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 submon olayer reconstructions of the Pb/Ge(111) system have been studied with angle-resolved photoemission spectroscopy utilizing synchrotron radia tion. 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 th e adatom-induced surface states of the gamma and alpha phases have bee n probed along the GAMMAMBAR and GAMMAKMBAR directions of the surface Brillouin zone. Our results indicate that despite their structural dif ferences, the alpha and gamma phases have essentially the same electro nic structure. Comparisons are made between this system and prototypic al metal/Si(111)-(square-root 3 X square-root 3)R 30-degrees systems a nd with theory.