RESUMO
We considered the effect of coverage of the surface of In2O3 films with rhodium on the sensitivity of their electrophysical properties to ozone (1 ppm). The surface coverage with rhodium varied in the range of 0-0.1 ML. The In2O3 films deposited by spray pyrolysis had a thickness of 40-50 nm. The sensor response to ozone depends on the degree of rhodium coverage. This dependence has a pronounced maximum at a coverage of ~0.01 ML of Rh. An explanation is given for this effect. It is concluded that the observed changes are associated with the transition from the atomically dispersed state of rhodium to a 3D cluster state.
RESUMO
Combining experimental spectroscopy and hybrid density functional theory calculations, we show that the incorporation of fluoride ions into a prototypical reducible oxide surface, namely, ceria(111), can induce a variety of nontrivial changes to the local electronic structure, beyond the expected increase in the number of Ce3+ ions. Our resonant photoemission spectroscopy results reveal new states above, within, and below the valence band, which are unique to the presence of fluoride ions at the surface. With the help of hybrid density functional calculations, we show that the different states arise from fluoride ions in different atomic layers in the near surface region. In particular, we identify a structure in which a fluoride ion substitutes for an oxygen ion at the surface, with a second fluoride ion on top of a surface Ce4+ ion giving rise to F 2p states which overlap the top of the O 2p band. The nature of this adsorbate F--Ce4+ resonant enhancement feature suggests that this bond is at least partially covalent. Our results demonstrate the versatility of anion doping as a potential means of tuning the valence band electronic structure of ceria.
RESUMO
We have deposited two monolayers of Sn onto Rh(111) single crystal. After the deposition, no ordered structure was revealed by low energy electron diffraction (LEED). We oxidized the obtained system in a low-pressure oxygen atmosphere at 420 K. The oxidized sample was then gradually heated to study the thermal stability of the oxide layer. We characterized the system by synchrotron radiation stimulated photoelectron spectroscopy and LEED. Valence band and core level photoelectron spectra of rhodium, tin and oxygen were used to study the oxidation of the Sn-Rh(111) surface and its behaviour upon annealing. A low stoichiometric oxide of Sn was created on the surface. The oxidation process did not continue towards creation of SnO(2) with higher oxygen dose. The annealing at 970 K caused decomposition of the surface oxide of Sn and creation of an ordered (â3 × â3)R30° Sn-Rh(111) surface alloy.
RESUMO
Non-evaporable Ti-Zr-V ternary getters (NEGs) were studied by means of excitation energy resolved photoelectron spectroscopy (ERXPS). We attempted a quantitative study of the in-depth redistribution of the NEG components during activation. The samples were prepared ex-situ by DC magnetron sputtering on a stainless-steel substrate. The ERXPS measurements were carried out at two incident photoelectron beam angles at energies of 110, 195, 251, 312, 397 and 641 eV. Besides these photon energies, also standard X-ray photoelectron spectroscopy (XPS) was used at a photon energy of 1254 eV. We accumulated Ti 3s, Ti 3p, Ti 3d, V 3s, V 3p, V 3d, Zr 3p, Zr 3d, Zr 4s, Zr 4p, Zr 4d, C 1s, O 1s and O 2s photoelectron peak intensities as functions of the kinetic energies given to them. Under simplifying assumptions, Monte-Carlo calculations of the activated sample concentration profiles were performed to fit the measured spectra intensities. The results proved an in-depth redistribution of the components during the activation process. This way we also contributed to a further development of non-destructive depth profiling by electron spectroscopy techniques.
