Surface states and reconstruction of epitaxial sqrt 3 x sqrt 3 R30 degrees Er silicide on Si(111).

Abstract

The surface electronic structure of epitaxial \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}3 R30\ifmmode^\circ\else\textdegree\fi{} ${\mathrm{ErSi}}_{1.7}$ 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 \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} M\ifmmode\bar\else\textasciimacron\fi{}, \ensuremath{\Gamma}\ifmmode\bar\else\textasciimacron\fi{} K\ifmmode\bar\else\textasciimacron\fi{}, and K\ifmmode\bar\else\textasciimacron\fi{} M\ifmmode\bar\else\textasciimacron\fi{} lines of the (1\ifmmode\times\else\texttimes\fi{}1) surface Brillouin zone. These data are compared to the band structure of two-dimensional p(1\ifmmode\times\else\texttimes\fi{}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\ifmmode\times\else\texttimes\fi{}1) surface-silicide bands folded back into the reduced \ensuremath{\surd}3 \ifmmode\times\else\texttimes\fi{} \ensuremath{\surd}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.