Surface states on Si(111)-(2×1)

Abstract

Surface-state energy bands for a single-domain Si(111)-(2\ifmmode\times\else\texttimes\fi{}1) surface have been studied with angle-resolved photoemission using synchrotron radiation. From the angular photoelectron distributions seen with a display-type spectrometer, we conclude that there are two surface states near the top of the valence bands ${E}_{v}$, one at ${E}_{v}\ensuremath{-}0.7$ eV around $\overline{\ensuremath{\Gamma}}$[0.65 eV full width half maximum (FWHM)] and a second at ${E}_{v}\ensuremath{-}0.15$ eV (0.4 eV FWHM) along the line $\overline{J}\overline{K}$. These states are found to be nearly dispersionless along the symmetry lines $\stackrel{-}{\ensuremath{\Gamma}{J}^{\ensuremath{'}}}$ and $\overline{J}\overline{K}$. Their range of existence can be related to different gaps in the projected bulk bands. The lower surface state lies in a band gap above the ${L}_{3}$ point which we find at ${E}_{v}\ensuremath{-}1.5$ eV. Our findings are not well described by band calculations reported to date which use buckled-surface model geometries. Our results also indicate that several discrepancies among different reported experimental results are likely due to multidomain cleavage effects. We conclude that either the geometry of Si(111)-(2\ifmmode\times\else\texttimes\fi{}1) has not yet been determined unambiguously or that the surface states cannot be described by a bandlike model which is the basis of present calculations.