0000000000352151
AUTHOR
P. Lagarde
Tetrahedral versus octahedral Mn site coordination in wurtzite and rocksalt Zn1−xMnxO investigated by means of XAS experiments under high pressure
Abstract We present the results of x-ray absorption measurements carried out in Zn 1− x Mn x O thin films under high pressure. The Mn environment remains essentially the same for nominal Mn concentrations given by x = 0.05 , 0.1, 0.15 and 0.25. Both the XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) indicate that Mn occupies the Zn site, being surrounded by four oxygen atoms at 2.02±0.01 A. The substitutional hypothesis is reinforced by comparing the differences between the ambient (wurtzite) and high pressure (rocksalt) spectra, which correspond to tetrahedral and octahedral Mn environments.
Sodium Adsorption on the TiO2110 Surface an XAFS Structural Study
The adsorption site of sodium atoms deposited onto a clean TiO2(110) surface has been determined by EXAFS. The best result is obtained for an 'in-between' site where the sodium is bound to two bridging oxygen atoms at 2.25 A and one in-plane one at 2.40 A in full agreement with DFT calculations. At higher coverage the site becomes a hollow site where Na is equidistant to the three oxygen atoms at 2.30 A.
The defined adsorption site of sodium on the TiO2(110)–(1×1) surface
The adsorption site of sodium on the TiO2(1 1 0)–(1 × 1) surface was studied by extended X-ray absorption fine structure. For coverage ranging between 0.25 and 0.5 ML, we find that sodium is on an ‘in-between' site where it is bound to two bridging oxygen atoms at 2.25 Å and one in-plane oxygen atom at 2.40 Å, in full agreement with DFT calculations. At higher coverage the site becomes an hollow site where the sodium atom is equidistant to the three oxygen atoms at 2.30 Å, while metallic sodium clusters are also formed at the surface.
Interfacial reaction between deposited molybdenum and TiO2(110) surface: role of the substrate bulk stoichiometry
Abstract The interfacial reaction between deposited molybdenum and three different TiO2(1 1 0) substrates (a bulk and surface stoichiometric TiO2; a bulk stoichiometric and surface reduced crystal; a bulk and surface slightly reduced crystal) was investigated by means of X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge spectroscopy (XANES). While the interfacial reaction is not a function of the substrate at room temperature (in any case, molybdenum layers grow with oxygen dissolved in), this study clearly reveals a strong effect of the substrate bulk stoichiometry on the chemical state of the deposit after annealing up to 750 °C whereas the substrate surface stoichiome…