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Silver orthophosphate is a highly promising visible light photocatalyst with high quantum yield for solar driven water oxidation. Recently, the performance of this material has been further enhanced using facet-controlled synthesis. The tetrahedral particles with {111} exposed facets demonstrate higher photocatalytic performance than the cubic particles with {100} exposed facets. However, the reason behind this large difference in photocatalytic performance is still not understood. In this work, we study the free charge carrier dynamics, such as mobility, lifetime, and diffusion lengths, for the {111}-faceted tetrahedral and the {100}-faceted cubic particles using time-resolved microwave conductivity measurements. An order of magnitude higher charge carrier mobility and diffusion length are found for the tetrahedral particles as compared to the cubic particles. The differences in crystal structure, surface composition, and optical properties are investigated in order to understand how these properties impact the charge carrier dynamics and the photocatalytic performance of differently faceted particles. [ABSTRACT FROM AUTHOR]

Angle resolved x-ray photoelectron spectroscopy (ARXPS) has been employed to determine nondestructively the in-depth interface formation during thin film growth. Buried interfaces underneath the nanometer thick layers are probed by identifying the chemical shift of compound materials in photoelectron spectroscopy and using the angular response to quantify the compound amounts from the measured intensities. The thin interfaces in molybdenum-silicon multilayers grown at ambient temperature are investigated. This system is an example of an almost perfect 1D-system, where the interface region is only a small part of the individual layer thicknesses of 3 to 5 nm. Despite the low growth temperature, both the interfaces of this multilayer show layer thickness dependent interface formation. While the silicon-on-molybdenum interface shows a limited interface thickness of 0.4 nm of Mo5Si3, the molybdenum-on-silicon interface shows a more complex evolution. For this interface, the composition of the first 2.0 nm of deposited layer thickness is best described as a molybdenum-silicon compound layer with a molybdenum rich top and a MoSi2 bottom layer. After 2.5 nm of the deposited layer thickness, the molybdenum rich compound at the top has transformed into polycrystalline molybdenum on top of 1.8 nm MoSi2 at the interface. The formation of the 1.8 nm MoSi2 precedes the formation of polycrystalline molybdenum on top. Angle resolved x-ray photoelectron spectroscopy (ARXPS) is shown to be a good tool to study the interface phenomena beneath the nanometer thick top layers. In the case of Mo/Si multilayer mirrors, this ARXPS study shows that the compound formation at the interface accounts for the majority of the extreme ultraviolet reflectance loss. [ABSTRACT FROM AUTHOR]

The photoelectrochemical (PEC) activity of microstructured electrodes remains low despite the highly enlarged surface area and enhanced light harvesting. To obtain a deeper understanding of the effect of 3D geometry on the PEC performance, well‐defined WO3/n‐Si and WO3/pn‐Si micropillar arrays are fabricated and subjected to a quantitative analysis of the relationship between the geometry of the micropillars (length, pitch) and their PEC activity. For WO3/n‐Si micropillars, it is found that the photocurrent increases for WO3/n‐Si pillars, but not in proportion to the increase in surface area that results from increased pillar length or reduced pillar pitch. Optical simulations show that a reduced pillar pitch results in areas of low light intensity due to a shadowing effect. For WO3/pn‐Si micropillar photoelectrodes, the p–n junction enhances the photocurrent density up to a factor of 4 at low applied bias potential (0.8 V vs RHE) compared to the WO3/n‐Si. However, the enhancement in photocurrent density increases first and then decreases with reduced pillar pitch, which scales with the photovoltage generated by the p–n junction. This is related to an increased dead layer of the p–n junction Si surface, which results in a decreased photovoltage even though the total surface area increases. [ABSTRACT FROM AUTHOR]

Ion sputtering yields for Ru, Mo, and Si under Ar+ ion bombardment in the near-threshold energy range have been studied using an in situ weight-loss method with a Kaufman ion source, Faraday cup, and quartz crystal microbalance. The results are compared to theoretical models. The accuracy of the in situ weight-loss method was verified by thickness-decrease measurements using grazing incidence x-ray reflectometry, and results from both methods are in good agreement. These results provide accurate data sets for theoretical modeling in the near-threshold sputter regime and are of relevance for (optical) surfaces exposed to plasmas, as, for instance, in extreme ultraviolet photolithography. [ABSTRACT FROM AUTHOR]

Chemical diffusion and interlayer formation in thin layers and at interfaces is of increasing influence in nanoscopic devices, such as nanoelectronics and reflective multilayer optics. Chemical diffusion and agglomeration at interfaces of thin Ru, Mo, Si, and B4C layers have been studied with x-ray photoelectron spectroscopy, cross section electron energy loss spectroscopy, high-angle annular dark field scanning transmission electron microscopy, and energy dispersive x-ray in relation to observations in Ru-on-B4C capped Mo/Si multilayers. Rather than in the midst of the Si layer, silicides and borides are formed at the Si-on-Mo interface front, notably RuSix and MoBx. The interface apparently acts as a precursor for further chemical diffusion and agglomeration of B, Ru, and also other investigated d-metals. Reversed "substrate-on-adlayer" interfaces can yield entirely suppressed reactivity and diffusion, stressing the influence of surface free energy and the supply of atoms to the interface via segregation during thin layer growth. [ABSTRACT FROM AUTHOR]

Reflective Si/Mo multilayer mirrors with protective d-metal surfaces onto a range of upper Mo and Si layer thicknesses have been grown with physical vapor deposition and investigated on diffusion and in-depth compound formation. Laterally inhomogeneous upward Si and downward d-metal diffusion occurs through Mo layers up to 2 nm thickness. Especially Ru and Rh agglomerate and form silicides such as Ru2Si3 and Rh2Si not in the midst of the Si layer but at the Si/Mo interface. This appears to be mediated by MoSi2 presence at the Si/Mo interface that acts as precursor via better lattice compatibility and lowering of formation energy. [ABSTRACT FROM AUTHOR]

In situ weight-loss method with a Kaufman ion source, Faraday cup, and quartz crystal microbalance are used for studying the ion sputtering yields for Ru, Mo, and Si under [Ar.sup.+] ion bombardment in the near-threshold energy range. The results have provided accurate data sets for theoretical modeling in the near-threshold sputter regime and are relevant for optical surfaces exposed to plasmas in extreme ultraviolet photolithography.

Non‐oxidative methane activation is carried out in a microwave plasma reactor for coupling to higher hydrocarbons. Fourier transform infrared spectroscopy (FTIR) was used to measure absolute concentrations of the major hydrocarbon species. Hydrogen concentration was also independently inferred from pressure‐based change in molar flow measurements. By closing both the carbon and hydrogen balance, from stoichiometry of the reactions, the amount of deposits was obtained as well. Additionally, core gas temperatures up to 2500 K were measured with Raman scattering when nitrogen acted as probing molecule in sample mixture discharges. At low gas temperatures, ethane and ethylene were significant products based on plasma chemistry, with ethane selectivities reaching up to 60%. At higher gas temperatures, thermal effects become stronger shifting the selectivity toward acetylene and deposits, resembling more with equilibrium calculations. The energy efficiency of the methane conversion reached up to 15% from which 10% represented coupling efficiency to higher hydrocarbons. It is concluded that there is an interplay between plasma and thermal chemistry where plasma generates radicals and final distribution is set by thermodynamics. Non‐oxidative low pressure microwave discharges in methane show high ethane selectivity most likely as a result of methyl radical dimerization. The result highlights the potential of using microwave plasmas as (methyl)radical source that can give an extra degree of freedom for the design of novel coupling catalysts. [ABSTRACT FROM AUTHOR]

Silver orthophosphate is a highly promising visible light photocatalyst with high quantum yield for solar driven water oxidation. Recently, the performance of this material has been further enhanced using facet-controlled synthesis. The tetrahedral particles with {111} exposed facets demonstrate higher photocatalytic performance than the cubic particles with {100} exposed facets. However, the reason behind this large difference in photocatalytic performance is still not understood. In this work, we study the free charge carrier dynamics, such as mobility, lifetime, and diffusion lengths, for the {111}-faceted tetrahedral and the {100}-faceted cubic particles using time-resolved microwave conductivity measurements. An order of magnitude higher charge carrier mobility and diffusion length are found for the tetrahedral particles as compared to the cubic particles. The differences in crystal structure, surface composition, and optical properties are investigated in order to understand how these properties impact the charge carrier dynamics and the photocatalytic performance of differently faceted particles.