SURFACE AND INTERFACE PROPERTIES FOR THE CU/W(110) SYSTEM AND THEIR EFFECT ON OXYGEN-ADSORPTION

The results of angle-resolved ultraviolet photoemission measurements and electronic-structure calculations are presented for Cu adsorbed on the W(110) surface. Data as a function of Cu coverage suggest the existence of sets of surface and interface states resulting from the Cu-W interaction. Calculations corroborate this suggestion and identify the surface and interface character and orbital symmetries of the states. Near the zone boundary along the GAMMABAR-HBAR symmetry line, these states lie in gaps in the projected bulk band structure for the W(110) surface and are localized either within the Cu overlayer (surface states) or shared between the Cu and first W layer (interface states). Reasonable agreement is obtained between experiment and theory. We also performed low-energy electron diffraction and measured the behavior of the surface and interface states with O2 coverage. We conclude that the enhancement of the O2 dissociative sticking coefficient for the 1-monolayer Cu film results from an increase in the precursor-state accommodation coupled with the ability of Cu to displace easily giving O2 continued access to the more active W surface.