Ultrathin Alumina Films on Metallic Substrates: Structure and Metal Adsorption

Abstract

First principles density functional calculations are used to study the structure and properties of ultrathin films of alumina on Al(111) and Ru(0001) substrates. We focus on ≈5 Å two O-layer films, naturally produced by oxidizing NiAl, Ni₃Al, and Al deposited on Ru(0001). The interface consists of chemisorbed l×1 oxygen on the underlying metal [1], with a nearly coplanar layer of Al₂O₃ above. The lowest energy structure of the Al-sublattice is found to consist of zig-zag rows of octahedral and tetrahedral Al ions, resembling the bulk κ-phase. Eleven different adsorbed metals, spanning the periodic table, have been studied [2]. At low coverage the bond is purely ionic; at high coverage most metals bind principally by polarization. Contrary to speculations, isolated vacancies are found on MgO(100) not to directly promote metal nucleation [3], and we suggest this behavior is general. However, ad-OH is found not only to promote island nucleation, but can also, in high concentrations, produce wetting of alumina by Cu [4].