Vacuum evaporation of thin alumina layers

International audienc

Abilities of elastic peak electron spectroscopy in the field of thin films growth investigation: Au on Al and Al2O3

International audienc

Cogelation: an effective sol-gel method to produce sinter-proof finely dispersed metal catalysts supported on highly porous oxides

peer reviewe

Morphology and CO Oxidation Reactions on Anion Doped CeO_XF_Y/Rh(111) and CeO_X/Rh(111) Inverse Catalysts

Doping cerium oxide with additives is a common procedure that improves stability of cerium oxide-based catalysts. We prepared fluorine-doped cerium oxide samples in the form of inverse catalysts on Rh(111) and compared their electronic, chemical, and morphological properties with fluorine-free CeO_X samples. By means of X-ray photoelectron spectroscopy (XPS), we followed the formation of oxygen vacancies and the depletion of fluorine after exposure of CeO_XF_Y to CO and O₂ gases at elevated temperatures. According to Ce 3d XPS spectra, the ability to create oxygen vacancies is not altered by fluorine atoms. Our results from low energy electron diffraction (LEED) and atomic force microscopy (AFM) show that fluorine affects mainly the morphology of the layers. Unlike the CeO₂ layers, fluorine-doped samples form 3D islands, which are partially rotated with respect to Rh [11̅0] direction due to stretching of the lattice constant caused by cerium oxide reduction. The possibility for creation stable Ce³⁺ sites without reducing the oxygen storage capacity makes anion doping a perspective tool for defect engineering in cerium oxide-based catalysts

Bimetallic Nickel–Cobalt Nanosized Layers Supported on Polar ZnO Surfaces: Metal–Support Interaction and Alloy Effects Studied by Synchrotron Radiation X-ray Photoelectron Spectroscopy

The interaction of ultrathin bimetallic Ni–Co layers (0.25 and 1.5 nm) supported on polar (0001)­Zn–ZnO and (0001̅)­O–ZnO substrates was investigated by synchrotron-based photoelectron spectroscopy (PES) under ultrahigh vacuum (UHV) and O₂ environments. Monometallic Ni and Co layers were also characterized to highlight the influence of Ni–Co synergetic effects on the metal–support interaction. At room temperature, cobalt is partially oxidized, while nickel is metallic. The effect of ZnO surface termination is minor, while the influence of surface hydroxyl groups is discussed. Annealing at 773 K in UHV promotes oxidation of monometallic Ni and Co layers but has little influence on bimetallic Ni–Co. In addition, significant agglomeration of the Ni–Co overlayer is observed, with a parallel increase in the surface Co concentration. Agglomeration of Ni–Co is more pronounced on O-terminated ZnO. Upon annealing in 1 × 10^–6 mbar of O₂, both Ni and Co readily oxidize and redisperse over the ZnO substrate. Moreover, cobalt tends to segregate over nickel, creating a concentration gradient between the two alloy constituents (probably a core–shell-like structure). Overall, our results indicate that the interaction at the Ni–Co/ZnO interface is influenced by the synergetic effects between the two metals and to a lesser extent by the substrate termination. Taking into account the substantial progress made in the synthesis of ZnO nanostructures and surfaces, this study can assist in the effort toward improved ZnO-based catalysts with tailored properties