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Zhaochi Feng - One of the best experts on this subject based on the ideXlab platform.
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Relation between the Photocatalytic and Photoelectrocatalytic Performance for the Particulate Semiconductor-Based Photoconversion Systems with Surface Phase Junction Structure
The Journal of Physical Chemistry C, 2015Co-Authors: Xiang Wang, Shaoqing Jin, Xiuli Wang, Zhaochi FengAbstract:Although the Surface Phase junction can efficiently boost photocatalytic (PC) reactions, its role in photoelectrocatalytic (PEC) reactions has not been well-understood yet. In this study, we investigated the effect of the Surface Phase junction on the PEC performance of photoelectrodes fabricated with Ga2O3 and TiO2 particles. The Surface Phase junctions beneficial for PC reactions show a negative effect on PEC performance, which is mainly due to the significant influence of charge transportation between semiconductor particles by the Surface Phase junction. Photogenerated charge separation is promoted by the Surface Phase junction for both PC and PEC reactions, but the much more severe interfacial recombination occurs in the PEC reaction when charge carriers migrate across semiconductor particles to reach a conducting substrate. The opposite effects of the Surface Phase junction on PC and PEC performance reported here indicates that the fabrication of a heterojunction or Phase junction in the right struc...
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Surface Phase Composition of Iron Molybdate Catalysts Studied by UV Raman Spectroscopy
The Journal of Physical Chemistry C, 2008Co-Authors: Guoqing Jia, Jing Zhang, Zhaochi FengAbstract:Catalytic performance depends largely on the Surface properties. Here, the Surface Phase composition of iron molybdate catalysts with different Mo/Fe atomic ratios calcined at different temperatures was studied by UV Raman spectroscopy. In this study, the Surface enrichment of MoO3 that the Mo-rich catalysts undergo during calcination treatment is revealed by the increase in the Raman intensity of MoO3. X-ray photoelectron spectroscopy (XPS) analysis provides further evidence that the concentration of Mo increases evidently with increasing calcination temperature. The Surface enrichment of MoO3 also results in a significant variation of the morphologic appearance as evidenced by the presence of a needle-like material assigned to MoO3 on the Surface, while the Surface Phase composition remains almost unchangeable for the sample with a stoichiometric atomic ratio. These results are attributable to the formation of a substitution structure of Fe3+ ions in an octahedral coordination by Mo6+ ions in Mo-rich ca...
Mireille Privat - One of the best experts on this subject based on the ideXlab platform.
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Polyethylene Glycol Adsorption on Silica: From Bulk Phase Behavior to Surface Phase Diagram
Langmuir, 2007Co-Authors: Nawal Derkaoui, René Olier, Sylvère Said, Yves Grohens, Mireille PrivatAbstract:A characterization of the bulk-Phase diagram from literature data and new NMR and DSC measurements provided us with valuable elements that are helpful for gaining, from aqueous solution, better insight into the Surface behavior of polyethylene glycol on Aerosil 200. Adsorption isotherms built further to measurements by a depletion method showed a strong and temperature-dependent variation of the isotherm shape in agreement with the variations of interactions already evidenced in the bulk. In temperature−concentration areas, where water is behaving as a helix-promoting solvent, the finding of positive PEG adsorptions and stairlike isotherms agrees with observations reported in the literature. We identified some of the vertical parts as corresponding to the formation of monolayers of helix-shaped PEG molecules. In poor-solvent zones, adsorptions were null or negative, and the isotherms exhibited oscillations suggesting very different Surface behavior. Our data analysis evidenced the presence of a much greater amount of water than in the previous Surface states; however, the similar analysis of PEG behavior remains relevant. Indeed, the occurrence of first-order transitions in the Surface layer implies some water reorganization, permitting the PEG molecules to move closer to the Surface and become helix-shaped to rearrange in a monolayer. The Surface Phase diagram confirmed this analysis in a very satisfying way.
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Surface Phase Transitions at Liquid-Mixture/Solid Interfaces
Langmuir, 1999Co-Authors: Isabelle Mazeas, Pascal Pélerin, Hamid Sellami, Ahmed Hamraoui, René Olier, Mireille PrivatAbstract:In an adsorption study from a liquid mixture, the choice of a moderately hydrophilic silica and of a solute like 2,5-dimethylpyridine (2,5-DMP), known for its layering ability in dilute solution in water, allows the observation of several adsorption gaps on the isotherms established at different temperatures. These gaps may be attributed to Surface Phase transitions. Collected on a (T−Γ21) diagram, they constitute a Surface Phase diagram highly similar to the bulk water−2,5 DMP liquid−solid diagram at low temperature. It is the first example of a Surface Phase diagram at a liquid-mixture/solid interface.
V.g. Lifshits - One of the best experts on this subject based on the ideXlab platform.
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The formation of Si(1 1 1)5 × 2-Au single-domain Surface Phase by a Surface diffusion
Applied Surface Science, 2004Co-Authors: D.a. Tsukanov, Serguei V. Ryjkov, O. A. Utas, V.g. LifshitsAbstract:Abstract Using low energy electron diffraction (LEED) and the four-point probe method for measurements of electrical conductivity in situ the formation of the single-domain Si(1 1 1)5 × 2–Au Surface Phase has been studied. This Surface Phase is formed by Surface diffusion of gold atoms from a gold strip with thickness of about 10 monolayers. The changes in Surface conductivity for Si(1 1 1)5 × 2–Au single-domain Surface Phase are evaluated in comparison with the Si(1 1 1)5 × 2–Au three-domain Surface Phase formed by deposition of 0.5 monolayers of Au and subsequent annealing.
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a Surface Phase with a variable composition
Surface Science, 2000Co-Authors: Alexander A. Saranin, V.g. Lifshits, Andrey V. Zotov, Osamu Kubo, T. Harada, Mitsuhiro Katayama, Kenjiro OuraAbstract:Abstract Using scanning tunneling microscopy, the changes in the morphology and atomic structure of the Si(111)5 3 ×5 3 -Sb Surface during Sb desorption have been studied. It has been found that the Si(111)5 3 ×5 3 -Sb Surface Phase does not have a definite composition. In attempting to explain the 5 3 ×5 3 long-range order stability in a wide Si and Sb coverage range it has been suggested that Sb atoms partially substitute for the boundary Si dimers in the basic 5×5 dimer–adatom–stacking-fault structure. A possible model of the Si(111)5 3 ×5 3 -Sb reconstruction satisfying this requirement has been proposed.
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The role of Si atoms in In/Si(111) Surface Phase formation
Surface Science, 1998Co-Authors: Alexander A. Saranin, V.g. Lifshits, Andrey V. Zotov, Osamu Kubo, Mitsuhiro Katayama, Toshinori Numata, H. Tani, Kenjiro OuraAbstract:Abstract The deposition of In onto the Surface appears to result, depending on the temperature, in the formation of three different reconstructions, Si(111)-(2 × 2)-In (20–100°C), Si(111)-(4 × 1)-In (∼200°C) and (∼450°C). The formation of each Surface Phase has been determined to be controlled by the mobility of the top Si atoms. At the to (2 × 2) transition, the bulk-like termination of the Si(111) substrate is preserved. At the formation of the Si(111)-(4 × 1)-In Phase, Si atoms reorder via a bond-switching process. The formation of the Phase involves Surface Si mass transport. The applicability of the results obtained to other submonolayer adsorbate/Si systems is discussed, and the criterion for revealing the Surface Phases with a reconstructed substrate is formulated.
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Si overgrowth on Si(111)√3 × √3-B Surface Phase
Surface Science, 1996Co-Authors: Andrey V. Zotov, V.g. Lifshits, M. A. Kulakov, S.v. Ryzhkov, B. Bullemer, Ignaz EiseleAbstract:Abstract Si(111)√3 × √3-B Surface Phase has been formed by high-temperature annealing of B-doped Si samples. Low-energy electron diffraction observations have revealed that the Si(111)√3 × √3-B Surface Phase is very stable with respect to heating and that the √3 × √3 reconstruction is still detected at temperature as high as 950°C. Scanning tunnelling microscopy has been used to study the growth of Si on Si(111)√3 × √3-B Surface. At low temperatures (20–300°C) the growth has been found to be affected greatly by Surface defects which trap Si atoms and act as sites of preferential island nucleation. At temperatures of Si(111) epitaxy (≥ 400°C) Si islands grow amorphous up to a certain critical size and then “crystallize” to form epitaxial islands with a thickness of two Si(111) bilayers. The structure on top of epitaxial Si islands is always √3 × √3 which suggests boron segregation to the Surface.
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Thin gold and indium films on Si(111) Surface
Surface Science, 1992Co-Authors: O.v. Bekhtereva, B.k. Churusov, V.g. LifshitsAbstract:Abstract A 3-component system (AuInSi) and thin indium and gold film interactions on the Si(111)7 × 7 Surface were examined using Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). A new Surface Phase Si (111)3 × 1-( Au , In ) was detected at submonolayer metal coverages. Gold and indium were deposited under UHV conditions with further annealing at 300–500°C. It was shown that the agglomeration of gold atoms into islands covered by indium atoms takes place upon deposition of In onto the Si(111)5 × 1-Au Surface Phase with further annealing. This explains the absence of the gold Auger-peak (69 eV). Indium atoms in excess with respect to the Si(111)1 × 1-In Surface Phase are responsible for the SiAu Surface Phase decay and for the formation of gold islands covered by indium.
I. Eisele - One of the best experts on this subject based on the ideXlab platform.
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Formation and silicon overgrowth of √3 × √3-R30° boron Surface Phases on Si(111)
Materials Science and Technology, 2002Co-Authors: T Stimpel, Harry E. Hoster, J. Schulze, H. Baumgärtner, I. EiseleAbstract:AbstractIt is well known that boron (B) forms Surface Phases if deposited on Si Surfaces. One interesting Phase is the so called √3 × √3-R30° boron Surface Phase (BSP) on Si(111). This Surface Phase is different from all other √3 × √3-R30° Surface reconstructions formed by group III atoms because B alone is able to induce this reconstruction in two different configurations. Few facts are known about the step by step formation of this √3 × √3-R30° BSP and its Si overgrowth, although this is particularly important for the incorporation of BSPs into novel electronic devices. Therefore, the formation of the Surface Phase by in situ scanning tunnelling microscopy (STM) has been investigated. Examination showed that deposition of B led to the breakdown of the 7 × 7 reconstruction and to the formation of a Si Surface with a BSP located on T4 lattice sites (B-T4). Thermal annealing of the structure causes the B atoms to migrate from T4 to S5 positions. The two Phases exhibit completely different properties as a r...
Jacques Jupille - One of the best experts on this subject based on the ideXlab platform.
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Surface termination of hematite at environmental oxygen pressures experimental Surface Phase diagram
Physical Review B, 2007Co-Authors: A. Barbier, N Kasper, M J Guittet, Andrea Stierle, Jacques JupilleAbstract:We provide an experimental Surface Phase diagram (Surface termination versus chemical oxygen potential) of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Fe}}_{2}{\mathrm{O}}_{3}(0001)$ using a natural single crystal Surface. In a partial reduction reoxidation cycle, we observe a sequence from oxygen-, to ferryl-, and again oxygen-terminated Surfaces, in better agreement with recent density functional theory in the generalized gradient approximation calculations than with calculations taking into account on-site $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}3d$ Coulomb repulsion. The nonreversible change in Surface termination is accompanied by the formation of basal twins, which act as a sink for the extra Fe ions during the Surface transformation processes.
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Surface termination of hematite at environmental oxygen pressures: Experimental Surface Phase diagram
Physical Review B: Condensed Matter and Materials Physics, 2007Co-Authors: A. Barbier, N Kasper, M J Guittet, Andrea Stierle, Jacques JupilleAbstract:We provide an experimental Surface Phase diagram (Surface termination versus chemical oxygen potential) of alpha-Fe2O3(0001) using a natural single crystal Surface. In a partial reduction reoxidation cycle, we observe a sequence from oxygen-, to ferryl-, and again oxygen-terminated Surfaces, in better agreement with recent density functional theory in the generalized gradient approximation calculations than with calculations taking into account on-site Fe 3d Coulomb repulsion. The nonreversible change in Surface termination is accompanied by the formation of basal twins, which act as a sink for the extra Fe ions during the Surface transformation processes.
