Surface states and reconstruction of epitaxial √3 × √3 R30° Er silicide on Si(111)

The surface electronic structure of epitaxial √3 × √3 R30° ${\mathrm{ErSi}}_{1.7}$ 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 Γ¯ M¯, Γ¯ K¯, and K¯ M¯ lines of the (1×1) surface Brillouin zone. These data are compared to the band structure of two-dimensional p(1×1) 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(1×1) surface-silicide bands folded back into the reduced √3 × √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.