Thermal desorption and UPS study of CO adsorbed on Cu-covered Ru (0001)

We have studied the electronic structure and chemisorption properties of (0--4) monolayers of Cu evaporated on a Ru (0001) single crystal substrate. HeI UPS shows that the Cu d band initially (0--1.5 monolayers) forms as an asymmetric resonance of 0.75 eV half width, 2.75 eV below E/sub F/. When the Cu coverage is increased, the resonance broadens and shifts nearer E/sub F/ until a bulk (111) Cu spectrum is attained at 4.0 monolayers [Cu(111) forms on Ru(0001)]. Thermal desorption of CO from the Cu overlayers shows that CO is more strongly bound to the first layer of Cu(approx. =15 kcal/mol) than to the second and succeeding layers of Cu [approx. =12 kcal/mol typical of bulk (111) Cu]. There is also evidence that more CO adsorbs on the first layer of Cu than adsorbs on bulk (111) Cu