Applied Surface Science, Vol.252, No.15, 5300-5303, 2006
Hydrogen-induced metallization on Ge(111) xic(2 X 8)
We have studied hydrogen adsorption on the Ge(111) c(2 x 8) surface using scanning tunneling microscopy (STM) and angle-resolved photoelectron spectroscopy (ARPES). We find that atomic hydrogen preferentially adsorbs on rest atom sites. The neighbouring adatoms appear higher in STM images, which clearly indicates a charge transfer from the rest atom states to the adatom states. The surface states near the Fermi-level have been followed by ARPES as function of H exposure. Initially, there is strong emission from the rest atom states but no emission at the Fermi-level which confirms the semiconducting character of the c(2 x 8) surface. With increasing H exposure a structure develops in the close vicinity of the Fermi-level. The energy position clearly indicates a metallic character of the H-adsorbed surface. Since the only change in the STM images is the increased brightness of the adatoms neighbouring a H-terminated rest atom, we identify the emission at the Fermi-level with these adatom states. (c) 2005 Elsevier B.V. All rights reserved.
Keywords:scanning tunneling microscopy;angle-resolved photoelectron spectroscopy;hydrogen adsorption;Ge(111) c(2 X 8)