ANGLE-RESOLVED PHOTOEMISSION-STUDY OF THE SUBMONOLAYER PHASES OF PB ON GE(111)

The (square-root 3 X square-root 3)R 30-degrees alpha and gamma submonolayer reconstructions of the Pb/Ge(111) system have been studied with angle-resolved photoemission spectroscopy utilizing synchrotron radiation. The alpha phase consists of 1/3 monolayer (ML) of Pb adatoms in T4 sites, whereas the gamma phase consists of an equal mix of Pb (1/6 ML) and Ge (1/6 ML) adatoms, forming a mosaic phase. Dispersions of the adatom-induced surface states of the gamma and alpha phases have been probed along the GAMMAMBAR and GAMMAKMBAR directions of the surface Brillouin zone. Our results indicate that despite their structural differences, the alpha and gamma phases have essentially the same electronic structure. Comparisons are made between this system and prototypical metal/Si(111)-(square-root 3 X square-root 3)R 30-degrees systems and with theory.