The properties of CO and K co-adsorbed on Ni(111), studied by thermal desorption and metastable quenching spectroscopy

Abstract

We use thermal desorption and metastable quenching spectroscopy to study the (CO+K)/Ni(111) system. We find that CO and K co‐adsorption increases the binding energy (to the surface) of both molecules; that at coverages of more than one potassium atom per, roughly, eight nickel atoms the adsorbed CO molecules exchange atoms; that this exchange takes place without formation of a detectable (by MQS) number of adsorbed carbon and oxygen atoms; that the 2π* peak in the Penning spectrum is enhanced by the presence of the potassium; that at high potassium coverages CO and K desorb at practically the same temperature giving rise to a very narrow thermal desorption peak. We discuss the spectroscopic evidence concerning the detection of the 2π* orbital. We suggest that our experiments indicate that at low potassium coverage the surface has two local work functions: one corresponds to Ni atoms unmodified by the presence of potassium, and the other to strongly modified, low work function sites.