Copper wetting of alpha-Al2O3(0001): theory and experiment

X-ray photoelectron spectroscopy (XPS) studies have been carried out on spu tter deposited copper on a substantially hydroxylated alpha-Al2O3(0001) (sa pphire) surface under ultra-high vacuum (UHV) conditions. XPS-derived Cu up take curves show a sharp change in slope at a coverage of 0.35 ML (on a Cu/ O atomic basis), indicative of initial layer-by-layer growth. Cu(LMM) lines hape data indicate that, prior to the first break in the curve, Cu is oxidi zed to Cu(I). At higher coverages, metallic Cu(O) is observed. These data a gree with first principles theoretical calculations, indicating that the pr esence of adhydroxyl groups greatly enhances the binding of Cu to bulk sapp hire surfaces, stabilizing Cu(I) adatoms over two-dimensional metallic isla nds. In the absence of hydroxylation, calculations indicate significantly w eaker Cu binding to the bulk sapphire substrate and non-wetting. Calculatio ns also predict that at Cu coverages above 1/3 ML, Cu--Cu interactions pred ominate, leading to Cu(O) formation. These results are in excellent agreeme nt with experiment. The ability of surface hydroxyl groups to enhance bindi ng to alumina substrates suggests a reason for contradictory experimental r esults reported in the literature for Cu wetting of alumina. (C) 2000 Publi shed by Elsevier Science B.V. All rights reserved.