PHOTOEMISSION-STUDIES OF THE NA GE(111)-3X1 SURFACE/

The electronic structure of a Na/Ge(111)3 x 1 surface was investigated by valence-band and core-level photoemission spectroscopy with synchr otron radiation. The two-dimensional energy-band dispersion of the sur face Brillouin zone along (M) over bar-<(Gamma)over bar>-(K) over bar was mapped out. The experimental surface-state dispersions show a bett er agreement with the theoretical results for the buckled Seiwatz mode l than the extended Pandey model. The surface core-level shift of the (3 x 1) surface is explained on the basis of the buckled Seiwatz model . The (3 x 1) surface reveals more covalent bonding character than oth er Na-adsorbed surfaces at room temperature, and its surface Fermi lev el is close to the valence-band maximum.