Oxidation of Reduced Ceria by Incorporation of Hydrogen

The interaction of hydrogen with reduced ceria (CeO2‐x) powders and CeO2‐x(111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce3+ species to hydrogen, which results in the formation of Ce4+, and thus in oxidation of ceria

Oxidation of Reduced Ceria by Incorporation of Hydrogen

The interaction of hydrogen with reduced ceria (CeO2‐x) powders and CeO2‐x(111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce3+ species to hydrogen, which results in the formation of Ce4+, and thus in oxidation of ceria

Surface action spectroscopy with rare gas messenger atoms

Action spectroscopy with inert gas messengers is commonly used for the characterization of aggregates in the gas phase. The messengers, often rare gas atoms or D2 molecules, are attached to the gas phase aggregates at low temperature. Vibrational spectra of the aggregates are measured via detection of inert gas desorption following a vibrational excitation by variable-energy infrared light. We have constructed an apparatus for the application of action spectroscopy to surfaces of solids with the aim of establishing a new method for the vibrational spectroscopy of surfaces and deposited clusters. Experiments performed for neon covered V2O3(0001) show that this method can provide information about surface vibrations. Besides the surface sensitive channel, there is also a bulk sensitive one as demonstrated with the example of CeO2(111) thin film data. Unlike infrared reflection absorption spectroscopy, normalization to a reference spectrum is not required for action spectroscopy data, and unlike high resolution electron energy loss spectroscopy, the action spectroscopy method does not suffer from moderate resolution nor from multiple excitations. Selective decoration of specific surface features with messenger atoms may be utilized to focus the spectroscopic information onto these features

Vibrational action spectroscopy of solids: New surface-sensitive technique

Vibrational action spectroscopy employing infrared radiation from a freeelectron laser has been successfully used for many years to study the vibrational and structural properties of gas phase aggregates. Despite the high sensitivity of this method no relevant studies have yet been conducted for solid sample surfaces. We have set up an experiment for the application of this method to such targets, using infrared light from the freeelectron laser of the Fritz Haber Institute. In this paper we present first results of this technique with adsorbed argon and neon atoms as messengers. We were able to detect surface-located vibrations of a thin V2O3(0001) film on Au(111) as well as adsorbate vibrations demonstrating that this method is highly surface sensitive We consider that the dominant channel for desorption of the messenger atoms is direct inharmonic vibrational coupling, which is essentially insensitive to sub-surface or bulk vibrations. Another channel is thermal desorption due to sample heating by absorption of infrared light. The high surface sensitivity of the non-thermal channel and its insensitivity to sub-surface modes makes this technique an ideal tool for the study of surface-located vibrations Vibrational spectroscopy provides key information on surfaces and the interaction of adsorbed species with those surfaces. The most prominent examples are infrared reflection absorption spectroscopy (IRAS, for some early examples see ...[1-3]) and high-resolution electron energy loss spectroscopy (HREELS). .........[4] Both techniques exhibit considerable drawbacks In IRAS the intense instrumental contributions to the spectrum are removed via division by a reference sample spectrum, which has the consequence that an IRAS spectrum contains structures not only of the sample under consideration, but also of the reference sample, which can cause ambiguities ..