SURFACE PHASE-TRANSITIONS OF GE(111)C(2X8) STUDIED BY ELECTRON-ENERGY-LOSS SPECTROSCOPY

We report the results of an electron energy loss spectroscopy (EELS) i nvestigation of the Ge(111)c(2 x 8) surface at different temperatures, covering the three different phases previously observed for this syst em (c(2 x 8)[-](1 x 1)[-] surface premelting). In order to discriminat e between bulk and surface losses, we used different primary beam ener gies (50-500 eV). Four loss features are revealed to be affected by th e temperature. Results are discussed on the basis of a comparison with previous optical spectroscopy data and of the dielectric theory of EE LS applied to a slab geometry.