Chemical state

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

The Role of Alloyed Molybdenum in the Dissolution and the Passivation of Nickel-Molybdenum Alloys in the Presence of Adsorbed Sulfur.

Abstract: The authors discuss the effects of Mo on the dissolution and the passivation of a Ni-2 atom percent (a/o) Mo(100) alloy in 0.05M H/sub 2/SO/sub 4/ investigated with or without adsorbed sulfur. Sulfur was preadsorbed on the alloy surface in H/sub 2/S-H/sub 2/ gas mixtures. Complete monolayers of S (i.e., 43 X 10/sup -9/ g/cm/sup 2/) were formed with pH/sub 2/ = 2 X 10/sup -4/ and T = 600{sup 0}C. The surface coverages by sulfur were measured using the sulfur 35 radioisotope (/sup 35/S) and the chemical state was analyzed by electron spectroscopy for chemical analysis. Potentiodynamic and potentiostatic measurements were performed, and the concentration of sulfur on the surface was measured as a function of the amount of dissolving molybdenum. The effect of S is found to be very weak compared to the one previously observed on Ni and Ni-Fe alloys, which shows that molybdenum counteracts the detrimental effects of adsorbed sulfur.

A Mössbauer study on remarkable changes in chemical states of iron in silica-supported Pd-Fe bimetallic catalysts by varying Fe contents

Abstract: Fe-57 Mossbauer spectra of silica-supported Pd−Fe bimetallic catalysts show remarkable changes with varying Fe/Pd atomic ratios. From the spectra, the main Fe-component is estimated as highly dispersed Fe in the Fe/Pd range of 0.05–0.3 and α-Fe ensemble and Fe−Pd intermetallics in the Fe/Pd range above 0.3. It is suggested that the chemical state of iron is associated with the catalytic performance in effective CO−H2 conversion to methanol.

Band structure and decay channels of thorium-229 low-lying isomeric state for ensemble of thorium atoms adsorbed on calcium fluoride

Abstract: The results are presented on the study of the electronic structure of thorium atoms adsorbed by the liquid atomic layer deposition from aqueous solution of thorium nitrate on the surface of CaF2. The chemical state of the atoms and the change of the band structure in the surface layers of Th/CaF2 system on CaF2 substrate were investigated by XPS and REELS techniques. It was found that REELS spectra for Th/CaF2 system include peaks in the region of low energy losses (3-7 eV) which are missing in the similar spectra for pure CaF2. It is concluded that the presence of the observed features in the REELS spectra is associated with the chemical state of thorium atoms and is caused by the presence of uncompensated chemical bonds at the Th/CaF2 interface, and, therefore, by the presence of unbound 6d- and 7s-electrons of thorium atoms. Assuming the equivalence of the electronic configuration of thorium-229 and thorium-232 atoms, an estimate was made on the time decay of the excited state of thorium-229 nuclei through the channel of the electron conversion. It was found that the relaxation time is about 40 {\mu}s for 6d-electrons, and about 1 {\mu}s for 7s-electrons.

Pt–CeO 2 Catalysts for Fuel Cell Applications: From Surface Science to Electrochemistry

Abstract: Nanostructured Pt–CeO 2 films with low Pt loading show high activity and stability as anode catalysts in proton-exchange membrane fuel cells Under electrochemical conditions, the noble metal in the catalyst films can be reversibly converted between two chemical states, an atomically dispersed Pt 2 + species and subnanometer Pt particles The nature of these states and the mechanism of their interconversion have been investigated combining surface science and electrochemical experiments The local structure of the Pt 2 + species, their stability, and reactivity were studied by means of synchrotron radiation photoelectron spectroscopy and resonant photoemission spectroscopy under ultrahigh vacuum conditions in combination with density functional modeling We employed surface science-based model systems of different complexity to probe the reactivity of the atomically dispersed Pt 2 + species in the absence of other species such as Pt 4 + , metallic Pt, or oxygen vacancies It was found that the conversion of Pt 2 + to subnanometer Pt particles is triggered by a redox coupling with Ce 3 + centers generated through the formation of oxygen vacancies or by charge transfer between the metal and the support These findings characterize the Pt–CeO 2 material as a structurally highly dynamic catalyst which attains its high stability from the ability to adapt to the changes in the operation conditions

Thermally Stimulated Desorption Measurements of Heavily Phosphorus-Doped Silicon Surfaces with a Very Thin Oxide Film

Abstract: Heavily phosphorus-doped silicon wafers were prepared by the Shiraki method as a chemical treatment. The thermally stimulated desorption (TSD) from these samples with thin oxide films was studied by using Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), and mass spectroscopy. The chemical states of the etched surfaces were measured by X-ray photoelectron spectroscopy (XPS). It was found that the thin oxide film on the doped polycrystalline Si surface was desorbed easily at relatively low temperature (560°C), similarly to a single-crystal one. The desorption of the oxide is due to the chemical state from the interface to the near-surface region which includes not only SiO2 but also SiOx. For a single-crystal silicon, a large quantity of phosphorus segregated to the near-surface region even after the oxide had desorbed. It is considered that this phosphorus segregation is attributable to the existence of the strain which is not relaxed because of the low annealing temperature even after desorption of the oxide.