INITIAL OXIDATION OF THE SC-ON-AL(111) SYSTEM, AS STUDIED BY PHOTOELECTRON-SPECTROSCOPY

A photoemission study of the initial oxidation of the Sc-on-Al(111) ov erlayer system is presented. Sc was deposited at room temperature on a n Al(111) substrate in the low coverage region (up to approximate to 3 0 Angstrom). A solid state reaction is considered to take place betwee n Sc and the topmost layer of the Al substrate. Oxygen exposures up to 100 L have been studied. The presence of Sc is found to increase the initial rate of oxidation of the Al substrate. The change in the work function of the system with oxygen exposure is found to be strongly de pendent on the amount of evaporated Sc. These findings are discussed i n terms of a simple model of formation of surface dipoles.