COADSORPTION OF CU AND O2 ON A RU(0001) SURFACE

The adsorption behavior of oxygen on Cu submonolayer, monolayer and multilayer films epitaxially grown on a Ru(0001) substrate is studied by AES, LEED, TDS and delta-phi-measurements. In the presence of coadsorbed oxygen and below 500 K the Cu films preserve a layered structure. In the case of theta(Cu) < 1 ML the interaction is dominated by the free Ru(0001) sites. Annealing of the Cu film after adsorption of oxygen destabilizes the Cu structure and Cu clusters are formed; the O atoms are then distributed among the free Ru areas and the Cu clusters. Up to approximately 6 ML the adsorption of oxygen is influenced by the presence of the underlying Ru(0001) substrate, possibly in two ways: (a) by direct mutual influence between both metals and (b) by the presence of relatively high oxygen concentration within the thin Cu films (Ru acts at this temperature as diffusion barrier for oxygen). The adsorption is accompanied by diffusion into the Cu overlayer as evidenced by a comparison of AES and TDS data for theta(Cu) greater-than-or-equal-to 6 ML.