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) investigation of the Ge(111)c(2 x 8) surface at different temperatures, covering the three different phases previously observed for this system (c(2 x 8)[-](1 x 1)[-] surface premelting). In order to discriminate between bulk and surface losses, we used different primary beam energies (50-500 eV). Four loss features are revealed to be affected by the temperature. Results are discussed on the basis of a comparison with previous optical spectroscopy data and of the dielectric theory of EELS applied to a slab geometry.