SURFACE-STATES AND RECONSTRUCTION OF EPITAXIAL ROOT-3-X-ROOT-3R 30-DEGREES ER SILICIDE ON SI(111)

The surface electronic structure of epitaxial root 3 X root 3R 30 degrees ErSi1.7 layers on Si(111) has been studied by high-resolution angle-resolved ultraviolet photoemission spectroscopy. Typical surface states or resonances are unambiguously identified and their band dispersions mapped along the high-symmetry Gamma ($) over bar M ($) over bar Gamma ($) over bar K ($) over bar, and K ($) over bar M ($) over bar lines of the (1 X 1) surface Brillouin zone. These data are compared to the band structure of two-dimensional p(1 X 1) Er silicide extensively studied in previous works. It is found that the prominent surface bands observed in the 0-3-eV binding-energy range can be readily derived from the p(1 X 1) surface-silicide bands folded back into the reduced root 3 X root 3 zone. This indicates that the bulk silicide is also terminated with a buckled Si layer without vacancies, quite similar to the surface-silicide termination. In particular, specific surface bands reflect the doubly (essentially) occupied dangling bonds and the back bonds of the buckled Si top layer.