Real-time in situ spectroscopic ellipsometry and in situ, angle-resolved x-ray photoelectron spectroscopy (AR-XPS) have been applied to establish the relationships between the growth kinetics and the developing microstructure of ultrathin (<3 nm) oxide films grown on clean Al–1.12 at. % Mg alloy surfaces by thermal oxidation in the temperature range T=300–485 K. To this end, procedures for the depth-resolved quantitative AR-XPS analysis of ultrathin, multiple-element, and/or multiphase oxide overgrowths on binary alloy surfaces were developed. As a result, the relationships between the relative depth distributions of Al and Mg in the developing oxide films, the oxide-film growth kinetics, and the oxidation-induced compositional changes in the AlMg alloy substrate could be established as a function of the oxidation conditions.
The microstructural evolution of ultrathin (<3 nm) oxide films grown on bare Al-based AlMg alloy substrates, by thermal oxidation in the temperature range of 300 to 610 K and at partial oxygen pressures in the range 10 À4 -10 À2 Pa, was investigated by high-resolution transmission electron microscopy. Angle-resolved x-ray photoelectron spectroscopy was applied to establish the chemical constitution of the analyzed oxide films (i.e., the overall Al/Mg cationic ratio, as well as the relative depth distributions of Al and Mg in the grown oxide films). The $0.8-nm-thick (Al,Mg)-oxide film grown at 300 K is fully amorphous. A gradual development of long-range order in the oxide film sets in for thickening (Al,Mg)-oxide films of relatively high Mg content at T ! 475 K. The amorphous-to-crystalline transition proceeds by a phase separation: still predominantly amorphous oxide regions exist next to crystallized oxide regions, which are constituted of an MgO-type of oxide phase with a face-centered-cubic oxygen sublattice and an average lattice parameter of 4.146 AE 0.1 Å .
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