Interface and surface analysis of Ru/CdS
01 Jan 1996-Journal of Materials Science Letters (Kluwer Academic Publishers)-Vol. 15, Iss: 21, pp 1921-1923
About: This article is published in Journal of Materials Science Letters.The article was published on 1996-01-01. It has received 4 citations till now.
TL;DR: For a variety of metals and semiconductors, an attempt is made to generalize observations in the literature on the effect of process conditions applied during photodeposition on (i) particle size distributions, (ii) oxidation states of the metals obtained, and (iii) consequences for photocatalytic activities.
Abstract: In this review, for a variety of metals and semiconductors, an attempt is made to generalize observations in the literature on the effect of process conditions applied during photodeposition on (i) particle size distributions, (ii) oxidation states of the metals obtained, and (iii) consequences for photocatalytic activities. Process parameters include presence or absence of (organic) sacrificial agents, applied pH, presence or absence of an air/inert atmosphere, metal precursor type and concentration, and temperature. Most intensively reviewed are studies concerning (i) TiO2; (ii) ZnO, focusing on Ag deposition; (iii) WO3, with a strong emphasis on the photodeposition of Pt; and (iv) CdS, again with a focus on deposition of Pt. Furthermore, a detailed overview is given of achievements in structure-directed photodeposition, which could ultimately be employed to obtain highly effective photocatalytic materials. Finally, we provide suggestions for improvements in description of the photodeposition methods applied when included in scientific papers.
TL;DR: It is demonstrated further that a fine control of the metal Ru nanoparticle size on the TiO2 support was possible via a controlled nanocluster growth under irradiation, while the nanoparticles revealed a good resistance to thermal sintering.
Abstract: Ru/TiO₂ are promising heterogeneous catalysts in different key-reactions taking place in the catalytic conversion of biomass towards fuel additives, biofuels, or biochemicals. TiO₂ supported highly dispersed nanometric-size metallic Ru catalysts were prepared at room temperature via a solar light induced photon-assisted one-step synthesis in liquid phase, far smaller Ru nanoparticles with sharper size distribution being synthesized when compared to the catalysts that were prepared by impregnation with thermal reduction in hydrogen. The underlying strategy is based on the redox photoactivity of the TiO₂ semi-conductor support under solar light for allowing the reduction of metal ions pre-adsorbed at the host surface by photogenerated electrons from the conduction band of the semi-conductor in order to get a fine control in terms of size distribution and dispersion, with no need of chemical reductant, final thermal treatment, or external hydrogen. Whether acetylacetonate or chloride was used as precursor, 0.6 nm sub-nanometric metallic Ru particles were synthesized on TiO₂ with a sharp size distribution at a low loading of 0.5 wt.%. Using the chloride precursor was necessary for preparing Ru/TiO₂ catalysts with a 0.8 nm sub-nanometric mean particle size at 5 wt.% loading, achieved in basic conditions for benefitting from the enhanced adsorption between the positively-charged chloro-complexes and the negatively-charged TiO₂ surface. Remarkably, within the 0.5⁻5 wt.% range, the Ru content had only a slight influence on the sub-nanometric particle size distribution, thanks to the implementation of suitable photo-assisted synthesis conditions. We demonstrated further that a fine control of the metal Ru nanoparticle size on the TiO₂ support was possible via a controlled nanocluster growth under irradiation, while the nanoparticles revealed a good resistance to thermal sintering.
TL;DR: In this paper, the effect of the variation of the incident irradiance and photodeposition rate on the photocatalytic properties of ruthenium nanoparticles supported on TiO2 was evaluated by using the degradation of formic acid in water under UV-A light.
Abstract: Photoassisted synthesis is as a highly appealing green procedure for controlled decoration of semiconductor catalysts with co-catalyst nanoparticles, which can be carried out without the concourse of elevated temperatures, external chemical reducing agents or applied bias potential and in a simple slurry reactor. The aim of this study is to evaluate the control that such a photoassisted method can exert on the properties of ruthenium nanoparticles supported on TiO2 by means of the variation of the incident irradiance and hence of the photodeposition rate. For that purpose, different Ru/TiO2 systems with the same metal load have been prepared under varying irradiance and characterized by means of elemental analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. The photocatalytic activity of the so-obtained materials has been evaluated by using the degradation of formic acid in water under UV-A light. Particles with size around or below one nanometer were obtained, depending on the irradiance employed in the synthesis, with narrow size distribution and homogeneous dispersion over the titania support. The relation between neutral and positive oxidation states of ruthenium could also be controlled by the variation of the irradiance. The obtained photocatalytic activities for formic acid oxidation were in all cases higher than that of undecorated titania, with the sample obtained with the lowest irradiation giving rise to the highest oxidation rate. According to the catalysts characterization, photocatalytic activity is influenced by both Ru size and Ru0/Ruδ+ ratio.
TL;DR: In this article, the changes in RuCl 3 formation and surface roughness with various cleaning processes were investigated and it was confirmed that, during Cl 2 dry etching to remove the absorber layer, RuCl3 was formed on the Ru capping layer surface, and the surface roughs thereby deteriorated.
Abstract: Ru-capped extreme ultraviolet lithography photomasks require cleaning after patterning of the absorber layer. In this study, it was confirmed that, during Cl 2 dry etching to remove the absorber layer, RuCl 3 was formed on the Ru capping layer surface, and the surface roughness thereby deteriorated. Therefore, the changes in RuCl 3 formation and surface roughness with various cleaning processes were investigated. Among the treatments used, i . e ., sulfuric peroxide mixture, an ammonia peroxide mixture or ozonated water (DIO 3 ), DIO 3 exhibited the most effective Cl removal efficiency and surface roughness recovery. DIO 3 treatment successfully reduced the Cl-terminated Ru surface to its original state and decreased the surface roughness to the pre-Cl 2 -etched Ru value.
TL;DR: Mesure des proprietes des contacts electriques entre des metaux catalytiquement actifs (Pt, Rh and Ru) and des semiconducteurs presentant de l'interet pour les cellules photoelectrochimiques and les suspensions de particules (n-TiO 2, n-SrTiO 3, n-CdS and p-InP) utilisees for the decomposition photochimique de l-eau as mentioned in this paper.
Abstract: Mesure des proprietes des contacts electriques entre des metaux catalytiquement actifs (Pt, Rh et Ru) et des semiconducteurs presentant de l'interet pour les cellules photoelectrochimiques et les suspensions de particules (n-TiO 2 , n-SrTiO 3 , n-CdS et p-InP) utilisees pour la decomposition photochimique de l'eau. Donnees sur les phenomenes observes lors du degagement d'hydrogene et sur les mecanismes possibles
TL;DR: In this article, the effect of RuO2 is attributed to catalysis of hole transfer from the valence band of CdS to H2S or sulfide ion in solution.
Abstract: Illumination of US-dispersions by visible light in solutions containing H2S or sulfide ions leads to efficient generation of hydrogen and sulfur. Very small quantities of RuO2 deposited on the CdS-particles improve markedly the quantum yield of H2-formation for which the optimum value obtained so far is ϕ = 0.35 ± 0.1. The effect of RuO2 is attributed to catalysis of hole transfer from the valence band of CdS to H2S or sulfide in solution.
TL;DR: In this article, surface composition and depth profile studies of hemiplated thin film CdS:CuzS solar cells have been carried out using XPS and Auger electron spectroscopy (AES) techniques.
Abstract: Surface composition and depth profile studies of hemiplated thin film CdS:CuzS solar cells have been carried out using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) techniques. These studies indicate that the junction is fairly diffused in the as-prepared cell. However, heat treatment of the cell at 210°C in air relatively sharpens the junction and improves the cell performance. Using the Cu(2p3p)/S(2p) ratio as well as the Cu(LVV)/(LMM) Auger intensity ratio, it can be inferred that the nominal valency of copper in the layers above the junction is Cut and it is essentially in the CUSS form. Copper signals are observed from layers deep down in the cell. These seem to appear mostly from the grain boundary region. From the observed concentration of Cd, Cu and S in these deeper layers and the Cu(LVV)/(LMM) ratio it appears that the signals from copper essentially originate partly from copper in CuS and partly from Cu2t trapped in the lattice. It is significant to note that the nominal valence state of copper changes rather abruptly from Cut to Cuz+ across the junction.
TL;DR: In this article, it was shown that the microscopically discontinuous structure of the metal layer is responsible for the anomalous photovoltaic effect of metal-coated semiconductor electrodes.
Abstract: Metal-coated semiconductor electrodes such as Au/n-TiO 2 and Au/n-GaP show photovoltaic effect that cannot be explained by the conventional potential barrier model for metal—semiconductor contact. From experimental and theoretical investigations it has been concluded that the microscopically discontinuous structure of the metal layer is responsible for the anomalous photovoltaic effect. Several theoretical conclusions which are interesting from the point of view of solar energy conversion are derived. (1) Metal-coated semiconductor electrodes in electrolyte solutions generate high photovoltages at the metal—semiconductor interface in cases where the metal layer forms islands approximately 5 nm in diameter and separated by more than 20 nm from each other provided that the potential of the electrode is controlled so as to give band bending in the metal-free part of the surface. The maximum photovoltage can increase up to the equivalent of the band gap of the semiconductor in ideal cases. (2) The metal—semiconductor contact becomes ohmic when the potential of the electrode approaches the flat-band potential for the bare electrode in cases where the metal layer either has cracks or forms islands with gaps wider than 20 nm, say. Changes in the barrier height at the metal—semiconductor interface are not assumed in the theory, which can be applied to any metal—semiconductor pair. The conclusions provide a thoeretical basis for the explanation of the mechanisms of interesting properties of metal-coated semiconductor photoelectrodes and photocatalysts, such as enhanced hydrogen photoevolution on platinum-coated p-type semiconductor electrodes or on platinum-coated semiconductor particles in solution.