Surface atomic structure of epitaxially grown erbium silicide films on Si(111)7×7

Abstract

The surface atomic structure of erbium silicide films epitaxially grown on Si(111)7\ifmmode\times\else\texttimes\fi{}7 by deposition in situ has been investigated by scanning tunneling microscopy (STM) and synchrotron radiation core-level photoelectron spectroscopy. For a film thickness of less than 1 ML, a silicide with a p(1\ifmmode\times\else\texttimes\fi{}1) low-energy electron-diffraction pattern is formed. Atomic resolution images reveal that this structure consists of a buckled Si double layer with atomic positions of the surface atoms very close to the ideal 1\ifmmode\times\else\texttimes\fi{}1 Si(111) surface. Thicker silicide films exhibit a ($\sqrt{3}$\ifmmode\times\else\texttimes\fi{}$\sqrt{3}$)R(30\ifmmode^\circ\else\textdegree\fi{}) superstructure usually attributed to an ordered network of Si vacancies. Atomic resolution STM images show that the surface termination for the bulk silicide also consists of a double-height Si layer where the superstructure is due to a small displacement of the upper Si atoms toward either T4 or H3 sites. As shown by core-level photoemission spectroscopy of the Si 2p peak as a function of the emission angle, the silicide does not show significant charge transfer within the surface layer. STM images directly exclude the presence of vacancies on the topmost Si layer.