Highlights Surface Science Lab

The knowledge of the atomic positions at metal-oxide junctions is a prerequisite for the rational design of ultrathin oxide films. The determination of atomic arrangement at the interfaces is a key feature for the use of oxide coatings as protective layers and for tuning the electronic properties of the oxide supported active metal clusters, which is a very important issue in order to engineer new catalysts. However, the breaking of the bulk periodicity often results in a large atomic rearrangement, confined within few Å from the interface, which is extremely difficult to characterize experimentally. Because of the large lattice mismatch, the periodic structural modifications extend laterally over few nanometers, thus strongly limiting the applicability of diffraction techniques based on long-range order due to the large dimensions of the unit cells. The possibility to separate nonequivalent chemical species in x-ray photoelectron diffraction measurements allowed us to unveil a large modification of the alumina ultrathin epitaxial oxide film grown on Ni3Al (111).

In order to determine the alumina structure we have compared the experimental photoelectron diffraction modulation functions of chemically nonequivalent Al and O species with multiple-scattering simulations.The remarkable outcome of this study is the ejection of the alloy first-layer Al atoms towards the ultrathin oxide layer.
Our findings provide the evidence for the formation of a new Al intermediate metallic layer at the metal-oxide interface. The formation of this new interface structure is crucial for the explanation of several properties of the aluminum oxide films.

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Large Interlayer Relaxation at a Metal-Oxide Interface:The Case of a Supported Ultrathin Alumina Film;
Erik Vesselli, Alessandro Baraldi, Silvano Lizzit, and Giovanni Comelli
Phys. Rev. Lett. 105, 046102 (2011).