X-ray photoelectron spectroscopy, temperature-programmed desorption and temperature-programmed reduction study of LaNiO3 and La2NiO4 +? catalysts for methanol oxidation

Journal of Alloys and Compounds

et al. 2006

191

Epitaxial thin films of LaNiO 3−x were deposited by using a reactive d.c. magnetron sputtering technique. High-energy X-ray photoelectron spectroscopy was used to analyze the composition and valence states of La and Ni in the films after long time aging in atmosphere. The obtained results show the existence lanthanum and nickel in oxide and hydroxide chemical states. The oxygen exists in four chemical states: lattice oxides, hydroxyl groups and in adsorbed water. Comparison of the spectra recorded at normal emission and grazing emission angle revealed that the hydroxyl group's concentration is mostly present at the surface of the film.

Section: Resultsmentioning

confidence: 99%

Investigation of epitaxial LaNiO3−x thin films by high-energy XPS

Journal of Alloys and Compounds

et al. 2006

191

“…It is known that considerable segregation of elements takes place in chemically synthesized LaNiO 3−δ samples, i. e. the surface concentration of various species differs from the volume one [5]. Another factor to be considered is the tendency of rare earth and nickel oxides to absorb water vapour and carbon dioxide from air, so that any ex situ exposure of these films to air will result in an uncontrolled reaction and stoichiometry [6].…”

Section: Introductionmentioning

confidence: 99%

Surface stability of epitaxial LaNiO_3-δthin films

et al. 2010

Lithuanian J. Phys.

Thin LaNiO 3−δ films with pseudocubic (100) preferred orientation were prepared by reactive DC magnetron sputtering and in situ annealed in O2 and vacuum. X-ray photoelectron spectroscopy (XPS) was used to determine the variation in composition of the films under high temperature annealing. The experimental O 1s and La 3d -Ni 2p 3/2 spectra of LaNiO 3−δ films was analysed in terms of O 2− , O − /(OH) − , and weakly adsorbed oxygen species. It was shown that the change in the type of conductivity from metallic to semiconducting one is accompanied by a marked increase in the intensity of the lateral (∼531 eV) peak of oxygen. The quantitative analyses of La 3d -Ni 2p 3/2 spectra show that the Ni/La concentration ratio significantly decreases after heating above the dehydration temperature. These variations in conductivity and surface composition were attributed to the loss of lattice oxygen with subsequent adsorption of O − and (OH) − anions and weakly adsorbed oxygen species from ambient air.

“…It is known that a considerable surface segregation of elements may take place in LaNiO 3−δ samples [1]. Another factor to be considered is the tendency of rare earth and nickel oxides to absorb water vapour and carbon dioxide from air, so that any ex situ exposure of these films to air will result in an uncontrolled reaction and surface stoichiometry variation [2].…”

Section: Introductionmentioning

confidence: 99%

Resonant photoemission of LaNiO_3-δthin films

et al. 2010

Lithuanian J. Phys.

Thin LaNiO 3−δ films with pseudocubic (100) preferred orientation were prepared by reactive DC magnetron sputtering and annealed at ultra high vacuum above dehydration temperature. The resonant photoemission spectroscopy was used to study the surface composition and electronic structure under La 4d→4f and Ni 3p→3d photoexcitation. The resonance features observed in core level and valence band spectra under La 4d→4f transition were explained in terms of autoionization process and lanthanum-oxygen valence band states' hybridization. No resonant features were observed in the valence band spectra under Ni 3p→3d excitation indicating that nickel species are not present at the LaNiO 3−δ film surface after heat treatment.