CO chemisorption on small cobalt particles deposited on Si(111)

"Island-like", highly dispersed, cobalt particles on a Si(111) single crystal have been prepared by means of an evaporation-sputtering technique. A unique electron structure of the Co islands measured by UPS, was developed. On adsorption of the CO molecules in l L dose a strong decrease in the density of states (DOS) of cobalt at 1.6 eV BE was observed which did not occur on a thick evaporated {Co}/{Si(111)} sample. Comparison of the photoemission spectra revealed the dissociation of the CO molecules as a prevailing process on small cobalt islands, whereas CO retains its molecular form on thick Co layers. Here UPS evidence is given for the chemical interaction between highly reactive Co and CO molecules as compared to that measured for thick {Co}/{Si(111)} and Si(111).