Variations in the nature of metal adsorption on ultrathin Al2O3 films

First-principles density-functional calculations are used to study metal ad sorption (Li, K, Y, Nb, Ru, Pd, Pt, Cu, Ag, Au, and Al at 1/3-4 monolayer c overages) atop 5 Angstrom Al2O3 films on Al(111). The oxide-metal bond is i onic at low coverages but, with interesting exceptions, caused by polarizat ion at high coverages where the overlayer is metallic. Binding trends are e xplained in terms of simple concepts. increasing overlayer thickness can ca use the adsorbate-oxide interface structure to change, and while some metal s wet, most do not.