In this review, we describe the creation of a large database of thermoelectric materials prepared by abstracting information from over 100 publications. The database has over 18 000 data points from multiple classes of compounds, whose relevant properties have been measured at several temperatures. Appropriate visualization of the data immediately allows certain insights to be gained with regard to the property space of plausible thermoelectric materials. Of particular note is that any candidate material needs to display an electrical resistivity value that is close to 1 mΩ cm at 300 K, that is, samples should be significantly more conductive than the Mott minimum metallic conductivity. The Herfindahl–Hirschman index, a commonly accepted measure of market concentration, has been calculated from geological data (known elemental reserves) and geopolitical data (elemental production) for much of the periodic table. The visualization strategy employed here allows rapid sorting of thermoelectric compositions with respect to important issues of elemental scarcity and supply risk.

This work characterizes the nucleation and growth kinetics of zinc oxide (ZnO) precipitated from aqueous hexamethylenetetramine (HMTA) zinc nitrate (Zn(NO3)2) solutions observed by in situ and ex situ transmission electron microscopy. Quantitative comparisons between in situ beam-induced precipitation, in situ thermally activated precipitation, ex situ thermally activated precipitation, and ex situ electrochemistry provide insights into the rate limiting mechanism and the chemistry governing the reactions. All experiments indicate that isotropic ZnO precipitates directly from solution. These particles begin to aggregate and grow anisotropically shortly after nucleation. The conversion to anisotropic growth does not rely on coalescence despite the fact that the two are often observed to occur in concert. The results indicate that the reaction pathway for in situ beam-induced growth more closely mimics ex situ electrochemistry than ex situ chemistry. In situ and ex situ thermally activated growth processes proceed in a similar manner, although particle transport and aggregation are limited by the in situ geometry.

We studied the growth of TiO2 by liquid injection atomic layer deposition (ALD) utilizing two different amide-based titanium sources, tetrakis-dimethylamido-titanium [(NMe2)4-Ti, TDMAT] and its recently developed derivative, tris-(dimethylamido)-mono-(N,N′-diisopropyl-dimethyl-amido-guanidinato)-titanium {[(N-iPr)2NMe2]Ti(NMe2)3, TiA3G1}, with water vapor as counterreactant. A clear saturation of growth with an increasing precursor supply was found for TDMAT between 150 and 300 °C and for TiA3G1 between 150 and 330 °C. Representative growth per cycle (GPC) values at 250 °C were 0.041 and 0.044 nm/cycle, respectively. Compared to that of TDMAT, ALD of TiA3G1 exhibited a significantly higher stability in the GPC values up to 300 °C coinciding with an improved temperature stability of the precursor. Both processes showed a minimum of the growth rate as a function of temperature. In all cases, the residual carbon and nitrogen contents of the TiO2 films were <3 atom %. Conformal growth was demonstrated on three-dimensional pinhole structures with an aspect ratio of around 1:30. Deposition temperatures of ≤200 °C led to quasi-amorphous films. At higher growth temperatures, the anatase phase developed, accompanied by the brookite and/or the rutile phase depending on process conditions, deposition temperature, and film thickness.

Although all graphites share the same idealized chemical structure, marked differences in fact exist between their reactivities, such as the propensity for oxidation, that need to be taken into consideration for the development of applications. Here we show that five different commercially sourced natural and synthetic graphites differ significantly in their response to a modified Staudenmaier oxidation that produces substoichiometric graphene oxides (sub-GOx). The dominant oxidation product is hydroxyl groups, which can be dehydrate to epoxy groups under mild heating even below 120 °C. The extent of oxidation correlates broadly with the defect band intensity in the starting graphites as measured by Raman spectroscopy. FTIR shows there is a significant concentration of H defects at the % atom level. The results suggest that defects in the graphite plane are more prevalent than previously thought. Finally, the properties of the thermally reduced sub-GOx are also different. The product from the least defective starting graphite ultimately exhibits the lowest activation energies for both electron and hole transport, of the order of 10 μeV below 25 K, that is characteristic of band-like transport. These results are important because they show that the quality of the starting graphite significantly affects the properties of the derived products.

A promising method of synthesizing polymers with useful property relationships utilizes self-assembling lyotropic liquid crystals (LLCs) as photopolymerization templates to direct polymer structure on the nanometer scale. Unfortunately, thermodynamically driven phase separation of the polymer from the LLC template often occurs during polymerization and prevents control over final polymer nanostructure and properties. In this work, the nanostructure of polyacrylamide is controlled through photopolymerization in LLC templates formed using specific concentrations of polymerizable and nonreactive surfactants. Polymer structure information obtained using electron microscopy, X-ray scattering, and polarized light microscopy indicates that LLC nanostructure is retained during photopolymerization at particular reactive surfactant concentrations. Physical properties including water uptake, diffusivity, and mechanical strength are greater in polyacrylamide systems that exhibit nanostructure as compared to isotropic controls of the same chemical composition. Useful property relationships typically unattainable in traditional hydrogel systems are also observed for nanostructured hydrogels including simultaneous increases in water uptake and mechanical strength. These results demonstrate methods of generating and retaining polymer nanostructure during photopolymerization in systems that otherwise phase separate from the LLC template and may be utilized to synthesize nanostructured polymers with property relationships useful in a growing number of advanced applications.

Five new lithium chalcogenidotetrelates, so-called “LiChT” phases, with the elemental combination Li/Sn/Se, Li4[SnSe4] (1), 1∞{Li2[SnSe3]} (2), and the respective solvates Li4[SnSe4]·13H2O (3), Li4[Sn2Se6]·14H2O (4), and Li4[SnSe4]·16MeOH (5) were generated in single-crystalline form. We present and discuss syntheses, crystal structures, spectroscopic and thermal behavior, as well as Li+ ion conducting properties of the phases that represent uncommon Li+ ion conducting materials with a maximum conductivity found for 1 (σ20°C = 2 × 10–5 S·cm–1, σ100°C = 9 × 10–4 S·cm–1). The latter was elucidated via impedance spectroscopy and further studied by electronic structure calculations, revealing vacancy migration as the dominant Li+ transport mechanism. Thus, studies on a selenido-LISICON family were found to be a very interesting starting point for an extension of the LISICON-related solid state lithium ion conductors (SSLIC).

The oxygen nonstoichiometry of mixed conducting perovskite-structured BaxSr1–xTi1–yFeyO3–y/2+δ (BSTF) (x = 0, 0.1, 0.5 and y = 0.05, 0.35) was measured by means of thermogravimetry as a function of oxygen partial pressure, pO2, in a temperature range typical for solid oxide fuel cell (SOFC) cathode applications. With increasing Ba content, the nonstoichiometry curve was shifted to higher pO2, indicating enhanced reducibility. Based on a defect chemical analysis of thermogravimetry derived nonstoichiometry data, the substitution of Ba for Sr on the A-site of STF was found to result in a decrease in both the reduction enthalpy and band gap energy, consistent with expectations that substitution of Sr by the larger Ba leads to a reduction in bond strength. A consequent increase in minority electron density and oxygen vacancy concentration are expected to result in enhancements in oxygen surface exchange kinetics and diffusivity and thereby cathode performance. The nonstoichiometry data obtained in this study also brought to light a previous underestimation of the minority electron density, by approximately a factor of 103, a key parameter believed to impact cathodic performance.

CdSe/CdS/ZnS quantum dots (QDs) have been successfully encapsulated into poly(ethylene oxide) (PEO)-based polymeric micelle/silica dual layers via interfacial templating condensation. The encapsulation follows a green and straightforward microemulsion mechanism that directly proceeds in a near-neutral pH aqueous environment. No detriment to the optical properties of QDs is observed during encapsulation. The core–shell nanoparticles generated possess a polymeric micelle framework with a single QD encapsulated in the hydrophobic micellar core, an ultrathin (<5 nm in thickness) yet robust silica shell confined to the micellar core/corona interface and free PEO chains dangling on the surface. The free PEO chains effectively prevent nonspecific adsorption of biomolecules to the nanoparticles. Double shielding of polymeric micelle/silica shell remarkably improves the fluorescence resistance of QDs to strong acids and highly salted buffers. In vitro testing using MDA-MB-231 breast cancer cells demonstrates that these organic/inorganic dual layer-protected QDs conjugated with folate show noncytotoxicity and bright fluorescence cellular imaging with high target specificity.

Following our recent work on the use of Co(III) complexes as p-type dopants for triarylamine-based organic hole-conductors, we herein report on two new Co(III) complexes for doping applications. With the aim of ameliorating the dopant’s suitability for its use in solid-state dye-sensitized solar cells, we show how the properties of the dopant can be easily adjusted by a slight modification of the molecular structure. We prove the eligibility of the two new dopants by characterizing their optical and electrochemical properties and give evidence that both of them can be used to oxidize the molecular hole-transporter spiro-MeOTAD. Finally, we fabricate high-performance solid-state dye-sensitized solar cells using a state-of-the-art metal-free organic sensitizer in order to elucidate the influence of the type of dopant on device performance.

Group I–III–VI ternary chalcogenides have attracted extensive attention as important functional semiconductors. Among them, Cu–In–S compounds have seen strong research interest due to their potential applications in high-efficiency solar cells. However, the controllable synthesis of Cu–In–S nanostructures with different phases is always difficult. In this research, zinc-blende CuInS2, wurtzite CuInS2, and spinel CuIn5S8 could be selectively synthesized using spinel In3–xS4 as the precursor by a simple solvothermal method. X-ray powder diffraction was used to determine the phase and crystal structure, and transmission electron microscopy was employed to characterize the morphologies of the as-prepared samples. Experiments showed that the acidity–basicity of the reaction system and the coordination and reducibility of the capping ligands were crucial to the final phases of the products. The UV–vis–NIR spectra of the three phases all exhibited a broad-band absorption over the entire visible light and extending into the near-infrared region, and the zinc-blende, wurtzite, and spinel Cu–In–S nanocrystals showed band gaps of 1.55, 1.54, and 1.51 eV, respectively, which indicates their potential applications in thin-film solar cells.

We employed multiwavelength anomalous X-ray dispersion to determine the relative cation occupation at two crystallographically distinct metal sites in Fe2+-, Cu2+-, and Zn2+-exchanged versions of the microporous metal–organic framework (MOF) known as MnMnBTT (BTT = 1,3,5-benzenetristetrazolate). By exploiting the dispersive differences between Mn, Fe, Cu, and Zn, the extent and location of cation exchange were determined from single crystal X-ray diffraction data sets collected near the K edges of Mn2+ and of the substituting metal, and at a wavelength remote from either edge as a reference. Comparing the anomalous dispersion between these measurements indicated that the extent of Mn2+ replacement depends on the identity of the substituting metal. We contrasted two unique methods to analyze this data with a conventional approach and evaluated their limitations with emphasis on the general application of this method to other heterometallic MOFs, where site-specific metal identification is fundamental to tuning catalytic and physical properties.

In this contribution, we present the formation of mesoporous polyampholyte networks via self-complexation (inter- and intrapolyelectrolyte complexation) of copolymers bearing both the imidazolium cations and the carboxylic acid units. The copolymers were prepared via straightforward free radical copolymerization of acrylic acid and vinylimidazolium-based ionic liquid monomers possessing different alkyl substituents in DMSO at 80 °C. Nitrogen adsorption measurements and electron microscopy were used to examine the porous structures. The Brunauer–Emmett–Teller (BET) specific surface areas of the resulting mesoporous complexes were measured to be up to 260 m2/g and varied in terms of the complexation solvent quality, the copolymer composition, and the precipitation concentration of copolymers as well as the chemical structure of the employed ionic liquid monomers. The CO2 sorption behavior of a selected mesoporous polyampholyte was studied in detail. It could be shown that two processes are effective: adsorption at the external surface and absorption into the polymer matrix. Fourier transform infrared (FTIR) spectroscopy gave hints that the absorption process comes along with the formation of imidazolium-carboxylates, presumably via a transient N-heterocyclic carbene intermediate.

Incorporating mixed oxygen-ion-electron conducting (MIEC) cathode materials is a promising strategy to make intermediate-temperature solid oxide fuel cells (IT-SOFCs) viable; however, a lack of fundamental understanding of oxygen transport in these materials limits their development. Density functional theory plus U (DFT+U) calculations are used to investigate how the Sr concentration affects the processes that govern oxygen ion transport in La1-xSrxFeO3-δ (LSF, x = 0, 0.25, and 0.50). Specifically, we show that oxygen vacancies compensate holes introduced by Sr and that this compensation facilitates oxygen vacancy formation in LSF. We also find that oxygen migration in LaFeO3 is accompanied by electron transfer in the opposite direction. Our results explicitly identify and clarify the role of electron-deficient substitutions in promoting oxygen diffusion in LSF. This atomic level insight is important for enabling rational design of iron-based SOFC cathode materials.

The tavorite polymorph of LiFeSO4F has recently attracted a lot of interest as a cathode material for lithium ion batteries stimulated by its competitive specific capacity, high potential for the Fe2+/Fe3+ redox couple, and low-temperature synthesis. However, the synthesis routes explored to date have resulted in notably varied electrochemical performance. This inconsistency is difficult to understand given the excellent purity, crystallinity, and similar morphologies achieved via all known methods. In this work, we examine the role of the interfacial chemistry on the electrochemical functionality of LiFeSO4F. We demonstrate that particularly poor electrochemical performance may be obtained for pristine materials synthesized in tetraethylene glycol (TEG), which represents one of the most economically viable production methods. By careful surface characterization, we show that this restricted performance can be largely attributed to residual traces of TEG remaining on the surface of pristine materials, inhibiting the electrochemical reactions. Moreover, we show that optimized cycling performance of LiFeSO4F can be achieved by removing the unwanted residues and applying a conducting polymer coating, which increases the electronic contact area between the electrode components and creates a highly percolating network for efficient electron transport throughout the composite material. This coating is produced using a simple and scalable method designed to intrinsically favor the functionality of the final product.

In this work, we have successfully developed a novel multifunctional near-infrared (NIR)-stimulus controlled drug release system based on gold nanocages as photothermal cores, mesoporous silica shells as supporters to increase the anticancer drug loading and thermally responsive poly(N-isopropylacrylamide) (PNIPAM) as NIR-stimuli gatekeepers (Au-nanocage@mSiO2@ PNIPAM). The unique Au-nanocage@mSiO2 nanocarrier was elaborately fabricated by utilizing yolk-shell Ag-nanocube@mSiO2 nanostructure as a template by means of spatially confined galvanic replacement. The Au nanocage cores can effectively absorb and convert light to heat upon irradiation with a NIR laser, resulting in the collapse of the PNIPAM shell covering the exterior of mesoporous silica, and exposes the pores of mesoporous silica shell, realizing the triggered release of entrapped DOX drugs. The in vitro studies have clearly demonstrated the feasibility and advantage of the novel nanocarriers for remote-controlled drug release systems.

The efficiency roll-off characteristics in highly efficient thermally activated delayed fluorescence (TADF) based organic light-emitting diodes (OLEDs) were effectively suppressed by controlling the molecular orientation of a 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host matrix. The hole mobility in the light emitting layer was found to govern the magnitude of this suppression. Three-dimensional finite-difference time-domain calculations and photoluminescence quantum yield measurements revealed that the optical characteristics of the fabricated devices and photophysical properties of the TADF emitter did not affect efficiency roll-off. CBP molecules adopted random orientations when films were fabricated at high temperature (350 K), resulting in low hole mobility, and shifting the recombination zone away from the interface of the emitting layer with the electron transporting layer. When CBP was randomly orientated, efficiency roll-off was suppressed by 30% at a current density of 100 mA cm–2. This result indicates that control of the molecular orientation of the host can allow us to indirectly tune the carrier balance in OLEDs.

In this work, we investigated the effect of Rb and Ta doping on the ionic conductivity and stability of the garnet Li7+2x–y(La3–xRbx)(Zr2–yTay)O12 (0 ≤ x ≤ 0.375, 0 ≤ y ≤ 1) superionic conductor using first principles calculations. Our results indicate that doping does not greatly alter the topology of the migration pathway, but instead acts primarily to change the lithium concentration. The structure with the lowest activation energy and highest room temperature conductivity is Li6.75La3Zr1.75Ta0.25O12 (Ea = 19 meV, σ300K = 1 × 10–2 S cm–1). All Ta-doped structures have significantly higher ionic conductivity than the undoped cubic Li7La3Zr2O12 (c-LLZO, Ea = 24 meV, σ300K = 2 × 10–3 S cm–1). The Rb-doped structure with composition Li7.25La2.875Rb0.125Zr2O12 has a lower activation energy than c-LLZO, but further Rb doping leads to a dramatic decrease in performance. We also examined the effect of changing the lattice parameter at fixed lithium concentration and found that a decrease in the lattice parameter leads to a rapid decline in Li+ conductivity, whereas an expanded lattice offers only marginal improvement. This result suggests that doping with larger cations will not provide a significant enhancement in performance. Our results find higher conductivity and lower activation energy than is typically reported in the experimental literature, which suggests that there is room for improving the total conductivity in these promising materials.

The highly ionic, high refractive index La2O3–Nb2O5 system has a La-rich glass forming region and another Nb-rich glass forming region. The La-rich and Nb-rich regions have markedly different structural and physical properties. Structural analyses using diffraction and spectroscopic measurements combined with structural modeling show that the Nb-rich glass, which has unusually high oxygen packing density, is a network of distorted NbOn polyhedra with mainly corner-sharing, and LaOx polyhedra with both corner-sharing and edge-sharing. Contrastingly, in the La-rich glass, small-sized symmetrical NbOn polyhedra with a large amount of edge-sharing are inhomogenously distributed in the network of LaOx polyhedra. The drastic connectivity change of cation–oxygen polyhedra and the dense oxygen packing due to edge-sharing polyhedra contravene long-established rules of oxide glass formation. These results raise the possibility that novel higher refractive index with lower wavelength dispersion glasses, which contain highly ionic heavy elements at the lower left in the periodic table, may be synthesized.

At high pressures, spinel compounds can transform to CaFe2O4, CaMn2O4, or CaTi2O4 phases, which are regarded as post-spinel phases. Here, first-principles calculations are used to systematically study the stability of post-spinel LiMn2O4, NaMn2O4, and MgMn2O4, as well as their potential application as rechargeable battery cathodes. Thermodynamically, the stability of the post-spinel phase is highly related to the electronic configuration of transition-metal ions. By changing the concentration of Jahn–Teller active Mn3+, the relative stabilities of post-spinel phases can be easily monitored. It provides a practical way to obtain post-spinel compounds with desirable structures. Kinetically, post-spinel phases can be stable under ambient conditions, because of the high barrier that must be overcome to rearrange MnO6 octahedrons. The most spectacular finding in this work is the high cationic mobility in post-spinel compounds. The activation energy barrier of the migration of Mg2+ in CaFe2O4-type MgMn2O4 is 0.4 eV, suggesting that the mobility of Mg2+ in this compound is comparable to that of Li+ in typical Li-ion battery cathodes. To explore the potential application of post-spinel compounds as rechargeable battery cathodes, the voltage profile for the electrochemical insertion/removal of Mg in CaFe2O4-type MgMn2O4 is predicted. Its theoretical energy density is 1.3 times greater than that of typical Li-ion battery cathodes. These outstanding properties make CaFe2O4-type MgMn2O4 an attractive cathode candidate for rechargeable Mg batteries.

Carbon-supported La1–xCaxMn1–yFeyO3 nanoparticles were synthesized, and their oxygen reduction activities and electronic states were investigated. A reverse micelle method using KMnO4 as a source of high valence state Mn successfully yielded carbon-supported La1–xCaxMn1–yFeyO3 nanoparticles even when calcined under a reducing atmosphere. The oxygen reduction activity of carbon-supported La1–xCaxMn1–yFeyO3 exceeded that of carbon-supported Pt nanoparticles when the Ca composition was limited to the range of 0.4 to 0.8. X-ray photoelectron spectroscopy (XPS) measurements of La1–xCaxMn1–yFeyO3 particle surfaces revealed the existence of Mn4+, which is important in the oxygen reduction activity. Depth analysis of La1–xCaxMn1–yFeyO3 nanoparticles by XPS revealed the formation of a CaCO3 impurity and an A-site deficient perovskite-type oxide containing a high surface concentration of Mn4+.

We report a detailed study of the dynamics of oxide ionic conduction in brownmillerite-type Sr2Fe2O5, including lattice anisotropy, based on neutron scattering studies of a large (partially twinned) single crystal in combination with ab initio molecular dynamics simulations. Single-crystal diffraction reveals supercell peaks due to long-range ordering among chains of corner-sharing FeO4 tetrahedra, which disappears on heating above 540 °C due to confined local rotations of tetrahedra. Our simulations show that these rotations are essentially isotropic, but are a precondition for the anisotropic motion that moves oxide ions into the tetrahedral layers from the octahedral layers, which we observe experimentally as a Lorentzian broadening of the quasielastic neutron scattering spectrum. This continual but incoherent movement of oxide ions in turn creates conduction pathways and activates long-range diffusion at the interface between layers, which appears to be largely isotropic in two dimensions, in contrast with previously proposed mechanisms that suggest diffusion occurs preferentially along the c axis.

[Zr(NEtMe)2(guan-NEtMe2)2], a recently developed compound, was investigated as a novel precursor for the atomic layer deposition (ALD) of ZrO2. With water as the oxygen source, the growth rate remained constant over a wide temperature range, whereas with ozone the growth rate increased steadily with deposition temperature. Both ALD processes were successfully developed: the characteristic self-limiting ALD growth mode was confirmed at 300 °C. The growth rates were exceptionally high, 0.9 and 1.15 Å/cycle with water and ozone, respectively. X-ray diffraction (XRD) indicated that the films were deposited in the high-permittivity cubic phase, even when grown at temperatures as low as 250 °C. Compositional analysis performed by means of X-ray photoelectron spectroscopy (XPS) demonstrated low carbon and nitrogen contamination (<2 at. % when deposited with ozone). The films presented low root-mean-square (rms) roughness, below 5% of the film thickness, as well as excellent step coverage and conformality on 30:1 aspect ratio trench structures. Dielectric characterization was performed on ZrO2 metal–insulator–metal (MIM) capacitors and demonstrated high permittivity and low leakage current, as well as good stability of the capacitance. The ALD reaction mechanism was studied in situ: adsorption of the precursor through reaction of the two guan-NEtMe2 ligands with the surface −OD groups was confirmed by the quartz crystal microbalance (QCM) and quadrupole mass spectrometric (QMS) results.

The synthesis of Ge nanowires with very high-aspect ratios (greater than 1000) and uniform crystal growth directions is highly desirable, not only for investigating the fundamental properties of nanoscale materials but also for fabricating integrated functional nanodevices. In this article, we present a unique approach for manipulating the supersaturation, and thus the growth kinetics, of Ge nanowires using Au/Ge bilayer films. Ge nanowires were synthesized on substrates consisting of two parts: a Au film on one-half of a Si substrate and a Au/Ge bilayer film on the other half of the substrate. Upon annealing the substrate, Au and Au/Ge binary alloy catalysts were formed on both the Au and Au/Ge-sides of the substrates, respectively, under identical conditions. The mean lengths of Ge nanowires produced were found to be significantly longer on the Au/Ge bilayer side of the substrate compared to the Au-coated side, as a result of a reduced incubation time for nucleation on the bilayer side. The mean length and growth rate on the bilayer side (with a 1 nm Ge film) was found to be 5.5 ± 2.3 μm and 3.7 × 10–3 μm s–1, respectively, and 2.7 ± 0.8 μm and 1.8 × 10–3 μm s–1 for the Au film. Additionally, the lengths and growth rates of the nanowires further increased as the thickness of the Ge layer in the Au/Ge bilayer was increased. In-situ TEM experiments were performed to probe the kinetics of Ge nanowire growth from the Au/Ge bilayer substrates. Diffraction contrast during in situ heating of the bilayer films clarified the fact that thinner Ge films, that is, lower Ge concentration, take longer to alloy with Au than thicker films. Phase separation was also more significant for thicker Ge films upon cooling. The use of binary alloy catalyst particles, instead of the more commonly used elementary metal catalyst, enabled the supersaturation of Ge during nanowire growth to be readily tailored, offering a unique approach to producing very long high aspect ratio nanowires.

The layer-by-layer formation of core/alloy nanoparticles is described. Using presynthesized gold nanoparticle cores, AuxAg1-x alloy shells were deposited and annealed with subnanometer precision using a microwave irradiation (MWI) mediated hydrothermal processing method. The alloy composition, thickness, and nanoparticle morphology governed the surface plasmon resonance characteristics of the particles, as well as growth characteristics. The mechanism for alloy deposition, annealing, and interdiffusion was explored using two gold precursors, [AuBr4]− and [AuCl4]−, and two hydrothermal temperatures (120, 160 °C). Findings indicate that use of [AuCl4]− results in significant galvanic displacement, leading to nonuniform alloy formation and phase segregation at low annealing temperatures, which leads to loss of morphology control at intermediate compositions (x ≈ 0.25–0.75). In contrast, use of [AuBr4]− results in alloy shells with low galvanic interactions, leading to optimum alloy distribution and high fidelity control of alloy-shell thickness that, in combination with higher hydrothermal processing temperatures, leads to uniform and monodisperse core/alloy microstructure across all compositions. The alloy deposition and core/alloy nanoparticle growth was followed in situ by monitoring the change in surface plasmon resonance (SPR) signatures by UV–vis, which were unique to alloy shell thickness, as well as composition, and morphology. The interfacial alloy composition was probed by modeling the SPR with discrete dipole approximation, the results of which suggest the final alloy shells are Au-rich compared to the feed ratios, owing in large part to both galvanic displacements as well as core-to-shell alloy interdiffusion.

The origin of the almost unique combination of optical transparency and the ability to bipolar dope tin monoxide is explained using a combination of soft and hard X-ray photoemission spectroscopy, O K-edge X-ray emission and absorption spectroscopy, and density functional theory calculations incorporating van der Waals corrections. We reveal that the origin of the high hole mobility, bipolar ability, and transparency is a result of (i) significant Sn 5s character at the valence band maximum (due to O 2p–Sn 5s antibonding character associated with the lone pair distortion), (ii) the combination of a small indirect band gap of ∼0.7 eV (Γ–M) and a much larger direct band gap of 2.6–2.7 eV, and (iii) the location of both band edges with respect to the vacuum level. This work supports Sn2+-based oxides as a paradigm for next-generation transparent semiconducting oxides.

A series of bimetallic carbides of the form β-(Mo1–xVx)2C (0 < x < 0.12) was synthesized by carbothermal reduction of corresponding h-Mo1–xVxO3 precursors. The oxides were synthesized by precipitation, and the subsequent carbide phase development was monitored. The reduction mechanism is discussed on the basis of observed structural evolution and solid-state kinetic data. The reduction is observed to proceed via a complex mechanism involving the initial formation of defective MoIV oxide. Increasing the V content retards the onset of reduction and strongly influences the kinetics of carburization. The carbides exhibit a trend in the growth morphology with V concentration, from a particulate-agglomerate material to a packed, nanofibrous morphology. The high-aspect-ratio crystallites exhibit pseudomorphism, and in the case of the V-containing materials, some preferential crystal orientation of grains is observed. An increasing mesoporosity is associated with the fibrous morphology, as well as an exceptionally high surface area (80–110 m2/g). The synthesis was subsequently scaled up. By adapting the heating rate, gas flow, and pretreatment conditions, it was possible to produce carbide materials with comparable physical properties to those obtained from the small scale. As a result, it was possible to synthesize Mo2C materials in multigram quantities (5–15 g) with BET surface areas ranging from 50 to 100 m2/g, among the highest values reported in the literature.

Osmotic swelling and exfoliation behaviors in a lepidocrocite-type titanate H1.07Ti1.73O4·H2O were investigated upon reactions with tetramethylammonium (TMA+) and tetrabutylammonium (TBA+) cations. The reaction products in various physical states (suspension, wet aggregate, and deposited nanosheets) were characterized by several techniques, including X-ray diffraction under controlled humidity, small-angle X-ray scattering, particle size analysis, and atomic force microscopy. As the ratio of tetraalkylammonium ion in a solution to exchangeable proton in a solid decreased, the predominant product changed from the osmotically swollen phase, having an interlayer spacing d of several tens of nanometers, to the exfoliated nanosheets. The different behaviors of two cations in the osmotic swelling were evident from the slope and the transition point in the d versus C–1/2 plot, where C is the concentration of the cations. At a short reaction time, crystallites of a few stacks were obtained as a major product in the reaction with TMA+. On the other hand, a mixture of those crystallites and a significant portion of unilamellar nanosheets were obtained in the reaction with TBA+. In both cases, those stacks were ultimately thinned down at long reaction time to unilamellar nanosheets. The lateral size of the nanosheets could be controlled, depending on the type of the cations, the tetraalkylammonium-to-proton ratios, and the mode of the reaction (manual versus mechanical shaking). The nanosheets produced by TMA+ had large lateral sizes up to tens of micrometers, and the suspension showed a distinctive silky appearance based on liquid crystallinity. Our work provides insights into the fundamentals of osmotic swelling and exfoliation, allowing a better understanding of the preparation of nanosheets, which are one of the most important building blocks in nanoarchitectonics.

Two nonlinear optical fluoride carbonate crystals (Na8Lu2(CO3)6F2 and Na3Lu(CO3)2F2) have been synthesized under subcritical hydrothermal condition. Both crystals crystallize in the noncentrosymmetric space group Cc (No. 9). The structure of Na8Lu2(CO3)6F2 with high density of [CO3] groups is described as 1D [Na5Lu(CO3)2F2] chains connected by [CO3] triangles, forming an intricate three-dimensional framework. Lu3+ and Na+ cations are alternatively ordered and disordered in the cavities of the 3D network. The structure of Na3Lu(CO3)2F2 is built up from the [NaLu(CO3)2F2] layers which are separated by other Na+ cations. The [CO3] anionic groups arrange approximately coparallel to the plane. The second harmonic generation (SHG) measurement indicates that Na8Lu2(CO3)6F2 and Na3Lu(CO3)2F2 have large SHG responses that are approximately 4.29 and 4.21 times KH2PO4 (KDP), respectively. The responses are also phase-matchable in the visible region. In addition, it exhibits wide transparent regions ranging from UV to near IR with a short UV cutoff edge (<200 nm), which suggests that the new compounds are promising as deep-UV NLO materials.

In a study combining high-resolution single-crystal neutron diffraction and solid-state nuclear magnetic resonance, the mixed ionic-electronic conductor γ-Ba4Nb2O9 is shown to have a unique structure type, incorporating niobium in 4-, 5-, and 6-coordinate environments. The 4- and 5-coordinate niobium tetrahedra and trigonal bipyrimids exist in discrete layers, within and among which their orientations vary systematically to form a complex superstructure. Through analysis and comparison of data obtained from hydrated versus dehydrated samples, a mechanism is proposed for the ready hydration of the material by atmospheric water. This mechanism, and the resulting hydrated structure, help explain the high protonic and oxide ionic conductivity of γ-Ba4Nb2O9.

Cu2ZnSnS4 (CZTS) is a promising material for thin film solar cells based on sustainable resources. This paper explores some consequences of the chemical instability between CZTS and the standard Mo “back contact” layer used in the solar cell. Chemical passivation of the back contact interface using titanium nitride (TiN) diffusion barriers, combined with variations in the CZTS annealing process, enables us to isolate the effects of back contact chemistry on the electrical properties of the CZTS layer that result from the synthesis, as determined by measurements on completed solar cells. It is found that instability in the back contact is responsible for large current losses in the finished solar cell, which can be distinguished from other losses that arise from instabilities in the surface of the CZTS layer during annealing. The TiN-passivated back contact is an effective barrier to sulfur atoms and therefore prevents reactions between CZTS and Mo. However, it also results in a high series resistance and thus a reduced fill factor in the solar cell. The need for high chalcogen pressure during CZTS annealing can be linked to suppression of the back contact reactions and could potentially be avoided if better inert back contacts were to be developed.

We have recently developed a colloidal route to vanadium sesquioxide (V2O3) nanocrystals with a metastable bixbyite crystal structure. In addition to being one of the first reported observations of the bixbyite phase in V2O3, it is also one of the first successful colloidal syntheses of any of the vanadium oxides. The nanocrystals, measuring 5 to 30 nm in diameter, possess a flower-like morphology which densify into a more spherical shape as the reaction temperature is increased. The bixbyite structure was examined by X-ray diffraction and an aminolysis reaction pathway was determined by Fourier transform infrared spectroscopy. A direct band gap of 1.29 eV was calculated from optical data. Under ambient conditions, the structure was found to expand and become less distorted, as evidenced by XRD. This is thought to be due to the filling of structural oxygen vacancies in the bixbyite lattice. The onset of the irreversible transformation to the thermodynamically stable rhombohedral phase of V2O3 occurred just under 500 °C in an inert atmosphere, accompanied by slight particle coarsening. A critical size of transformation between 27 and 42 nm was estimated by applying the Scherrer formula to analyze XRD peak widths during the course of the transformation. The slow kinetics of transformation and large critical size reveal the remarkable stability of the bixbyite phase over the rhombohedral phase in our nanocrystal system.

We report a phosphine-free colloidal synthesis of CuInxGa1–xS2 (CIGS) nanocrystals (NCs) by heating a mixture of metal salts, elemental sulfur, octadecene, and oleylamine. In contrast with the more commonly used hot injection, this procedure is highly suitable for large-scale NC production, which we tested by performing a gram-scale synthesis. The composition of the CIGS NCs could be tuned by varying the In and Ga precursor ratios, and the samples showed a composition-dependent band gap energy. The average particle size was scaled from 13 to 19 nm by increasing the reaction temperature from 230 to 270 °C. Two concomitant growth mechanisms took place: in one, covellite (CuS) NCs nucleated already at room temperature and then incorporated increasing amounts of In and Ga until they evolved into chalcopyrite CIGS NCs. In the second mechanism, CIGS NCs directly nucleated at intermediate temperatures. They were smaller than the NCs formed by the first mechanism, but richer in In and Ga. In the final sample, obtained by prolonged heating at 230–270 °C, all NCs were homogeneous in size and composition. Attempts to replace the native ligands on the surface of the NCs with sulfur ions (following literature procedures) resulted in only around 50% exchange. Films prepared using the partially ligand exchanged NCs exhibited good homogeneity and an ohmic dark conductivity and photoconductivity with a resistivity of about 50 Ω·cm.

Selenium substitution on a ladder-type indacenodithiophene-based polymer (PIDT-DFBT) is investigated in order to reduce band gap, improve charge mobilities, and enhance the photovoltaic performance of the material. The new indacenodiselenophene-based polymer (PIDSe-DFBT) possessed improved absorption over its sulfur analogue in films, as well as substantially higher charge mobilities (0.15 and 0.064 cm2/(V s) hole and electron mobility, respectively, compared to 0.002 and 0.008 cm2/(V s) for PIDT-DFBT). The enhanced material properties led to an improved power conversion efficiency of 6.8% in photovoltaic cells, a 13% improvement over PIDT-DFBT-based devices. Furthermore, we examined the effect of molecular weight on the properties of PIDSe-DFBT and found not only a strong molecular weight dependence on mobilities, but also on the absorptivity of polymer films, with each 15 000 g/mol increase in weight, leading to a 25% increase in the absorptivity of the material. The molecular weight dependence of the material’s properties resulted in a significant difference in photovoltaic performance with the high-molecular-weight PIDSe-DFBT providing a higher photocurrent, fill factor, and efficiency due to its improved absorption and hole mobility. These results demonstrate the importance of achieving high molecular weight and the potential that selenium-containing ladder-type polymers have in the design of high-performance semiconducting polymers for organic photovoltaics (OPVs).

Rational design and synthesis of polymeric semiconductors is critical to the development of polymer solar cells (PSCs). In this work, a new series of benzodithiophene–difuranylbenzooxadiazole-based donor–acceptor co-polymers—namely, PBDT-DFBO, PBDTT-DFBO, and PBDTF-DFBO, with various side groups—have been developed for bulk-heterojunction PSCs. These side-group substituents provide the opportunity to tailor the opto-electrical properties of the polymers. In addition, we show that the reduction of the bandgap of polymers and the enhancement of charge mobility in the devices can be accomplished concurrently by substituting the alkylthienyl side group with its furan counterpart. In the preliminary investigation, one could obtain PSCs with a power conversion efficiency (PCE) of 2.1% for PBDT-DFBO with an alkoxyl side chain, 2.2% for PBDTT-DFBO with an alkylthienyl side group, and 3.0% for PBDTF-DFBO with an alkylfuranyl side group. Further optimizing the performance of the devices was conducted via a simple solvent treatment. The PSCs based on PBDTF-DFBO:PC71BM could even achieve 7.0% PCE, which exhibited an enhancement of 130%. To the best of our knowledge, the value of 7.0% is the highest efficiency for furan-containing PSCs to date and is also comparable with the hitherto reported highest efficiency of the single junction PSCs. Through a combination of testing charge transport by the space-charge limited current (SCLC) model and examining the morphology by atomic force microscopy (AFM), we found that the effects of solvent treatment on the improved performance originate from higher and more balanced charge transport and the formation of fiberlike interpenetrating morphologies, which are beneficial to the increase of short-circuit current density (Jsc) and fill factor (FF). This work demonstrates a good example for tuning absorption range, energy level, charge transport, and photovoltaic properties of the polymers by side-chain engineering and the solvent treatment can offer a simple and effective method to improve the efficiency of PSCs.

A large array of easily available small-molecule (as opposed to industrial oligomeric) triisocyanates and aromatic polyols render polyurethanes a suitable model system for a trend-based systematic study of structure–property relationships in nanoporous matter as a function of the monomer structure. Molecular parameters of interest include rigidity, number of functional groups per monomer (n), and functional group density (number of functional groups per phenyl ring, r). All systems were characterized from gelation to the bulk properties of the final aerogels. Molecular and nanoscopic features of interest, including skeletal composition, porous structure, nanoparticle size, and assembly, were probed with a combination of liquid- and solid-state 13C and 15N NMR, rheometry, N2- and Hg-porosimetry, SEM, and small-angle X-ray scattering (SAXS). Macroscopic properties such as styrofoam-like thermal conductivities (∼0.030 W m–1K–1), foam-like flexibility, or armor-grade energy absorption under compression (up to 100 J g–1) were correlated with one another and serve as a top-down probe of the interparticle connectivity, which was again related to the monomer structure. Overall, both molecular rigidity and multifunctionality control phase-separation, hence, particle size and by association porosity (e.g., meso versus macro) and internal surface area. With sufficiently rigid monomers, skeletal frameworks include intrinsic microporosity, rendering the resulting materials hierarchically nanoporous over the entire porosity regime (micro to meso to macro). Most importantly, however, clear roles have been identified not only for the absolute number of functional groups per monomer, but also for parameter r. The latter is expressed onto the surface of the skeletal nanoparticles (controls the surface functional group density per unit mass) and becomes the dominant structure-directing as well as property-determining parameter. By relating the molecular functional group density with the functional group density on the nanoparticle surfaces, these results establish that for three-dimensional (3D) assemblies of nanoparticles to form rigid nanoporous frameworks, they have first and foremost to be able to develop strong covalent bonding with one another. These findings are relevant to the rational design of 3D nanostructured matter, not limited to organic aerogels.

High temperature rocksalt phases of AgBiS2 and AgBiS2-xSex (x = 0.05–0.1) have been kinetically stabilized at room temperature in nanocrytals (∼11 nm) by simple solution-based synthesis. Experimental evidence for this derives from variable temperature powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electron diffraction analysis. The band gap of the AgBiS2 nanocrystals (∼1.0 eV) is blue-shifted by quantum confinement relative to that of the cubic bulk phase of AgBiS2. Moreover, systematic lower energy shift of the band gap in AgBiS2-xSex nanocrystals compared to pristine nanocrystalline AgBiS2 was observed with increasing Se concentration. Existence of fascinating order–disorder type transition in these nanocrystals was evidenced by temperature dependent electrical conductivity, thermopower, and heat capacity measurements. Disordered cation sublattice and nanoscale grain boundaries coupled with strong Bi–S bond anharmonicity allow effective phonon scattering, which leads to minimal lattice thermal conductivity of the nanocrystalline AgBiS2.

The recent synthesis of single-layer GaS and GaSe opens the question of stability for other single-layer group-III monochalcogenides (MX, M = Ga and In, X = S, Se, and Te) and how the dimension reduction affects the properties of these materials. Using a first-principles design approach, we determine that the single-layer group-III monochalcogenides exhibit low formation energies and are suitable for photocatalytic water splitting. First, density-functional calculations using a van der Waals functional reveal that the monochalcogenides have formation energies similar to that of single-layer MoS2, implying the ease of mechanically extracting single-layer monochalcogenides from their layered bulk counterparts. Next, calculations using a hybrid density functional and the quasiparticle many-body G0W0 approximation determine the conduction and valence band edge positions. Comparing the band edge positions with the redox potentials of water shows that single-layer monochalcogenides are potential photocatalysts for water splitting. Moreover, the bandgaps, band edge positions, and optical absorption of the single-layer monochalcogenides can be tuned by biaxial strain to increase the efficiency of solar energy conversion. Finally, calculations of the enthalpy of solvation of the single-layer monochalcogenides suggest their stability in aqueous solution.

Phenylboronic acids (PBAs) are being considered for glucose sensing and controlled insulin release, because of their affinity for diol-containing molecules. The interaction of immobilized PBAs in a hydrogel matrix with glucose can lead to volumetric changes that have been used to monitor glucose concentration and release insulin. Although the interaction of PBAs with diol-containing molecules has been intensively studied, the response of PBA-modified hydrogels as a function of the specific PBA chemistry is not well understood. To understand the interaction of immobilized PBAs with glucose in hydrogel systems under physiological conditions, the glucose-dependent volumetric changes of a series of hydrogel sensors functionalized with different classes of PBAs were investigated. The volume change induced by PBA-glucose interactions is converted to the diffracted wavelength shift by a crystalline colloidal array embedded in the hydrogel matrix. The PBAs studied contain varying structural parameters such as the position of the boronic acid on the phenyl ring, different substituents on PBAs and different linkers to the hydrogel backbone. The volumetric change of the PBA modified hydrogels is found to be highly dependent on the chemical structure of the immobilized PBAs. The PBAs that appear to provide linear volumetric responses to glucose are found to also have slow response kinetics and significant hysteresis, while PBAs that show nonlinear responses have fast response kinetics and small hysteresis. Electron-withdrawing substituents, which reduce the pKa of PBAs, either increase or decrease the magnitude of response, depending on the exact chemical structure. The response rate is increased by PBAs with electron-withdrawing substituents. Addition of a methylene bridge between the PBA and hydrogel backbone leads to a significant decrease in the response magnitude. PBAs with specific desirable features can be selected from the pool of available PBAs and other PBA derivatives with desired properties can be designed according to the findings reported here.

A family of naphthalene diimide (NDI)-based donor (D)-acceptor (A) copolymers with various acene- (benzene (Bz), naphthalene (Np), and pyrene (Py)) and heteroacene-type (selenophene (Se) and thiophene (Th)) donor rings has been designed and synthesized as a means to systematically understand structure–property relationships on the subject of the structural factor and electron-donating capability of the donor portions for applications in organic field-effect transistors (OFETs) based on NDIs. Alongside of two categories dealing with the lack or existence of the heteroatoms in the donor framework, the resulting copolymers can also be classified into ‘thiophene-free’ D–A copolymers (PNDI-Bz, PNDI-Np, PNDI-Py, and PNDI-Se) and thiophene-containing copolymer (PNDI-Th). The results from optical and electronic properties lead to the determination that the empirical electron-donating strength of donor co-units is in the order of Bz < Np < Py < Th < Se. In contrast with the similarity of the LUMO levels (−3.73∼−3.82 eV) due to the dominant NDI contribution to the polymer backbone, the HOMO levels are sensitive to the relative electron-donating ability and shown to primarily influence whether unipolar n-channel (PNDI-Bz and PNDI-Np) or ambipolar charge transport (PNDI-Py, PNDI-Se, and PNDI-Th) is observed in OFETs of the NDI-based copolymers. Intriguingly, regardless of the strong electron donors toward efficient intramolecular charge transfer (ICT), the best OFET performance is observed in the acene-based centrosymmetric copolymer PNDI-Np (5.63 × 10–2 cm2 V–1 s–1) when compared to those of the other copolymers with axisymmetric units. Thus, the present work highlights that the geometric features of the donors in NDI D–A copolymers strongly reflect the carrier mobility dynamics rather than inserting electron-rich donor moieties into the backbone to lower the band gap and further strengthen ICT.

Because of the fundamental properties and possible applications in spin-based electronics and photonics, diluted magnetic semiconductor nanowires are actively pursued. Here we report a general and facile solution synthetic strategy to prepare colloidal diluted magnetic semiconductor nanowires through solution-liquid–solid (SLS) doping approach using single-source precursors. On the basis of this strategy, transition metal ions such as Mn and Eu doped CdS nanowires were successfully synthesized and characterized. The material characterizations demonstrated that the doping process is nucleation controlled. We further investigated the Mn doping effects on nanowire growth as well as their photoluminescence properties. The Mn doped CdS nanowires exhibit photoluminescence emission related to the excitonic magnetic polaron in CdS, single Mn2+ ion and Mn–S–Mn centers as well as trap states, evidenced by the time-resolved photoluminescence spectra and magnetic measurements. With the increase of Mn precursor that used in the doping process, the Mn2+ related emission becomes more pronounced. By tuning the doping concentration, white emissive doped CdS nanowires were achieved.

The influence of synthesis temperature and time on the length (capacity) of the plateau region during first charge in the high-capacity lithium-rich layered oxide Li1.2Mn0.6Ni0.2O2 and on the reversible capacity during subsequent charge–discharge cycles has been systematically investigated. The samples were synthesized by firing a sol–gel precursor obtained at 450 °C at various temperatures (850–1000 °C) for 24 h and at the optimum temperature of 900 °C for 6–72 h. The maximum length of the plateau region during the first charge and, consequently the maximum reversible capacity were achieved with the sample fired at 900 °C for 24 h. In contrast, the sample fired at 1000 °C for 24 h does not show any plateau region. In-depth characterization by X-ray diffraction, aberration-corrected transmission electron microscopy, scanning electron microscopy, inductively coupled plasma analysis, and electrochemical charge–discharge measurements reveals that the actual lithium content in the synthesized samples, compositional inhomogeneities, and the presence of a single C2/m phase vs a C2/m + R3̅m two-phase mixture play a critical role in the length of the plateau region, while particle size and surface area play a minor role. The study demonstrates the benefits of the formation of a single-phase C2/m solid solution with a lithium content of at least 1.16 in order to maximize the discharge capacity.