SYNCHROTRON-RADIATION PHOTOEMISSION-STUDY OF BA ON A SI(001)2 X-1 SURFACE

A synchrotron-radiation photoemission study of Ba deposited on a clean Si(001)2x1 surface at room temperature is presented. Upon Ba adsorpti on, the maximum drop in work function is about 2.3 eV. At submonolayer coverage, the asymmetric dimers on the surface are preserved. Near to one monolayer, however, they become symmetric. In the meantime, bariu m silicides start to form, first the monosilicide followed by the disi licide with increasing coverage. The Si 2p core-level photoemission sp ectra clearly exhibit these monosilicide and disilicide components hav ing a surface core-level shift of 1.05 and 1.84 eV, respectively.