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Herein, a newly developed non-noble metal water splitting catalyst based on NiCuCoS3 was reported. Water splitting catalysts are largely developed with noble-based transition metals to lower the energy requirement for the overall water splitting reactions. However, the high cost of precious metal-based catalyst necessitated ongoing search for cheap and efficient oxygen and hydrogen evolution reaction catalysts. NiCuCoS3 were prepared by solventless solid state method and was well characterized by several techniques including field emission scanning electron microscopy (FESEM), X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared red spectroscopy (FTIR), energy dispersive X-ray spectroscopy (XEDS). The as-prepared NiCuCoS3 was applied for water splitting activities with satisfactory performance. The onset for the oxygen evolution reaction (OER) in 1 M KOH was noticed at the electrode potential E = 1.78 V-/RHE (vs. the reversible hydrogen electrode corresponding to an overpotential eta = 0.55 V, with a current density of 10 mA cm(2) obtained at E = 1.92 V-/RHE (eta = 0.69 V). Similarly, the hydrogen evolution reaction (HER) occurred at an onset of E = 0.58 V-/RHE, with a current density of 10 mA/cm(2) obtained at E = 0.60 V-/RHE (with h equal to E vs. RHE for the HER). Likewise, OER and HER had Tafel slopes (130 mV/dec and 116 mV/dec respectively). The developed catalyst also showed high stability as established by linear sweep voltammetry, chronoamperometry and chronopotentiometry. This approach is seen as the right track of making water electrolysis for hydrogen energy feasible through provision of low-energy requirement for electrolytic process. (C) 2021 The Author(s). Published by Elsevier B.V.

Lattice-strained Bi2S3 with 3D hierarchical structures are prepared through a top-down route by a topotactic transformation. High-resolution transmission electron microscopy and X-ray diffraction (XRD) confirm the lattice spacing is expanded by prolonged sulfuration. Performance studies demonstrate that Bi2S3 with the largest lattice expansion (Bi2S3-9.7%, where 9.7% represents the lattice expansion) exhibits a greater electrocatalytic hydrogen evolution reaction (HER) activity compared to Bi2S3 and Bi2S3-3.2%. Density functional theory calculations reveal the expansion of the lattice spacing reduces the bandwidth and upshifts the band center of the Bi 3d orbits, facilitating electron exchange with the S 2p orbits. The resultant intrinsic electronic configuration exhibits favorable H* adsorption kinetics and a reduced energy barrier for water dissociation in hydrogen evolution. Operando Raman and post-mortem characterizations using XRD and X-ray photoelectron spectroscopy reveal the generation of pseudo-amorphous Bi at the edge of Bi2S3 nanorods of the sample with lattice strain during HER, yielding Bi2S3-9.7%-A. It is worth noting when Bi2S3-9.7%-A is assembled as a positive electrode in an asymmetric supercapacitor, its performance is greatly superior to that of the same device formed using pristine Bi2S3-9.7%. The as-prepared Bi2S3-9.7%-A//activated carbon asymmetric supercapacitor achieves a high specific capacitance of 307.4 F g−1 at 1 A g−1, exhibiting high retention of 84.1% after 10 000 cycles.

Monolayers of molybdenum disulfide are of vital importance in the fabrication of optical and nanoelectronic devices. The development of thin and low-cost devices has increased the demand for synthe...

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the ‘junctions’ between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

IrO2 is an important material in numerous applications ranging from catalysis to the microelectronics industry, but despite this its behaviour upon annealing under different conditions has not yet been thoroughly studied. This work provides a detailed investigation of the annealing of IrO2 thin films using in situ high-temperature X-ray diffraction and X-ray reflectivity (HTXRR) measurements from room temperature up to 1000°C in oxygen, nitrogen, forming gas and vacuum. Complementary ex situ scanning electron microscopy and atomic force microscopy measurements were conducted. The combined data show the dependencies of crystalline properties and surface morphology on the annealing temperature and atmosphere. The reduction of IrO2 to Ir takes place at a temperature as low as 150°C in forming gas, but in oxygen IrO2 is stable up to 800°C and evaporates as a volatile oxide at higher temperatures. The IrO2 crystallite size remains constant in oxygen up to 400°C and increases above that, while in the more reducing atmospheres the Ir crystallites grow continuously above the phase-change temperature. The role of HTXRR in the analysis is shown to be important since its high sensitivity allows one to observe changes taking place in the film at temperatures much below the phase change.

Herein, we report an atomic layer deposition (ALD) process for Cu2O thin films using copper(II) acetate [Cu(OAc)(2)] and water vapor as precursors. This precursor combination enables the deposition of phase-pure, polycrystalline, and impurity-free Cu2O thin films at temperatures of 180-220 degrees C. The deposition of Cu(I) oxide films from a Cu(II) precursor without the use of a reducing agent is explained by the thermally induced reduction of Cu(OAc)(2) to the volatile copper(I) acetate, CuOAc. In addition to the optimization of ALD process parameters and characterization of film properties, we studied the Cu2O films in the fabrication of photoconductor devices. Our proof-of-concept devices show that approx- imately 20 nm thick Cu2O films can be used for photodetection in the visible wavelength range and that the thin film photoconductors exhibit improved device characteristics in comparison to bulk Cu2O crystals.

Direct incorporation of Ni adatoms during graphene growth on Ni( 111) is evidenced by scanning tunneling microscopy. The structure and energetics of the observed defects is thoroughly characterized at the atomic level on the basis of density functional theory calculations. Our results show the feasibility of a simple scalable method, which could be potentially used for the realization of macroscopic practical devices, to dope graphene with a transition metal. The method exploits the kinetics of the growth process for the incorporation of Ni adatoms in the graphene network.

A low-cost and up-scalable fabrication method for high-quality gallium oxide films using spray pyrolysis from water-based solutions and moderate temperatures is presented. The solution chemistry and spraying process parameters were optimized to obtain homogeneous films on glass and three different transparent conducting oxide substrates. Structural and optical film properties of the deposited nanocrystalline Ga2O3 were evaluated by scanning electron microscopy, grazing-incidence X-ray diffraction, atomic force microscopy and optical spectroscopy. The elemental composition of the surface and the bulk film was analyzed by X-ray photoemission spectroscopy depth profiling. To show the applicability of the deposited Ga2O3 in electronic devices, the electronic valence region of the material was studied by ultraviolet photoemission spectroscopy, resulting in an energy level diagram of the material.

The development of active corrosion protection systems for metallic substrates is an issue of prime concern. The objective of this work was to demonstrate the applicability of plasma enhanced CVD (PECVD) in growing protective top oxide layers over sol-gel deposited organosiloxane (R-SiOx; water based inorganic-organic hybrid coating formulation containing 3-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane, crosslinked with hexamethylmethoxymelamine) coating to improve its thermal stability, chemical inertness and corrosion resistance. [MgAl2((OBu)-Bu-t)(4)H-4] and [AlH2((OBu)-Bu-t)](2) were used as single source precursors for depositing MgAl2O4 and Al2O3 thin films respectively. The coating systems namely, Al2O3/R-SiOx (ALSI) and MgAl2O4/R-SiOx (MALSI) were comparatively analyzed towards their corrosion protection behaviour. The post annealed PECVD deposited films were uniform, transparent and exhibited good adhesion as confirmed by focused ion beam scanning electron microscope (FIB-SEM) cross sectional analysis. ALSI and MALSI bilayer systems were found to be stable over temperatures as high as 600 degrees C. Corrosion performance of the coating systems effectively demonstrated the protective function of ALSI and MALSI bilayer system. However, it was observed that ALSI outperforms MALSI in this application.

Anisotropic growth of two-dimensional (2D) tungsten disulfide (WS2) crystals occurs during atomic layer deposition (ALD) from WS2 seeds at predetermined locations on large area dielectric substrates. The number of ALD reaction cycles determines the lateral dimensions of the WS2 crystals. This 2D synthesis approach is compatible with temperature sensitive structures due to the low deposition temperature and can be extended to other 2D materials and heterostructures thereof. The crystallinity of the seed and the selectivity of ALD precursors toward seeds and underlying starting surface affect the structural quality of the 2D crystals.

As a promising material used in accelerators and in space in the future, it is important to study the property and structural changes of graphene and diamond-like carbon on the surface as a protective layer before and after swift heavy ion irradiation, although this layer could have a loose structure due to the intrinsic sp(2) surrounding environment of graphene during its deposition period. In this study, by utilizing inelastic thermal spike model and molecular dynamics, we simulated swift heavy ion irradiation and examined the track radius in the vertical direction, as well as temperature, density, and sp(3) fraction distribution along the radius from the irradiation center at different time after irradiation. The temperature in the irradiation center can reach over 11000 K at the beginning of irradiation while there would be a low density and sp(3) fraction area left in the central region after 100 ps. Ring analysis also demonstrated a more chaotic cylindrical region in the center after irradiation. After comprehensive consideration, diamond-like carbon deposited by 70 eV carbon bombardment provided the best protection.

We have carried out a systematic investigation of the critical activation parameters (i.e., final temperature (673&ndash, 1273 K), atmosphere (He vs. O2/He), and final isothermal hold (1 min&ndash, 15 h) on the generation of &ldquo, &alpha, sites&rdquo, responsible for the direct N2O decomposition over Fe-ZSM-5 (Fe content = 1200&ndash, 2300 ppm). The concentration of &alpha, sites was determined by (ia) transient response of N2O and (ib) CO at 523 K, and (ii) temperature programmed desorption (TPD) following nitrous oxide decomposition. Transient response analysis was consistent with decomposition of N2O to generate (i) &ldquo, active&rdquo, oxygen that participates in the low-temperature CO&rarr, CO2 oxidation and (ii) &ldquo, non-active&rdquo, oxygen strongly adsorbed that is not released during TPD. For the first time, we were able to quantify the formation of &alpha, sites, which requires a high temperature (&gt, 973) treatment of Fe-ZSM-5 in He over a short period of time (&lt, 1 h). In contrast, prolonged high temperature treatment (1273 K) and the presence of O2 in the feed irreversibly reduced the amount of active sites.

Thin film deposition with atmospheric pressure plasmas is highly interesting for industrial demands and scientific interests in the field of biomaterials. However, the engineering of high-quality films by high-pressure plasmas with precise control over morphology and surface chemistry still poses a challenge. The two types of atmospheric-pressure plasma depositions of organosilicon films by the direct and indirect injection of hexamethyldisiloxane (HMDSO) precursor into a plasma region were chosen and compared in terms of the films chemical composition and morphology to address this. Although different methods of plasma excitation were used, the deposition of inorganic films with above 98% of SiO2 content was achieved for both cases. The chemical structure of the films was insignificantly dependent on the substrate type. The deposition in the afterglow of the DC discharge resulted in a soft film with high roughness, whereas RF plasma deposition led to a smoother film. In the case of the RF plasma deposition on polymeric materials resulted in films with delamination and cracks formation. Lastly, despite some material limitations, both deposition methods demonstrated significant potential for SiOx thin-films preparation for a variety of bio-related substrates, including glass, ceramics, metals, and polymers., This research was funded by EU H2020 M.Era-Net “PlasmaTex” project. Funding of the Romanian team was insured by the Romanian Ministry of Research and Innovation under the contract 31/2016/UEFISCDI. This work was funded by the Portuguese Foundation for Science and Technology FCT/MCTES (PIDDAC) and co-financed by European funds (FEDER) through the PT2020 program, research project M-ERA-NET/0006/2014. Slovenian team research was funded through the Ministry of Education, Science and Sport and Slovenian Research Agency (ARRS).

Passivating contacts are indispensable for achieving high conversion efficiency in crystalline-silicon solar cells. Their realization and integration into a convenient process flow have become crucial research objectives. Here, we report an alternative passivating contact that is formed in a single post-deposition annealing step called 'firing', an essential step for current solar cell manufacturing. As firing is a fast (750 degrees C) anneal, the required microstructural and electrical properties of the passivating contact are stringent. We demonstrate that tuning the carbon content of boron-doped silicon-based thin films inhibits firing-induced layer delamination without preventing a partial crystallization. The latter promotes charge-carrier selectivity, even in the absence of a diffused doped region beyond the oxide, by inducing hole accumulation near the wafer surface. We fabricated proof-of-concept solar cells employing the developed technology, demonstrating an open circuit voltage of 698 mV and an efficiency of 21.9%, and show how it could be a drop-in replacement for today's rear contacts based on locally opened dielectric passivation stacks.

Plasma-enhanced chemical vapor deposition (PECVD) was used to deposit SiOx thin films of varying thicknesses on parylene C substrates, using hexamethyldisiloxane (HMDSO) as a precursor. The microstructure of SiOx coatings was analyzed using X-ray photoemission spectroscopy (XPS), nanoindentation, and spectroscopic ellipsometry. The composition ranged from oxygen-rich oxides with large silanol OH content to hybrid oxides with larger organic content, while refractive index varied from 1.45 to 1.5 depending on the specimen. Reduced moduli of coatings obtained by nanoindentation varied between 15 and 59 GPa and could be correlated with permeability to oxygen and water vapor through the existence of porosity in a broader sense. It can be concluded that the barrier properties are the result of a complex interplay of microstructural features, with porosity, silanol, and carbon content playing important roles in the final thin film properties.

In this article, thin solid films are processed via pulsed-pressure metal organic chemical vapour deposition (PP-MOCVD) on FTO substrates over a range of processing times to produce a range of thicknesses and microstructures. The films are highly nanostructured anatase-rutile TiO2 composite films with unique single crystal dendrites. After annealing, carbon was removed, and materials showed improved water splitting activity; with IPCEs above 80% in the UV, photocurrents of ∼1.2 mA cm−2 at 1.23 VRHE at 1 sun irradiance and an extension of photoactivity into the visible range. The annealed material exhibits minimal recombination losses and IPCEs amongst the highest reported in the literature; attributed to the formation of a high surface area nanostructured material and synergetic interactions between the anatase and rutile phases.

Thin films of interstitial boron-doped anatase TiO2, with varying B concentrations, were deposited via one-step atmos-pheric pressure chemical vapour deposition (APCVD) on float glass substrates. The doped films showed a remarkable morphology and enhanced photoactivity when compared to their undoped analogues. The TiO2:B films also presented enhanced conductivity and electron mobility as measured by Hall Effect probe as well as a high adherence to the sub-strate, stability and extended lifetime. The structure and composition of the different samples of TiO2:B films were studied by X-ray Diffraction (XRD), Raman spectroscopy, Scanning Electron Microscopy (SEM) and Dynamic Second-ary Ion Mass Spectrometry (D-SIMS). Hybrid density functional theory was used to explore the defect chemistry of B-doped anatase and to understand the experimental results.

Ge nanowires are playing a big role in the development of new functional microelectronic modules, such as gate-all-around field-effect transistor devices, on-chip lasers and photodetectors. The widely used three-phase bottom-up growth method utilising a foreign catalyst metal or metalloid is by far the most popular for Ge nanowire growth. However, to fully utilise the potential of Ge nanowires, it is important to explore and understand alternative and functional growth paradigms such as self-seeded nanowire growth, where nanowire growth is usually directed by the in situ-formed catalysts of the growth material, i.e., Ge in this case. Additionally, it is important to understand how the self-seeded nanowires can benefit the device application of nanomaterials as the additional metal seeding can influence electron and phonon transport, and the electronic band structure in the nanomaterials. Here, we review recent advances in the growth and application of self-seeded Ge and Ge-based binary alloy (GeSn) nanowires. Different fabrication methods for growing self-seeded Ge nanowires are delineated and correlated with metal seeded growth. This review also highlights the requirement and advantage of self-seeded growth approach for Ge nanomaterials in the potential applications in energy storage and nanoelectronic devices.

Polycrystalline diamond films (similar to 10 mu m thick) were grown on five different silicon (Si) substrate orientations by microwave plasma chemical vapor deposition. The selected Si substrates had a range of f(theta): 0.18-0.65. It is to be noted that f(theta) scales inversely with the packing density of the interface. As f(theta) decreased, three changes in the polycrystalline diamond microstructures were observed. (i) At the film surface -fiber texture increased but -fiber dropped. (ii) A novel reconstruction technique was proposed and tested for faceted microstructures. The reconstructed microstructures revealed that the observed texture changes, with a decrease in f(theta), was accompanied by elimination of very fine facets. (iii) Noticeable differences in Raman estimated stress gradients were also observed: the lowest stress gradients for more closed packed substrates.

Silicon nitride (SixNy) and silicon oxynitride (SiOxNy) are materials that can find multifarious application in solar cells by tuning their microstructure and optical properties. In this work we have investigated a series of SixNy and SiOxNy films deposited by rf-PECVD at a low temperature of 200 degrees C having different compositional and optical properties by changing the gas mixture ratio during deposition resulting in varying refractive index materials. The effect of varying gas ratio on the composition of these materials has been investigated comprehensively by X-ray Photoelectron Spectroscopy (XPS) and the bond analysis using Fourier Transform Infrared Spectroscopy (FTIR) thereby creating a material library to select materials of desired properties and bond composition for specific applications in solar cells. The structural and optical properties were also analysed using Micro-Raman spectroscopy, X-ray Diffraction (XRD), UV-VIS-NIR spectrophotometer and ellipsometry. The films were found to be amorphous, hydrogenated, compact, presents high deposition rates and needs lesser thermal budget. In order to demonstrate their multifaceted application potential, we have fabricated multilayer anti-reflection coatings (ARC), novel Rugate ARC, dielectric Bragg mirrors using SiOxNy/SixNy multi layers as back reflectors for thin crystalline silicon (c-Si) wafers as well as the passivation of c-Si. The novel bilayer passivation stack over CZ p-type c-Si wafers using SiOxNy/SixNy presented a minority carrier lifetime of 169 mu s with an implied V-oc of 673 mV. (C) 2017 Elsevier B.V. All rights reserved.

Few studies reported the formation of Ti-containing clusters in the initial stages of TiO2 flame synthesis. The conversion from synthesis precursor to TiO2 monomers was commonly assumed to take place through global reaction such as thermal decomposition and/or hydrolysis at high temperatures. More recent studies have been able to identify stable intermediates of Ti-containing monomers, most commonly Ti(OH)(4), as the final step before the formation of TiO2. However, no larger Ti-containing cluster formation mechanisms or interactions between these monomers have been tracked. To investigate cluster formation pathways of TiO2 during flame synthesis, Charged clusters were measured in an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer. TiO2 nanoparticles were synthesized by adding titanium tetraisopropoxide (TTIP) precursor to a premixed CH4/O-2/N-2 flat flame aerosol reactor. Pure TiO2 clusters were not detected by the APi-TOF. Results from measured mass spectra and mass defect plots show that for positively charged clusters, the abstraction of CH2 groups occurs simultaneously with the clustering of larger intermediate organometallic species. For negatively charged clusters, NOx formation pathways in the flame may play a role during the initial stages of TiO2 formation, since a lot of Ti-containing clusters were attached with nitrate-related species. These research findings provide insights on quantum dot synthesis and molecular doping where rapid dilution of the flame synthesized nanoparticles is needed to better control the particle size and chemical composition. The possible influences of and potential artifacts brought by the dilution system on observing the incipient particle formation in flames were also discussed.

This paper shows a study on the variation of the flow ratio between oxygen and Hexamethyldisiloxane (HMDSO) in a hollow cathode arc PECVD process. Dynamic deposition rates were measured between 300 and 500 nm * m/ min. The deposited plasma polymer films were analyzed using visible light spectroscopy, X-ray photo -electron spectroscopy (XPS), X-ray reflectivity (XRR), Fourier -transformed infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and water vapor transmission rate (WVTR) measurements. The deposited samples were compared to a reactively sputtered SiO2 thin film. By increasing the oxygen to HMDSO flow ratio, the chemical, density and optical properties of the coating approached the sputtered Si02 film. However the permeation barrier of the SiO2 film only shows a slight improvement over that of the bare PET substrate. The organic coating with high power and low oxygen flow, which was deposited with a deposition rate of 450 nm * m/min, approached the barrier of the sputtered SiO2 thin film with a WVTR of 0.16 g/(m' day). 2016 Elsevier B.V. All rights reserved.

This paper deals with the engineering of the hetero-interface between intrinsic amorphous silicon (i-a-Si: H) layer and the n-type crystalline silicon (c-Si) wafer during the fabrication of the Silicon Heterojunction (SHJ) solar cell by the Hot Wire Chemical Vapor Deposition technique. It is known that this interface and the associated surface passivation of the c-Si is key to obtaining high efficiency heterojunction solar cells. The monitoring of this interface was carried out using high-resolution transmission electron microscopy (HRTEM). The HRTEM data of the c-Si/a-Si:H interface reveals a drastic dependence on the filament temperature (T-f) used during the deposition of the i-a-Si:H layer. Detailed analysis of the solar cell characteristics indicates that the cells where one has an abrupt crystalline/amorphous interface shows higher conversion efficiency compared to those where we have a rough and a defective interface or where there are indications of local epitaxy in the a-Si:H layer. The second parameter which was engineered is the bulk defect density of the intrinsic a-Si:H layer. Though the thickness of i-a-Si:H layer in case of SHJ solar cells is only around 5 nm and serves the purpose of passivating the dangling bonds on the c-Si wafer, the bulk defect density of this layer cannot be ignored. We have achieved a-Si:H films with acceptable bulk defect density without dilution of the silane gas with hydrogen. The bulk defect density of the i-a-Si:H layer has been determined by the constant photocurrent method (CPM) and is correlated to the performance of SHJ solar cells. A direct consequence of these control parameters was observed in the improvement of the external quantum efficiency near 600 nm wavelength region. (C) 2017 Elsevier Ltd. All rights reserved.

This paper reports the novel synthesis of amorphous Ta2O5 and the subsequent isolation of the orthorhombic (β) crystallographic phase, using aerosol-assisted chemical vapor deposition. Hybrid density functional theory was used to obtain the calculated optical band gap (3.83 eV) for the first time, which closely matches our experimental findings (3.85 eV). The films were highly transparent in the visible and near-IR region of the electromagnetic spectrum. The refractive indexes, calculated using the Swanepoel method, showed good agreement with literature findings. The photocatalytic properties of the films, determined through the photominerilization of stearic acid under 254 nm radiation showed the amorphous sample to be an order of magnitude superior over crystalline β-Ta2O5.

We demonstrate nanoscale wrinkling on polydimethylsiloxane (PDMS) at sub-100 nm length scales via a (double) frontal surface oxidation coupled with a mechanical compression. The kinetics of the glassy skin propagation is resolved by neutron and X-ray reflectivity, and atomic force microscopy, combined with mechanical wrinkling experiments to evaluate the resulting pattern formation. In conventional PDMS surface oxidation, the smallest wrinkling patterns attainable have an intrinsic lower wavelength limit due to the coupling of skin formation and front propagation at fixed strain εprestrain, whose maximum is, in turn, set by material failure. However, combining two different oxidative processes, ultra-violet ozonolysis followed by air plasma exposure, we break this limit by fabricating trilayer laminates with excellent interfacial properties and a sequence of moduli and layer thicknesses able to trivially reduce the surface topography to sub-100 nm dimensions. This method provides a powerful, yet simple, non-lithographic approach to extend surface patterning from visible to the deep UV range.

Heteroatom doping can effectively tune the structure and properties of graphene. Theoretical calculations indicate that sulfur doping can effectively modify the band structure and further modulate the carrier transport properties of graphene. However, it is still a big challenge to synthesize large-area sulfur-doped graphene (SG) films with a high sulfur doping concentration and reasonable electrical properties since sulfur has a much larger atomic radius than carbon. In this study, the solid organic source thianthrene (C12H8S2) is employed as both a carbon source and sulfur dopant to grow large-area, few-layered SG films via chemical vapor deposition (CVD). The results show that the doping concentration, doping configuration and electrical properties can be effectively tuned via the hydrogen flux. The sulfur doping concentration is as high as 4.01 at% and the maximal mobility of SG can reach up to 270 cm(2) V-1 s(-1), which are the highest ever reported for sulfur-doped graphene.

In order to understand, clarify and provide confirmations in the contexts of the prevalent confusions concerning Li-storage in graphenic carbon (viz. the reduced dimensional scale of graphitic carbon), electrochemical lithiation/delithiation has been performed with CVD-grown fairly pristine well-ordered few-layer graphene films (FLG; similar to 7 layers; as a model material). Chronopotentiograms and cyclic voltammograms recorded with the FLG present distinct features corresponding to the transformation between different Li-GICs (i.e., 'staging') below 0.3 V against Li/Li+, thus confirming that 'classical' Li-intercalation does occur even at such reduced dimensional (nano) scale. Nevertheless, even in this lower potential window (our main focus here), Li-storage in FLG involves contributions from both diffusion-and surface-controlled mechanisms. The Li-capacities recorded with FLG just within this lower potential window, and also upon subtracting any possible contribution from the Cu current collector, were still similar to 3-4 times greater than those obtained with similarly grown thicker bulk graphite films (TBG: similar to 450 nm; Li-capacity recorded: similar to 380 mA h g(-1)). Contrary to the usual belief, the excess Li-capacity of FLG cannot be explained by the presence of extrinsic/intrinsic defects, which are nearly negligible in the FLG films under consideration. Simulation of Li-storage in graphene via DFT indicated that the excess capacity (after formation of the LiC6 configuration) is associated with additional stable Li-storage on the outer graphene surfaces in the forms of more than one Li-layer (but different from Li-plating) and segregation close to the 'stepped' (exposed) edges of the inner graphene layers (but not exactly at the edge sites). Overall, such predicted Li-storage mechanisms are in agreement with the experimentally observed contributions from both 'classical' Li-intercalation and surface-controlled processes (even at potentials below 0.3 V), which primarily account for the excess Li-capacities recorded with graphenic carbon.

Contains fulltext : 166243.pdf (Publisher’s version ) (Closed access) Fe7Se8 exists as a hexagonal NiAs-like crystal structure with a large number of ordered intrinsic vacancies. It is an ideal candidate for studying the effect of defects on properties such as magnetism and electrical transport. In this work, highly crystalline Fe7Se8 with the 3c crystal structure was synthesized by a solid-state reaction. Sharp changes in the magnetization at 100 K confirm a rotation of the spins from the ab plane to the c axis with decreasing temperature. We observe an interesting metal–insulator transition at the same temperature as the spin-direction changes. We propose that locked spins in the grain boundaries induce electron localization and result in the metal–insulator transition. Electron localization is confirmed by X-ray photoelectron spectroscopy of the Fe 2p peaks, which exhibit two characteristic satellite peaks. This mechanism is also verified by comparing it with the properties of the 4c-Fe7Se8 crystal structure.

A plasma-enhanced atomic layer deposition (PE-ALD) process to deposit metallic gold is reported, using the previously reported Me3Au(PMe3) precursor with H-2 plasma as the reactant. The process has a deposition window from 50 to 120 degrees C with a growth rate of 0.030 +/- 0.002 nm per cycle on gold seed layers, and it shows saturating behavior for both the precursor and reactant exposure. X-ray photoelectron spectroscopy measurements show that the gold films deposited at 120 degrees C are of higher purity than the previously reported ones (

Gallium sulfide has a great potential for optoelectronic and energy storage applications. Since most of these applications require a high control over the layer thickness or a high conformality, atomic layer deposition is a promising deposition technique. In this work, the authors present a novel plasma enhanced atomic layer deposition process for gallium sulfide based on trimethylgallium and H 2 S/Ar plasma. The growth was characterized using in situ spectroscopic ellipsometry. It was found that the process grew linearly at a rate of 0.65 A/cycle and was self-limited in the temperature range from 70 to 350 °C. The process relied on a combustion reaction, which was shown by the presence of CS 2 during in situ mass spectrometry measurements. Furthermore, the material properties were investigated by x-ray photoelectron spectroscopy, x-ray diffraction, and optical transmission measurements. The as-deposited films were amorphous and pinhole free. The GaS x thin films had a transmittance of >90% and a band gap of 3.1–3.3 eV.Gallium sulfide has a great potential for optoelectronic and energy storage applications. Since most of these applications require a high control over the layer thickness or a high conformality, atomic layer deposition is a promising deposition technique. In this work, the authors present a novel plasma enhanced atomic layer deposition process for gallium sulfide based on trimethylgallium and H 2 S/Ar plasma. The growth was characterized using in situ spectroscopic ellipsometry. It was found that the process grew linearly at a rate of 0.65 A/cycle and was self-limited in the temperature range from 70 to 350 °C. The process relied on a combustion reaction, which was shown by the presence of CS 2 during in situ mass spectrometry measurements. Furthermore, the material properties were investigated by x-ray photoelectron spectroscopy, x-ray diffraction, and optical transmission measurements. The as-deposited films were amorphous and pinhole free. The GaS x thin films had a transmittance of >90%...

Boron carbide films are increasingly being investigated for their application in new generation neutron detectors. It is implemented as conversion layer for neutrons and emerging as a potential alternative to He-3 based detectors. This work reports synthesis of boron carbide (BxC) films from ortho-carborane (o-C2B10H12) by radio frequency (RF) plasma enhanced chemical vapour deposition (PECVD) technique. Dependence of chemical composition, stoichiometry and total macroscopic cross section (Sigma(t)) has been studied as a function of self-bias on the substrate, varied in the range -75 V to -175 V. Films were characterized by 3D optical profilometry, X-ray photoelectron spectroscopy (XPS), proton elastic back scattering spectrometry (p-EBS), Fourier transform infra-red spectroscopy (FTIR) and Field Emission Scanning Electron Microscope (FESEM). Characterization results show noticeable change in the bulk as well as surface chemical composition, surface morphology and film stoichiometry with self-bias. Neutron transmission measurements exhibit increase in Sigma(t) from 170.47 cm(-1) for -75 V film to 273.38 cm(-1) for -175 V film with self-bias. (C) 2016 Elsevier B.V. All rights reserved.

Carbon nanomaterial-based aerogels have attracted significant interests from both academia and industry due to their extremely low bulk density, tunable surface functionality, high specific surface area, dielectric strength and thermal and electrical properties, and diverse applications. There is currently a lack of understanding of how processing factors would determine the structure–property relationships important to the wide applications of these aerogels. The present work thoroughly examines the preparation, structure, properties and applications of three types of aerogels. Firstly, we briefly review carbon aerogels prepared from the sol–gel of certain organic monomers, where the synthesis and processing conditions determine the structural features, such as pore volume and pore size distribution. Secondly, carbon nanotube (CNT) aerogels made by three methods are discussed to identify their relative advantageous over carbon aerogels in terms of electrical conductivity and mechanical robustness. Finally, graphene aerogels are reviewed, which can be prepared by four routes—template-directed CVD, in situ reduction assembly, template-directing assembly and cross-linking. In comparison with CNT aerogels, graphene aerogels can be made at lower manufacturing costs to achieve appropriate properties meeting various needs. The major applications of these aerogels include flexible energy storage devices and environmental applications, both of which exploit the key characteristics of carbon aerogels such as low density and high porosity, deformability, mechanical robustness, electrical conductivity, adsorption and electro-sorption. Challenges, research opportunities and future applications are also discussed. Refereed/Peer-reviewed

We report a time-resolved approach to probe the mechanical properties of thin films during drying and solidification based on surface wrinkling. The approach is demonstrated by measuring the modulus of a ternary system comprising an inorganic salt (aluminum chlorohydrate), a humectant (glycerol), and water across the glassy film formation pathway. The topography of mechanically induced wrinkling of supported films on polydimethylsiloxane (PDMS) is experimentally monitored during mechanical extension and relaxation cycles. Nontrivial aspects of our method include the need to oxidize the (hydrophobic) PDMS surface prior to solution deposition to enable surface wetting, which simultaneously creates a glassy-layer skin, whose wrinkling can contribute to the overall topography. Film drying is studied as a function of solution concentration and time, and a range of pattern morphologies are found: sinusoidal wrinkling, transient double-wavelength wrinkling accompanying film "crust" formation, ridging associated with stress localization, and cracking. We quantify the evolution of the elastic modulus during the sinusoidal wrinkling stage, employing bi- and trilayer models, which are independently confirmed by nanoindentation. The method provides thus a simple and robust approach for the mechanical characterization of out-of-equilibrium thin films.

This work describes the processability of insoluble or partially soluble polymers based on 3,4-alkylenedioxythiophene (ADOT). Functional and structural variants of poly(3,4-alkylenedioxythiophene) (PADOTs), P1(a-e), are synthesized, in which the side chain bulkiness was minimized to obtain better planarity and strong pi-interaction. P1(a-e) were synthesized via chemical coupling polymerization using palladium acetate as the catalyst. Subsequent polymers structures (P1a to P1e) were obtained with either an enhanced alkylenedioxy bridge and or a side chain substituent in the alternate repeating units. Polymers P1(a-c) are insoluble in all common organic solvents, whereas the hydroxyl functional polymers P1(d-e) are soluble in organic polar solvents, which absorb at 535 nm and display optical properties both in solution and solid state. The conductivity of the oxidized thin films of the soluble polymers P1d and P1e is 4.7 S cm(-1) and 1.5 S cm(-1), respectively. The neutral P1(a-e) polymers were dispersed in aqueous media using polystyrenesulfonate (PSS) and oxidized with sodium persulfate (Na2S2O8). The particle size, stability and ion contents of these aqueous dispersions were characterized via various spectroscopic techniques. The thin films of the P1(a-e): PSS dispersions were transparent with conductivity ranging from 8.1 x 10(-2) to 1.2 x 10(-2) S cm(-1). Spectroelectrochemical studies show that the P1(a-e): PSS polymer films switch between opaque blue to a transmissive oxidized state with optical contrast in the range of 40-46%.

Reductive grafting with mPEG is effective on a wide range of carbon nanomaterials. However, 2D forms are most effective as protein nucleants., A range of carbon nanomaterials, with varying dimensionality, were dispersed by a non-damaging and versatile chemical reduction route, and subsequently grafted by reaction with methoxy polyethylene glycol (mPEG) monobromides. The use of carbon nanomaterials with different geometries provides both a systematic comparison of surface modification chemistry and the opportunity to study factors affecting specific applications. Multi-walled carbon nanotubes, single-walled carbon nanotubes, graphite nanoplatelets, exfoliated few layer graphite and carbon black were functionalized with mPEG-Br, yielding grafting ratios relative to the nanocarbon framework between ca. 7 and 135 wt%; the products were characterised by Raman spectroscopy, TGA-MS, and electron microscopy. The functionalized materials were tested as nucleants by subjecting them to rigorous protein crystallization studies. Sparsely functionalized flat sheet geometries proved exceptionally effective at inducing crystallization of six proteins. This new class of nucleant, based on PEG grafted graphene-related materials, can be widely applied to promote the growth of 3D crystals suitable for X-ray crystallography. The association of the protein ferritin with functionalized exfoliated few layer graphite was directly visualized by transmission electron microscopy, illustrating the formation of ordered clusters of protein molecules critical to successful nucleation.

For large-scale atomic layer deposition (ALD) of alumina, the most commonly used alkyl precursor trimethylaluminum poses safety issues due to its pyrophoric nature. In this work, the authors have investigated a liquid alkoxide, aluminum tri-sec-butoxide (ATSB), as a precursor for ALD deposition of alumina. ATSB is thermally stable and the liquid nature facilitates handling in a bubbler and potentially enables liquid injection toward upscaling. Both thermal and plasma enhanced ALD processes are investigated in a vacuum type reactor by using water, oxygen plasma, and water plasma as coreactants. All processes achieved ALD deposition at a growth rate of 1-1.4 angstrom/cycle for substrate temperatures ranging from 100 to 200 degrees C. Film morphology, surface roughness, and composition have been studied with different characterization techniques. Published under license by AVS.

In this study, the authors demonstrate improved p-type Mg dopant activation near surface by P ion implantation, which otherwise remain inactive due to a combination of self compensation, formation of Mg-H complexes and high activation energy. The improvement is mainly attributed to the reduction in self-compensation by a reduction in N vacancies near the surface and potential formation of by-products suppressing Mg-H complexes. In addition, inclusion of P by plasma-immersion ion implantation creates a non-uniform dopant activation leading to a built-in electric field which further assists in ionizing the Mg dopants. The near-surface improved p- dopant activation is manifested as a reduction in the contact resistance and specific contact resistivity. The contact resistance and specific contact resistivity are found to decrease by 68.7 and 77.4%, respectively, for P implanted p-GaN samples in comparison to that of the control samples. The enhanced p-doping is found to increase electro-luminescence intensity by 264% for P implanted p-top electrically injected light emitting diodes. The improved p-type properties for GaN may find potential applications in the realization of electrically injected high efficiency optoelectronic devices.

Semiconducting 2D materials, such as SnS2, hold immense potential for many applications ranging from electronics to catalysis. However, deposition of few-layer SnS2 films has remained a great challenge. Herein, continuous wafer-scale 2D SnS2 films with accurately controlled thickness (2 to 10 monolayers) are realized by combining a new atomic layer deposition process with low-temperature (250 degrees C) postdeposition annealing. Uniform coating of large-area and 3D substrates is demonstrated owing to the unique self-limiting growth mechanism of atomic layer deposition. Detailed characterization confirms the 1T-type crystal structure and composition, smoothness, and continuity of the SnS2 films. A two-stage deposition process is also introduced to improve the texture of the films. Successful deposition of continuous, high-quality SnS2 films at low temperatures constitutes a crucial step toward various applications of 2D semiconductors.

Reactions of the free tantalum cation, Ta+, and tantalum cluster cations, Ta-n(+) (n = 2-10), with ammonia are presented. The reaction of the monomer cation, Ta+, with two molecules of NH3 leads to the formation of TaN2H2+ along with release of two H-2 molecules. The dehydrogenation occurs until the formal oxidation number of the tantalum atom reaches +5. On the other hand, all the tantalum cluster cations, Ta-n(+), react with two molecules of NH3 and form TanN2+ with the release of three H-2 molecules. Further exposure to ammonia showed that TanNmH+ and TanNm+ are produced through successive reactions; a pure nitride and three H-2 molecules are formed for every other NH3 molecule. The nitridation occurred until the formal oxidation number of the tantalum atoms reaches +5 as in the case of TaN2H2+ in contrast to other group 5 elements, i.e., vanadium and niobium, which have been reported to produce nitrides with lower oxidation states. The present results on small gas-phase metal-nitride clusters show correlation with their bulk properties: tantalum is known to form bulk nitrides in the oxidation states of either +5 (Ta3N5) or +3 (TaN), whereas vanadium and niobium form nitrides in the oxidation state of +3 (VN and NbN). Along with DFT calculations, these findings reveal that nitridation is driven by the electron-donating ability of group 5 elements, i.e., electronegativity of the metal plays a key role in determining the composition of the metal nitrides.

Three-dimensional sulfur-doped graphene (3DSG) with high sulfur-doping content (2.9%) was synthesized on nickel foam by chemical vapor deposition using solid organic source of thianthrene as both the carbon source and sulfur dopant. The 3DSG further treated by Ar plasma (3DSG-Ar) was demonstrated as a free-standing and binder-free electrocatalyst without any polymeric binders for electrode fabrication. Particularly, 3DSG-Ar can be used as highly effective and stable electrocatalyst for hydrogen evolution reaction (HER). It delivers a very low Tafel slope of 64 mV dec(-1), which is superior or comparable to most metal-free carbon-based electrocatalysts ever reported; moreover, it shows superior long-term electrocatalytic stability even after 2000 cycles. The excellent HER performances of 3DSG-Ar can be attributed to its well-designed porous, conductive and flexible 3D sulfur-doped graphene structure. Sulfur doping combing with plasma treatment cause a synergistic effect to effectively provide many more electrocatalytic active sites, resulting in significantly improved HER performance. In addition, the conductive, porous and flexible 3D graphene skeleton can not only act as free-standing and binder-free electrocatalytic electrode, but also guarantee the interconnected conductive paths in the whole electrode, leading to facilitate the charge transportation between the electrocatalyst and electrolyte and thus enhance its HER performances.

Producción Científica, Five-layer crystalline thin film structures were formed, consisting of ZrO2 and Co3O4 alternately grown on Si(100) substrates by atomic layer deposition at 300°C using ZrCl4 and Co(acac)3 as the metal precursors and ozone as the oxygen precursor. The performance of the laminate films was dependent on the relative content of constituent oxide layers. The magnetization in these films was nonlinear, saturative, and with very weak coercive fields. Electrical measurements revealed the formation of significant polarization versus external field loops and implied some tendency toward memristive behavior., Fondo Europeo de Desarrollo Regional (project TK134), Estonian Research Agency (grants IUT2-24 and PRG4), Ministerio de Economía, Industria y Competitividad (grant TEC2017-84321-C4-2-R)

The renewable energy revolution and its practical applications demand the need for large solar storage options. Lithium-ion batteries may remain top in terms of their utilization and performance, however their cost-per-kWh impacts their usage, and researchers prefer to stick to sodium-ion chemistry as a large storage option. One of the main research topics for rechargeable sodium-ion batteries is in proposing new anodes, since the commercial graphite anode is incompatible for use in SIBs as its larger radius (0.98 angstrom vs. 0.69 angstrom of Li+) leads to sluggish Na-ion transport during the cycling process. Our team is continuously working on the development of chalcogenide-based anodes for use in sodium-ion batteries and their reaction mechanisms. In this work, we prepared MoSe2 and MoSe2-N, P-doped rGO composites (with the latter denoted as MoSe2/NPr) as active anodes for use in sodium-ion batteries. The morphology and electrochemical properties of MoSe2/NPr were characterised and compared with those of the bare MoSe2 electrode. The MoSe2/NPr composite delivers a capacity of 337 mA h g(-1) at 0.1 A g(-1) after 100 cycles and 244.4 mA h g(-1) at 1 A g(-1); these values are higher than those of MoSe2/rGO (225.6 mA h g(-1) at 0.1 A g(-1)) and MoSe2 electrodes (206 mA h g(-1) at 0.1 A g(-1)). The excellent performance of MoSe2/NPr is attributed to the interconnected doped rGO sheets that provide sufficient active sites for MoSe2 with improved conductivity and reduced volume expansion during the cycling process. In addition, the sodium storage mechanism is investigated by several ex situ physical and microscopic studies.

International audience; Organosilicon films were deposited on carbon steel using plasma enhanced chemical vapour deposition (PECVD) process prepared from cold plasma polymerization of 1,1,3,3-tetramethyldisiloxane (TMDSO). The experimental design technique allowed determining the optimal conditions of the plasma process. The effect of different surface pretreatments was investigated using amorphous phosphatation, argon (Ar) and nitrogen (N2) plasma. Coatings showing a hydrophobic character and good adhesion were obtained. Several surface characterization techniques using Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), contact angle, cross-cut and surface profilometry were used. The protection efficiency against corrosion of the deposited films has been demonstrated by coupling different electrochemical techniques such as open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) in 3 wt% NaCl solution. The organosilicon coatings showed good barrier against corrosion even after long immersion time in the aggressive environment, especially when N2 plasma pretreatment is performed.

Carbon films and coatings are industrially very versatile and have a multiplicity of applications, such as conductive coatings or chemical and thermal protection layers. However, in most cases they are fabricated by the expensive vapor process, which has prevented a wider commercialization of these products. Herein, carbon films are fabricated using an inexpensive polymer-solution-based or sol–gel coating process, exemplified by spin coating of thin layers. As carbon precursor, the oligomeric form of acrodam, a high nitrogen-containing and non-volatile compound which is known to have excellent carbon yields, was employed. The oligomer is synthesized from commercially available starting materials (diaminomaleonitrile (DAMN) and acrolein) and dissolves in various organic solvents. The carbonized films were found to be homogeneous, optically flat, void- and crack-free, and were fabricated with up to 800 nm thickness after a carbonization step. High conductivities (up to 334 S cm −1 ) were achieved at the carbonization temperature of 1000 °C.

The direct chemical vapor deposition of WS2 by W(CO)(6) and elemental sulfur as precursors onto epitaxial-graphene on SiC and CVD-graphene transferred on SiO2/Si substrate is presented. This methodology allows the epitaxial growth of continuous WS2 films with a homogeneous and narrow photoluminescence peak without inducing stress or structural defects in the graphene substrates. The control of the WS2 growth dynamics for providing the localized sulfide deposition by tuning the surface energy of the graphene substrates is also demonstrated. This growth methodology opens the way towards the direct bottom up fabrication of devices based on TMDCs/graphene van der Waals heterostructures.

The structural and luminescent properties of InxAl1-xN/Al0.53Ga0.47N multiple quantum wells (MQW) grown on an Al0.5Ga0.5N buffer partially relaxed with respect to an underlying AlN-template are reported. A significant redshift and improvement of ultraviolet (UV) photoluminescence (PL) intensity is found for InAlN MQWs grown on AlGaN buffers with higher relaxation degree. This is attributed to a higher QW indium incorporation as confirmed also by X-ray diffraction (XRD). The nature of room temperature time resolved PL is studied and discussed from the point of view of the possibility of a type I-type II band lineup transition in the InAlN-AlGaN system.

Molybdenum disulfide (MoS2) is a semiconducting 2D material, which has evoked wide interest due to its unique properties. However, the lack of controlled and scalable methods for the production of MoS2 films at low temperatures remains a major hindrance on its way to applications. In this work, atomic layer deposition (ALD) is used to deposit crystalline MoS2 thin films at a relatively low temperature of 300 degrees C. A new molybdenum precursor, Mo(thd)(3) (thd = 2,2,6,6-tetramethylheptane-3,5-dionato), is synthesized, characterized, and used for film deposition with H2S as the sulfur precursor. Self-limiting growth with a low growth rate of approximate to 0.025 angstrom cycle(-1), straightforward thickness control, and large-area uniformity are demonstrated. Film crystallinity is found to be relatively good considering the low deposition temperature, but the films have significant surface roughness. Additionally, chemical composition as well as optical and wetting properties are evaluated. MoS2 films are deposited on a variety of substrates, which reveal notable differences in growth rate, surface morphology, and crystallinity. The growth of crystalline MoS2 films at comparably low temperatures by ALD contributes toward the use of MoS2 for applications with a limited thermal budget.

Controllable growth of highly crystalline transition metal dichalcogenide (TMD) patterns with regular morphology and unique edge structure is highly desired and important for fundamental research and potential applications. Here, single-crystalline MoS2 flakes are reported with regular trigonal symmetric patterns that can be homoepitaxially grown on MoS2 monolayer via chemical vapor deposition. The highly organized MoS2 patterns are rhombohedral (3R)-stacked with the underlying MoS2 monolayer, and their boundaries are predominantly terminated by zigzag Mo edge structure. The epitaxial MoS2 crystals can be tailored from compact triangles to fractal flakes, and the pattern formation can be explained by the anisotropic growth rates of the S and Mo edges under low sulfur chemical potential. The 3R-stacked MoS2 pattern demonstrates strong second and third-harmonic-generation signals, which exceed those reported for monolayer MoS2 by a factor of 6 and 4, correspondingly. This homoepitaxial growth approach for making highly organized TMD patterns is also demonstrated for WS2 .

It has been more than 40 years since Fujishima and Honda demonstrated water splitting using TiO2, yet there is still no clear mechanism by which surface holes on TiO2 oxidize water. In this paper, we use a range of complementary techniques to study this reaction that provide a unique insight into the reaction mechanism. Using transient photocurrent and transient absorption spectroscopy, we measure both the kinetics of electron extraction (t(50%) approximate to 200 mu s, 1.5V(RHE)) and the kinetics of hole oxidation of water (t(50%) approximate to 100 ms, 1.5V(RHE)) as a function of applied potential, demonstrating the water oxidation by TiO2 holes is the kinetic bottleneck in this water-splitting system. Photoinduced absorption spectroscopy measurements under 5 s LED irradiation are used to monitor the accumulation of surface TiO2 holes under conditions of photoelectrochemical water oxidation. Under these conditions, we find that the surface density of these holes increases nonlinearly with photocurrent density. In alkali (pH 13.6), this corresponded to a rate law for water oxidation that is third order with respect to surface hole density, with a rate constant k(WO) = 22 +/- 2 nm(4).s(-1). Under neutral (pH = 6.7) and acidic (pH = 0.6) conditions, the rate law was second order with respect to surface hole density, indicative of a change in reaction mechanism. Although a change in reaction order was observed, the rate of reaction did not change significantly over the wide pH range examined (with TOFs per surface hole in the region of 20-25 s(-1) at similar to 1 sun irradiance). This showed that the rate-limiting step does not involve OH- nucleophilic attack and demonstrated the versatility of TiO2 as an active water oxidation photocatalyst over a wide range of pH.

We present an in-depth first-principles study of the lattice dynamics of the tin sulphides SnS2, Pnma and π-cubic SnS and Sn2S3. An analysis of the harmonic phonon dispersion and vibrational density of states reveals phonon bandgaps between low- and high-frequency modes consisting of Sn and S motion, respectively, and evidences a bond-strength hierarchy in the low-dimensional SnS2, Pnma SnS and Sn2S3 crystals. We model and perform a complete characterisation of the infrared and Raman spectra, including temperature-dependent anharmonic linewidths calculated using many-body perturbation theory. We illustrate how vibrational spectroscopy could be used to identify and characterise phase impurities in tin sulphide samples. The spectral linewidths are used to model the thermal transport, and the calculations indicate that the low-dimensional Sn2S3 has a very low lattice thermal conductivity, potentially giving it superior performance to SnS as a candidate thermoelectric material.