Chemical state

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

Interaction of tungsten with CeO2(111) layers as a function of temperature: a photoelectron spectroscopy study.

Abstract: The interaction of tungsten with CeO2(111) layers grown on Cu(111) was studied in the temperature range between 300 and 870?K by photoelectron spectroscopy of the core levels and resonant valence band spectroscopy. The interaction was found to be very strong even at 300?K, leading to the formation of cerium tungstate Ce6WO12 in which the metal atoms were in Ce3 + and W6 + chemical states. The growth was limited by the diffusion of W atoms into the ceria layer, so subsequent tungsten deposition led to formation of W suboxides with consecutively lower chemical oxidation states, i.e.? W4 + , W2 + and metallic W0 with an almost negligible contribution of W5 + . Step-wise annealing of the layer showed that due to stimulated diffusion of tungsten into ceria at higher temperature, Ce6WO12 was formed more easily. Larger W overlayer thicknesses needed higher annealing temperature to promote diffusion. The thickest sample studied, 1.4?nm W/CeO2, was transformed by annealing to 870?K to the Ce6WO12/W system with a tungsten monoxide (WO) interface, whereas the rest of the tungsten was converted to the W6 + oxidation state.

XPS studies on passivated and degraded YBa2Cu3O7−x films

Abstract: High-temperature YBa 2 Cu 3 O 7 − x superconductors are known to degrade in the presence of moisture. It was shown that the use of certain polymeric materials in solution during processing of the superconductor could passivate the film and reduce degradation in the macroscopic scale. X-ray photoelectron spectroscopy was used to study the surfaces of passivated as well as degraded YBa 2 Cu 3 O 7 − x samples. In the degraded sample, Y, Ba, Cu and O were present in chemical states other than those expected in superconductors. Segregation of Ba at the surface was also observed. In the passivated sample, superconducting species were retained at the surface despite limited impurity build-up.

Photoelectron spectra of condensed gases on an inert substrate

Abstract: There have been numerous attempts to use ultraviolet photoemission spectroscopy (UPS) to monitor the chemical states of adsorbed gas molecules on metal surfaces. To interpret the data correctly, one has to determine the effect of photoemission on the measured energy levels of the molecule. We have measured the UPS spectra of seven gases (C6H6, C5H5N, CH3OH, C2H5OH, H2CO, H2O, NH3) condensed on a LN2 cooled MoS2 substrate at hν = 21.2 eV. The inertness of the MoS2 substrate assures that no strong chemical bonding exists between the substrate and adsorbed molecules. For each gas, the spectrum of the condensed phase is similar to the corresponding spectrum of the gas phase except all the energy levels are shifted up by the same amount. This shift ranges from 1 to 1.65 eV for the gases studied. The energy shift is attributed to the dielectric screening of the hole produced during the optical excitation.

Hydrogen in perovskites: Mechanism of solubility, chemical state, effect on electron subsystem, phase transformation

Abstract: The phenomena of hydrogen/water solubility in YBa2Cu3O7-δ and BaCeO3 undoped and doped by Y and Nd are considered. New experimental data as well as recently published data have been accumulated to discuss the chemical state of protons, taking into account the fairly strong interaction of the protons with the electron subsystem. Phase transformation of the studied oxides induced by hydrogen/water intercalation were revealed by the investigations of thermal effects, X-ray diffraction, Raman spectroscopy, inelastic neutron scattering and nuclear quadrupole resonance.