel use of PGA-α-MSH as an anti-inflammatory agent in the treatment of endodontic lesions. To better understand these results, we have also used the multilayered polyelectrolyte films as a reservoir for PGA-α-MSH by using not only PLL (poly-l-lysine) but also the Dendri Graft poly-l-lysines (DGLG4) to be able to adsorb more PGA-α-MSH. Our results indicated clearly that, by using PGA-α-MSH, we increase not only the viability of cells but also the proliferation. We have also analyzed at the nanoscale by atomic force microscopy these nanostructured architectures and shown an increase of thickness and roughness in the presence of PGA-α-MSH incorporated into the multilayered film (PLL-PGA-α-MSH)10 or (DGLG4-PGA-α-MSH)10 in accordance with the increase of the proliferation of the cells growing on the surface of these architectures. We report here the first use of nanostructured and functionalized multilayered films containing α-MSH as a new active biomaterial for endodontic regeneration.

We report on the ferromagnetism of conducting filaments formed in a NiO thin film, which exhibited a typical bistable resistive switching characteristic. The NiO thin film showed an antiferromagnetic hysteresis loop for a high resistive state (ROFF). However, for a low resistive state (RON), the conducting filaments exhibited a ferromagnetic hysteresis loop for the field cooling. The ferromagnetic hysteresis behavior of the RON state reveals switchable exchange coupling between the ferromagnetic Ni conducting filaments and the antiferromagnetic NiO layer.

Bacterial virus phi29 genomic DNA is packaged into a procapsid shell with the aid of a motor containing a 12-subunit connector channel and a hexameric pRNA (packaging RNA) ring. The wide end, or the C-terminus, of the cone-shaped connector is embedded within the procapsid shell, whereas the narrow end, or N-terminus, extends outside of the procapsid, providing a binding location for pRNA. Recently, we have reported the mechanism of in vivo assembly of an ellipsoid nanoparticle with seven connectors through an interaction among a peptide tag. Here we report the formation of a similar nanoparticle in vitro via the addition of DNA or RNA oligos to connector proteins. Free connectors guided by one or two copies of oligonucleotides were assembled into a rosette structure containing 60 subunits of reengineered proteins. The number of oligonucleotides within the particle is length-dependent but sequence-independent. Reversible shifting between the 12- and 60-subunit nanoparticles (between individual connectors and rosette structures, respectively) was demonstrated by the alternative addition of oligonucleotides and the treatment of ribonuclease, suggesting a potential application as a switch or regulator in nanobiotechnology. This advancement allows for a simple method to produce multivalent nanoparticles that contain five 12-unit nanoparticles with defined structure and stoichiometry. That is, it will be possible to assemble nanoparticles in vitro with the combination of 60 assortments of ligands, tags, therapeutic drugs, and diagnostic moieties for multivalent delivery or enhancement of signal detection in nanotechnological and nanomedicinal applications.

Vertically aligned ZnO/CdTe core−shell nanocable arrays-on-indium tin oxide (ITO) are fabricated by electrochemical deposition of CdTe on ZnO nanorod arrays in an electrolyte close to neutral pH. By adjusting the total charge quantity applied during deposition, the CdTe shell thickness can be tuned from several tens to hundreds of nanometers. The CdTe shell, which has a zinc-blende structure, is very dense and uniform both radially and along the axial direction of the nanocables, and forms an intact interface with the wurtzite ZnO nanorod core. The absorption of the CdTe shell above its band gap (∼1.5 eV) and the type II band alignment between the CdTe shell and the ZnO core, respectively, demonstrated by absorption and photoluminescence measurements, make a nanocable array-on-ITO architecture a promising photoelectrode with excellent photovoltaic properties for solar energy applications. A photocurrent density of ∼5.9 mA/cm2 has been obtained under visible light illumination of 100 mW cm−2 with zero bias potential (vs saturated calomel electrode). The neutral electrodeposition method can be generally used for plating CdTe on nanostructures made of different materials, which would be of interest in various applications.

We studied the fluorescence enhancement of a dye-loaded polyphenylene dendrimer in a gap of 2−3 nm between a silver film and single silver particles with an average diameter of 80 nm. This sphere-on-plane geometry provides a controllable plasmonic resonator with a defined dye position. A strong fluorescence signal was seen from all particles, which was at least 1000 times stronger than the signal from the plane dye-coated metal surface. The fluorescence emission profile varied between the particles and showed light emission at higher energies than the free dye, which we assigned to hot luminescence. The maximum fluorescence emission peak shifted along with the scattering maximum of the plasmonic resonance. Two classes of scattering resonators could be distinguished. Up to a significant line-broadening, the response of the “sphere-on-plane”-like cases resembled the theoretical prediction for a perfect sphere-on-plane geometry. Resonators which deviate strongly from this ideal scenario were also found. Electron microscopy did not show significant differences between these two classes, suggesting that the variations in the optical response are due to nanoscale variations of shape and roughness in the gap region. The strong modifications of the dye emission spectrum suggested the presence of physical mechanisms at very small metal/dye separations, which are beyond a simple wavelength-dependent enhancement factor.

The electrical properties of random networks of single-wall carbon nanotubes (SWNTs) obtained by inkjet printing are studied. Water-based stable inks of functionalized SWNTs (carboxylic acid, amide, poly(ethylene glycol), and polyaminobenzene sulfonic acid) were prepared and applied to inkjet deposit microscopic patterns of nanotube films on lithographically defined silicon chips with a back-side gate arrangement. Source−drain transfer characteristics and gate-effect measurements confirm the important role of the chemical functional groups in the electrical behavior of carbon nanotube networks. Considerable nonlinear transport in conjunction with a high channel current on/off ratio of ∼70 was observed with poly(ethylene glycol)-functionalized nanotubes. The positive temperature coefficient of channel resistance shows the nonmetallic behavior of the inkjet-printed films. Other inkjet-printed field-effect transistors using carboxyl-functionalized nanotubes as source, drain, and gate electrodes, poly(ethylene glycol)-functionalized nanotubes as the channel, and poly(ethylene glycol) as the gate dielectric were also tested and characterized.

Cotton fabric was treated with flame-retardant coatings composed of branched polyethylenimine (BPEI) and sodium montmorillonite (MMT) clay, prepared via layer-by-layer (LbL) assembly. Four coating recipes were created by exposing fabric to aqueous solutions of BPEI (pH 7 or 10) and MMT (0.2 or 1 wt %). BPEI pH 10 produces the thickest films, while 1 wt % MMT gives the highest clay loading. Each coating recipe was evaluated at 5 and 20 bilayers. Thermogravimetric analysis showed that coated fabrics left as much as 13% char after heating to 500 °C, nearly 2 orders of magnitude more than uncoated fabric, with less than 4 wt % coming from the coating itself. These coatings also reduced afterglow time in vertical flame tests. Postburn residues of coated fabrics were examined with SEM and revealed that the weave structure and fiber shape in all coated fabrics were preserved. The BPEI pH 7/1 wt % MMT recipe was most effective. Microcombustion calorimeter testing showed that all coated fabrics reduced the total heat release and heat release capacity of the fabric. Fiber count and strength of uncoated and coated fabric are similar. These results demonstrate that LbL assembly is a relatively simple method for imparting flame-retardant behavior to cotton fabric. This work lays the foundation for using these types of thin film assemblies to make a variety of complex substrates (foam, fabrics, etc.) flame resistant.

We report exceptional nanoscale wear and fouling resistance of ultrananocrystalline diamond (UNCD) tips integrated with doped silicon atomic force microscope (AFM) cantilevers. The resistively heated probe can reach temperatures above 600 °C. The batch fabrication process produces UNCD tips with radii as small as 15 nm, with average radius 50 nm across the entire wafer. Wear tests were performed on substrates of quartz, silicon carbide, silicon, or UNCD. Tips were scanned for more than 1 m at a scan speed of 25 μm s−1 at temperatures ranging from 25 to 400 °C under loads up to 200 nN. Under these conditions, silicon tips are partially or completely destroyed, while the UNCD tips exhibit little or no wear, no signs of delamination, and exceptional fouling resistance. We demonstrate nanomanufacturing of more than 5000 polymer nanostructures with no deterioration in the tip.

The reaction and diffusion of molecules across barriers and through crowded environments is integral to biological system function and to separation technologies. Ordered, microfabricated post arrays are a promising route to creating synthetic barriers with controlled chemical and physical characteristics. They can be used to create crowded environments, to mimic aspects of cellular membranes, and to serve as engineered replacements of polymer-based separation media. Here, the translational diffusion of fluorescein isothiocyante and various forms of green fluorescent protein (GFP), including “supercharged” variants, are examined in a silicon-based post array environment. The technique of fluorescence recovery after photobleaching (FRAP) is combined with analytical approximations and numerical simulations to assess the relative effects of reaction and diffusion on molecular transport, respectively. FRAP experiments were conducted for 64 different cases where the molecular species, the density of the posts, and the chemical surface charge of the posts were varied. In all cases, the dense packing of the posts hindered the diffusive transport of the fluorescent species. The supercharged GFPs strongly interacted with oppositely charged surfaces. With similar molecular and surface charges, transport is primarily limited by hindered diffusion. For conventional, enhanced GFP in a positively charged surface environment, transport was limited by the coupled action of hindered diffusion and surface interaction with the posts. Quantification of the size-, space-, time-, and charge-dependent translational diffusion in the post array environments can provide insight into natural processes and guide the design and development of selective membrane systems.

We demonstrate controllable and gate-tunable negative differential resistance in carbon nanotube field-effect transistors, at room temperature and at 4.2 K. This is achieved by effectively creating quantum dots along the carbon nanotube channel by patterning the underlying, high-κ gate oxide. The negative differential resistance feature can be modulated by both the gate and the drain-source voltage, which leads to more than 20% change of the current peak-to-valley ratio. Our approach is fully scalable and opens up a possibility for a new class of nanoscale electronic devices using negative differential resistance in their operation.

Understanding the nanoparticle−cell interaction is critical for the safe development of nanomaterials. Herein, we explore the impact of three metal oxide nanoparticles, nonporous Stöber SiO2, mesoporous SiO2, and nonporous anatase TiO2 nanoparticles, on primary culture mast cells. Using transmission electron microscopy and inductively coupled plasma atomic emission spectroscopy, we demonstrate that each class of nanoparticle is internalized by the mast cells, localizing primarily in the secretory granules, with uptake efficiency increasing in the following order: nonporous SiO2 < porous SiO2 < nonporous TiO2 nanoparticles. The influence of nanoparticle-laden granules was assessed using carbon-fiber microelectrode amperometry measurements that reveal functional changes in chemical messenger secretion from mast cell granules. Both nonporous and porous SiO2 nanoparticles cause a decrease in the number of molecules released per granule, with nonporous SiO2 also inducing a decrease in the amperometric spike frequency and, therefore, having a larger impact on cell function. As the two classes of SiO2 nanoparticles vary only in their porosity, these results suggest that, while the mesoporous SiO2 has a drastically larger total surface area due to the pores, the cell-contactable surface area, which is higher for the nonporous SiO2, is more important in determining a nanoparticles’ cellular impact. In comparison, exposure to nonporous TiO2 slows the kinetics of secretion without altering the number of molecules released from the average granule. The varying immune cell response following exposure to nonporous SiO2 and nonporous TiO2 indicates that the nanoparticle−cell interactions are also modulated by surface chemistry.

Colloidal quantum dot (CQD) photovoltaics combine low-cost solution processability with quantum size-effect tunability to match absorption with the solar spectrum. Rapid recent advances in CQD photovoltaics have led to impressive 3.6% AM1.5 solar power conversion efficiencies. Two distinct device architectures and operating mechanisms have been advanced. The first—the Schottky device—was optimized and explained in terms of a depletion region driving electron−hole pair separation on the semiconductor side of a junction between an opaque low-work-function metal and a p-type CQD film. The second—the excitonic device—employed a CQD layer atop a transparent conductive oxide (TCO) and was explained in terms of diffusive exciton transport via energy transfer followed by exciton separation at the type-II heterointerface between the CQD film and the TCO. Here we fabricate CQD photovoltaic devices on TCOs and show that our devices rely on the establishment of a depletion region for field-driven charge transport and separation, and that they also exploit the large bandgap of the TCO to improve rectification and block undesired hole extraction. The resultant depleted-heterojunction solar cells provide a 5.1% AM1.5 power conversion efficiency. The devices employ infrared-bandgap size-effect-tuned PbS CQDs, enabling broadband harvesting of the solar spectrum. We report the highest open-circuit voltages observed in solid-state CQD solar cells to date, as well as fill factors approaching 60%, through the combination of efficient hole blocking (heterojunction) and very small minority carrier density (depletion) in the large-bandgap moiety.

A simple density gradient ultracentrifuge separation method has been developed for sorting chemically modified graphene (CMG) by sheet size and surface chemistry in just a few minutes. By optimizing the parameters, including the density gradient and centrifugation time, CMG sheets with specific size ranges and optical properties can be targeted selectively. UV−vis absorbance and photoluminescence spectra revealed the properties of separated CMG samples are highly dependent on their sheet size and degree of oxidation. A possible mechanism for the separation is discussed.

We report the design of highly efficient optical antennas employing a judicious synthesis of metallic and dielectric materials. In the proposed scheme, a pair of metallic coupled nanoparticles permits large enhancements in both excitation strength and radiative decay rates, while a high refractive index dielectric microsphere is employed to efficiently collect light without spoiling the emitter quantum efficiency. Our simulations indicate potential fluorescence rate enhancements of 3 orders of magnitude over the entire optical frequency range.

The phosphorescent Ir(III) complexes were modified by allylation and consecutive hydrosilylation, and covalently incorporated into the silica nanoparticles by hydrolysis and condensation reaction with TEOS. These nanoparticles showed an excellent photochemical and thermal stability, and a very high luminescent efficiency due to the blocking of O2 quenching and suppression of energy transfer through the amorphous silica solid solution. The limited mobility of complexes in the silica matrix also resulted in a decrease in the vibration relaxation and restrained the nonradiative decay. It is expected that these photostable and very efficient phosphorescent nanoparticles can be used in various fields ranging from nanobiotechnology to nanoengineering materials, where long-term stability with the high luminescent efficiency is required. As an example of the use of excellent photostability, a preliminary test result in which they are used as a color converter in a light emitting diode (LED) is also discussed.

We report a systematic investigation of the optically excited vibrations in monolayer-protected gold clusters capped with hexane thiolate as a function of the particle size in the range of 1.1−4 nm. The vibrations were excited and monitored in transient absorption experiments involving 50 fs light pulses. For small quantum-sized clusters (≤2.2 nm), the frequency of these vibrations has been found to be independent of cluster size, while for larger clusters (3 and 4 nm), we did not observe detectable optically excited vibrations in this regime. Possible mechanisms of excitation and detection of the vibrations in nanoclusters in the course of the transient absorption are discussed. The results of the current investigation support a displacive excitation mechanism associated with the presence of finite optical energy gap in the quantum-sized nanoclusters. Observed vibrations provide a new valuable diagnostic tool for the investigations of quantum size effects and structural studies in metal nanoclusters.

In this paper, the synthesis of gold@gold(I)−thiolate core@shell nanoparticles is described for the first time. The chemical nature and structure of these nanoparticles were characterized by a multi-technique approach. The prepared particles consist of gold metallic cores, about 1 nm in size, surrounded by stable gold(I)−thiomalate shells (Au@Au(I)−TM). These nanoparticles could be useful in medicine due to the interesting properties that gold(I)−thiomalate has against rheumatoid arthritis. Furthermore, the described results give new insights in the synthesis and characterization of metallic and core@shell nanoparticles.

Lattice defects in carbon nanotubes and graphene are created by focusing an electron beam in a scanning transmission electron microscope onto a 0.1 nm spot on the objects. Metal atoms migrating on the graphenic surfaces are observed to be trapped by these defects. Depending on the size of the defect, single metal atoms or clusters of several atoms can be localized in or on nanotubes or graphene layers. Subsequent escape of the metal atoms from the trapping centers gives information about the bonding between the metal atom and the defect. The process of trapping and detrapping is studied in a temperature range of 20−670 °C. The technique allows one to place metal atoms with almost atomic precision in graphenic structures and to create a predefined pattern of foreign atoms in graphene or carbon nanotubes.

In this work, we have studied the adsorption and diffusion of large functionalized organic molecules on an insulating ionic surface at room temperature using a noncontact atomic force microscope (NC-AFM) and theoretical modeling. Custom designed syn-5,10,15-tris(4-cyanophenylmethyl)truxene molecules are adsorbed onto the nanoscale structured KBr(001) surface at low coverages and imaged with atomic and molecular resolution with the NC-AFM. The molecules are observed rapidly diffusing along the perfect monolayer step edges and immobilized at monolayer kink sites. Extensive atomistic simulations elucidate the mechanisms of adsorption and diffusion of the molecule on the different surface features. The results of this study suggest methods of controlling the diffusion of adsorbates on insulating and nanostructured surfaces.

We present a novel binder-free multiwall carbon nanotube (MWCNT) structure as an anode in Li ion batteries. The interface-controlled MWCNT structure, synthesized through a two-step process of catalyst deposition and chemical vapor deposition (CVD) and directly grown on a copper current collector, showed very high specific capacity, almost three times as that of graphite, excellent rate capability even at a charging/discharging rate of 3 C, and no capacity degradation up to 50 cycles. Significantly enhanced properties of this anode could be related to high Li ion intercalation on the carbon nanotube walls, strong bonding with the substrate, and excellent conductivity.

The structures of self-assembled monolayers formed by chemisorption of octadecanethiol onto the surfaces of GaAs(001), (110), (111-A)-Ga, and (111-B)-As have been characterized in detail by a combination of X-ray photoelectron, near-edge X-ray absorption fine structure, and infrared spectroscopies and grazing incidence X-ray diffraction. In all cases, the molecular lattices are ordered with hexagonal symmetry, even for the square and rectangular intrinsic substrate (001) and (110) lattices, and the adsorbate lattice spacings are all incommensurate with their respective intrinsic substrate lattices. These results definitively show that the monolayer organization is driven by intermolecular packing forces to assemble in a hexagonal motif, such as would occur in the approach to a limit for an energetically featureless surface. The accompanying introduction of strain into the soft substrate surface lattice via strong S substrate bonds forces the soft substrate lattice to compliantly respond, introducing quasi-2D strain. A notably poorer organization for the (111-A)-Ga case compared to the (111-B)-As and other faces indicates that that the Ga-terminated surface lattice is more resistant to adsorbate packing-induced stress. Overall, the results show that surface molecular self-assembly must be considered as a strongly cooperative process between the substrate surface and the adsorbate and that inorganic substrate surfaces should not be considered as necessarily rigid when strong intermolecular adsorbate packing forces are operative.

The order of magnitude of Raman differential cross sections of radial breathing modes (RBMs) of individual carbon nanotubes is measured for 633 and 785 nm laser excitations. This is shown by both a calibration applied to previously published data from other authors at 785 nm and our own measurements of individual nanotubes at 633 nm excitation. We find typical values of differential cross sections of RBMs to be on the order of ∼10−22 cm2/sr for resonant nanotubes on a silicon substrate. This study therefore provides a rigorous quantification of the accepted view that Raman cross sections of carbon nanotubes are “huge”.

Anodic aluminum oxide (AAO) containing arrays of aligned cylindrical nanopores infiltrated with polymers is a well-defined model system for the study of hypersound propagation in polymer nanocomposites. Hypersonic phononic properties of AAO/polymer nanocomposites such as phonon localization and anisotropic sound propagation can be tailored by adjusting elastic contrast and density contrast between the components. Changes in density and elastic properties of the component located in the nanopores induced by phase transitions allow reversible modification of the phononic band structure and mode switching. As example in case, the crystallization and melting of poly(vinylidene difluoride) inside AAO was investigated.

This paper presents a systematic investigation on the incorporation of chemical exfoliation graphene sheets (GS) in TiO2 nanoparticle films via a molecular grafting method for dye-sensitized solar cells (DSSCs). By controlling the oxidation time in the chemical exfoliation process, both high conductivity of reduced GS and good attachment of TiO2 nanoparticles on the GS were achieved. Uniform GS/TiO2 composite films with large areas on conductive glass were prepared by electrophoretic deposition, and the incorporation of GS significantly improved the conductivity of the TiO2 nanoparticle film by more than 2 orders of magnitude. Moreover, the power conversion efficiency for DSSC based on GS/TiO2 composite films is more than 5 times higher than that based on TiO2 alone, indicating that the incorporation of GS is an efficient means for enhancing the photovoltaic (PV) performance. The better PV performance of GS/TiO2 DSSC is also attributed to the better dye loading of GS/TiO2 film than that of TiO2 film. The effect of GS content on the PV performances was also investigated. It was found that the power conversion efficiency increased first and then decreased with the increasing of GS concentration due to the decrease in the transmittance at high GS content. Further improvements can be expected by fully optimizing fabrication conditions and device configuration, such as increasing dye loading via thicker films. The present synthetic strategy is expected to lead to a family of composites with designed properties.

Au nanocrystals (NCs) with different crystalline structures and related morphologies are unselectively synthesized using an organometallic route. The acoustic vibrations of these NCs are studied by plasmon mediated low-frequency Raman scattering (LFRS). A splitting of the quadrupolar vibration mode is pointed out in the LFRS spectrum. Comparison of the measured frequencies with calculations and careful examination of the NCs morphologies by transmission electron microscopy ascertain this splitting as being an effect of crystallinity. The excitation dependence of the LFRS spectra is interpreted by the shape-selection of the NCs via plasmon−vibration coupling. These results give new insights into the crystallinity influence on both the vibrations of the NCs and their coupling with plasmons and demonstrate the relevance of elastic anisotropy in monodomain NCs.

This paper reports novel electromechanical behavior for a natural biopolymer film due to the incorporation of a conductive carbon nanotube network. Through simple solution blending and casting, high weight fraction single-walled carbon nanotube−chitosan composite films were fabricated and exhibited electromechanical actuation properties with motion controlled by low alternating voltage stimuli in atmospheric conditions. Of particular interest and importance is that the displacement output imitated perfectly the electrical input signal in terms of frequency (<10 Hz) and waveform. Operational reliability was confirmed by stable vibration testing in air for more than 3000 cycles. Proposed electrothermal mechanism considering the alternating current-induced periodic thermal expansion and contraction of the composite film was discussed. The unique actuation performance of the carbon nanotube−biopolymer composite, coupled with ease of fabrication, low driven voltage, tunable vibration, reliable operation, and good biocompatibility, shows great possibility for implementation of dry actuators in artificial muscle and microsystems for biomimetic applications.

Water-soluble, polyelectrolyte-grafted multiwalled carbon nanotubes (MWCNTs), MWCNT-g-PSSNa, were synthesized using a “grafting to” route. MWCNT-g-PSSNa thin films fabricated by an electrostatic spray (e-spray) technique were used as the counter electrode (CE) for dye-sensitized solar cells (DSSCs). The e-sprayed MWCNT-g-PSSNa thin-film-based CEs (MWCNT-CE) were uniform over a large area, and the well-exfoliated MWCNTs formed highly interconnected network structures. The electrochemical catalytic activity of the MWCNT-CE at different thicknesses was investigated. The MWCNT-g-PSSNa thin film showed high efficiency as a CE in DSSCs. The power conversion efficiency (PCE) of the DSSCs using the MWCNT-g-PSSNa thin-film-based CE (DSSC-MWCNT) was >6% at a CE film thickness of ∼0.3 μm. The optimum PCE was >7% at a film thickness of ∼1 μm, which is 20−50 times thinner than conventional carbon-based CE. The charge transfer resistance at the MWCNT-CE/electrolyte interface was 1.52 Ω cm2 at a MWCNT-CE thickness of 0.31 μm, which is lower than that of a Pt-CE/electrolyte interface, 1.78 Ω cm2. This highlights the potential for the low-cost CE fabrication of DSSCs using a facile deposition technique from an environmentally “friendly” solution at low temperatures.

Complementary electronic properties and a tendency to form sharp graphene−graphane interfaces open tantalizing possibilities for two-dimensional nanoelectronics. First-principles density functional and tight-binding calculations show that graphane can serve as natural host for graphene quantum dots, clusters of vacancies in the hydrogen sublattice. Their size n, shape, and stability are governed by the aromaticity and interfaces, resulting in formation energies ∼1/√n eV/atom and preference to hexagonal clusters congruent with lattice hexagons (i.e., with armchair edge). Clusters exhibit large gaps ∼15/√n eV with size dependence typical for confined Dirac fermions.

A novel quasi-two-dimensional phase of carbon and the formation of a metastable hexagonal phase of single-walled carbon nanotubes (SWCNTs) have been investigated using density functional theory (DFT) by subjecting the SWCNT bundles to hydrostatic pressure. The chirality of the nanotubes determines the breaking of symmetry of the nanotubes under compression. Interestingly SWCNTs are found to undergo a mixture of sp2 and sp3 hybridization and are found to form novel interacting quasi-two-dimensional sheets of interlinked SWCNTs under hydrostatic pressure. Symmetry breaking, leading to the formation of highly directional bonds at stressed edges, is found to play an important role in the interlinking of the nanotubes. (3n + 3, 3n + 3) SWCNTs are found to acquire a hexagonal cross-section when subjected to hydrostatic pressures. The opening of a pseudogap is observed for small as well as large diameter armchair SWCNTs in nanotube bundles. Equilibrium separations calculated using the Leonard-Jones potentials indicate excellent agreement with the predictions of density functional calculations and experimental observations.

Our study demonstrates that the C69N azafullerene can be encapsulated inside single-walled carbon nanotubes (SWNTs), which is confirmed by TEM, UV−vis−IR spectroscopy, Raman spectroscopy, and UPS. The electrical transport properties of SWNTs are found to change drastically due to the encapsulated C69N azafullerene. Our experimental results indicate that C69N encapsulated SWNTs show the high-performance n-type behavior compared with p-type characteristics of pristine SWNTs and C70 encapsulated SWNTs. This n-type transport characteristic can be explained by the charge transfer effect between SWNTs and encapsulated C69N, which can easily lose an electron. The unique electronic properties of C69N encapsulated SWNTs make them potentially useful in many applications in engineering functional nanodevices.

Few-layer graphenes (FLG) produced by dispersion and exfoliation of graphite in N-methylpyrrolidone were successfully functionalized using the 1,3-dipolar cycloaddition of azomethine ylides. The amino functional groups attached to graphene sheets were quantified by the Kaiser test. These amino groups selectively bind to gold nanorods, which were introduced as contrast markers for the identification of the graphene reactive sites. The interaction between gold nanorods and functionalized graphene was followed by UV−vis spectroscopy. The presence of the organic groups was confirmed by X-ray photoelectron spectroscopy and thermogravimetric analysis. The sheets were characterized by transmission electron microscopy, demonstrating the presence of gold nanorods distributed uniformly all over the graphene surface. This observation indicates that reaction has taken place not just at the edges but also at the internal C═C bonds of graphene. Our results identify exfoliated graphene as a considerably more reactive structure than graphite and hence open the possibility to control the functionalization for use as a scaffold in the construction of organized composite nanomaterials.