Chemical state

About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.

XPS studies of the thermal behaviour of passivated Zircaloy‐4 surfaces

Abstract: The composition and the chemical states of components of Zircaloy-4 (zirconium alloy) surfaces were studied in the temperature range between room temperature and 500°C. Each sample was kept at constant temperature (25, 100, 200, 300, 400, 500°C) for up to 16 hours. The changes of composition and chemical states of the Zircaloy-4 surface during heating were monitored by x-ray photoelectron spectroscopy (XPS). Originally, the components form well-defined layers elucidated by angle-resolved x-ray photoelectron spectroscopy (ARXPS). In contrast to depth profiling using ion sputtering, ARXPS is non-destrutive. However, it is applicable for layers of up to a few nanometres thickness only. The experiments showed a decomposition of the ZrO2 coverage above 200°C accompanied by oxygen diffusion into the bulk. These processes lead to the reduction of ZrO2 to metallic zirconium on the surface at 300°C and higher temperatures. The oxygen diffusion into the bulk was indicated by AES depth profiles. The layered structure observed up to a heating temperature of 200°C could not be seen at higher temperatures. After Zr metal appears at the surface during the heating process, a reaction with the adsorbed hydrocarbons takes place, leading to the formation of zirconium carbide. Though the depth resolution of an AES depth profile does not permit identification of layers with thicknesses in the nanometre region, the temperature-dependent behaviour of oxyen is reflected by its AES profiles, showing features in accordance with the results from ARXPS, especially with respect to the fact that well-defined layers vanish above 200°C.

Ligand field effect on the chemical shift in XANES spectra of Cu(II) compounds

Abstract: X-Ray absorption near-edge structure (XANES) spectra at the Cu L and K edges have been measured for a series of Cu(II) compounds to clarify the factor affecting the chemical shift in the XANES spectra. The energy positions of the 2p1/2 → 3d and 2p3/2 → 3d transition peaks in the Cu L2,3 XANES spectra and the 1s → 3d transition peak (pre-edge peak) in the Cu K-edge XANES spectra were strongly influenced by the chemical states of the Cu(II), i.e., the coordination geometries (tetrahedral, octahedral and square planar) and ligand electronegativity. In all the spectra, the peak position shifted to higher energy in the order of the spectrochemical series, and the shifts are explained in terms of the change in the ligand field splitting. It is proposed that chemical shifts in the 2p → 3d and 1s → 3d transitions can be attributed primarily to changes in the position of the unfilled Cu 3d level. The result demonstrates that chemical shifts in XANES spectra of Cu(II) compounds can be understood in terms of ligand field theory.

X‐ray photoelectron and Auger electron spectroscopic study of the CdTe surface resulting from various surface pretreatments: Correlation of photoelectrochemical and capacitance‐potential behavior with surface chemical composition

Abstract: The surface chemistry and stoichiometry of p‐ and n‐type CdTe photoelectrodes treated with oxidizing and reducing etches have been characterized by x‐ray photoelectron and Auger electron spectroscopies. The results of surface analysis have been correlated with the photoelectrochemical and capacitance–potential behavior of the photoelectrodes. ‘‘Oxidized’’ surfaces are covered by a thin Te0/TeO2 layer (or a thicker Te0 layer, if the etching procedure is slightly altered), resulting in Fermi level pinning: a constant photovoltage is found for a wide range of redox potentials and potential‐independent space charge layer capacitance obtains. ‘‘Reduced’’ surfaces closely resemble ion sputtered CdTe in chemical state and stoichiometry, resulting in more nearly ‘‘ideal’’ behavior: the semiconductor/electrolyte interface is rectifying in the dark; capacitance–potential behavior follows the Mott–Schottky equation near flat band conditions; and photovoltage varies with redox potential, from 0 to ∼0.7 V for p‐CdTe.