The structure of sodium adsorbed c(2 × 8)Ge(111) surface

Abstract We performed SEXAFS and core level photoemission studies of Na adsorbed on c(2 × 8)-Ge(111) surface at different coverage regimes. The c(2 × 8) LEED pattern of the clean Ge(111) surface changes to a (1 × 1) with higher background after Na adsorption. A plasmon feature appears on the low energy side of Na 2p core level which indicates metallization of the Na overlayer. We determined the NaGe bond length from the SEXAFS data using the theoretical phase shift of NaGe, calculated by FEFF program. SEXAFS model calculations show that Na atoms are adsorbed on threefold-coordinated hollow sites with a NaGe bond length of 2.9 A and a second nearest neighbour distance of 3.4 A to the Ge atoms in the second layer.