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International audience; The formation of an ultra-thin aluminum oxide film at Fe0.85Al0.15(110) surface (A2 random alloy) has been studied by a variety of surface sensitive techniques (X-ray photoemission, low-energy electron diffraction, surface X-ray diffraction and scanning tunneling microscopy) supplemented by ab initio atomistic simulations. Since iron is not oxidized in the used conditions, the study focused on the coupling between aluminum oxidation and segregation processes. Compared to the bare surface, whose average composition (Fe0.6Al0.4) is closer to the B2-CsCl structure over a ∼ 3 nm depth, the oxidation hardly affects the subsurface segregation of aluminum. All the structural and chemical fingerprints point to an oxide film similar to that found on NiAl(110). It is a bilayer (∼ 7.5Å thick) with a composition close to Al10O13 and a large (18.8 × 10.7)Å 2 nearly rectangular unit cell; an almost perfect match between substrate periodicity and the (1 × 2) oxide supercell is found. Nevertheless, microscopy reveals the presence of anti-phase domain boundaries. Measured Al 2p and O 1s core level shifts match calculated ones; their origin and the relative contributions of initial/final state effects are discussed. The ubiquity of the present oxide on different supports asks for the origin of its stability.

International audience; The surface structure of Mg-doped rutile TiO 2 (011) surfaces is determined by combining core level/valence band photoemission and photoelectron diffraction (PED) to evolutionary algorithm, density functional theory (DFT) and multiple scattering calculations. Upon annealing the reduced crystal above 620 K, Mg segregates by substitution to Ti atoms from the TiO 2 lattice while keeping the known reconstruction of the Mg-free surface. Band gap states being totally healed by Mg segregation, the charge compensation is provided by O vacancies as formally expressed by the Kröger and Vink notation. A full support to those findings comes from

International audience; Based on previous photoemission findings, the influence of newly observed aluminum surface segregation at the low (110), (100) and (111) index surfaces of the A 2 body-centered Fe 0.85 Al 0.15 random alloy is explored. Scanning Tun-neling Microscopy, Low-Energy Electron Diffraction and Grazing-Incidence X-Ray Diffraction are combined to explore surface structures and topogra-phies. The formation of a surface composition close to the B 2 Fe 0.5 Al 0.5 occurs with the appearance of (i) a long-range pseudo-hexagonal incommen-surate superstructure with a periodicity of ∼ 18Å on the (110) surface, (ii) a (1 × 1) termination on the (100) surface and (iii) a intense vicinal faceting of the (111) surface in the form of triangular pits.

International audience; The configurations associated with reversible and irreversible adsorption of hydrogen on MgO escape consensus. Here, we report the dissociation of H2 on MgO nanocubes, which was examined by combining Fourier transform infrared spectroscopy and density functional theory (DFT)-based simulations. We found that the use of ultrahigh vacuum is essential for identifying the very first adsorption stages. Hydrogen pressure was varied from 10–8 mbar to near ambient, resulting in IR spectra of richer complexity than in current state of the art. Models with oxygen at regular corners (O3C) and Mg at inverse corners (MgIC) were identified to be the most reactive and to split H2 irreversibly already in the lowest pressure regime (PH2 < 10–3 mbar). The continuous increase in intensity of the corresponding IR bands (3712/1140 cm–1) in the intermediate range of pressures (10–3–1 mbar), along with the appearance of bands at 3605/1225 cm–1, was demonstrated to stem from cooperative adsorption mechanisms, which could be therefore considered as the main origin of irreversible hydrogen adsorption. At PH2 > 1 mbar, fully reversible adsorption was shown to occur at O4C (either on mono- or diatomic steps) and Mg3C sites. Another OH/MgH couple (3697/1030 cm–1) that became reinforced at high PH2 but remained stable upon pumping was correlated to O3C and MgIC in multiatomic steps. The difference in adsorption and desorption sequences confirmed the proposed cooperative adsorption of H2 molecules. Our study provides new insights into the mechanisms that can be beneficial for understanding the chemistry of H2 and other hydrogen-containing molecules, such as CH4, on oxide surfaces, but also for the advancement of hydrogen-storage technologies.

A coated metallic substrate and fabrication method The present invention relates to a coated metallic substrate comprising, at least; one layer of oxides, such layer being directly topped by an intermediate coating layer comprising Fe, Ni, Cr and Ti wherein the amount of Ti is above or equal to 5 wt.% and wherein the following equation is satisfied: 8 wt.% < Cr +Ti < 40 wt.%, the balance being Fe and Ni, such intermediate coating layer being directly topped by a coating layer being an anticorrosion metallic coating., La présente invention concerne un substrat métallique revêtu et un procédé de fabrication. La présente invention concerne un substrat métallique revêtu comprenant, au moins ; une couche d’oxydes, ladite couche étant directement surmontée d’une couche de revêtement intermédiaire comprenant Fe, Ni, Cr et Ti, la quantité de Ti étant supérieure ou égale à 5 % en poids et dans laquelle l’équation suivante est satisfaite : 8 % en poids < Cr +Ti < 40 % en poids, le reste étant Fe et Ni, une telle couche de revêtement intermédiaire étant directement surmontée d’une couche de revêtement qui est un revêtement métallique anticorrosion.