Photoemission study of the Si(111)6 x 1-Cs surface.

Abstract

We report results of a photoemission study, using synchrotron uv and x-ray radiation, for Cs adsorption on the clean Si(111)7\ifmmode\times\else\texttimes\fi{}7 surface at an elevated temperature with an emphasis on the Si(111)6\ifmmode\times\else\texttimes\fi{}1-Cs surface. From the analysis of the Cs 4d and Si 2p core-level spectra, we find that even at 540 \ifmmode^\circ\else\textdegree\fi{}C Cs atoms are adsorbed at adatom and rest atom sites at the initial stage, and successive deposition of Cs induces a reconstruction of the substrate to the 6\ifmmode\times\else\texttimes\fi{}1 phase via 3\ifmmode\times\else\texttimes\fi{}1. In the case of the 6\ifmmode\times\else\texttimes\fi{}1 surface there are two surface components, ${\mathit{S}}_{1}^{\ensuremath{'}}$ and ${\mathit{S}}_{2}^{\ensuremath{'}}$, originated from the Si bonded to Cs atoms and the unbonded Si atoms, respectively. The saturation Cs coverage of the 6\ifmmode\times\else\texttimes\fi{}1 surface is estimated to be 2/3 ML. We have also observed a surface state ${\mathit{SS}}_{1}^{\ensuremath{'}}$ at about 0.49 eV below the Fermi edge in the valence band and the semiconducting nature of the 6\ifmmode\times\else\texttimes\fi{}1 surface. The physical implications of these experimental observations are discussed within the framework of the previously proposed structural models.