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 adsorption, 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, barium silicides start to form, first the monosilicide followed by the disilicide with increasing coverage. The Si 2p core-level photoemission spectra clearly exhibit these monosilicide and disilicide components having a surface core-level shift of 1.05 and 1.84 eV, respectively.