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  Rudolph R. ; Pettenkofer C. ; Bostwick A.A. ; Adams J.A. ; Ohuchi F. ; Olmstead M.A. ; Jaeckel B. ; Klein A. ; Jaegermann W.: Electronic structure of the Si(1 1 1):GaSe van der Waals-like surface termination. New Journal of Physics 7 (2005), p. 108/1-20
  http://www.njp.org/

Abstract:
The electronic structure of the Si(111):GaSe surface termination has been determined using angle-resolved photoelectron spectroscopy using photons in the energy range 12-120 eV supplied by BESSY and ALS. Thje electronic structure resembles those of the layered chalcogenide GaSe and is discussed in relation to this. The chemical bond between the Si and Ga surface atoms is non-polar and therefore similar to the Ga-Ga bond in GaSe single crystals and also to the Si-Si bond in bulk silicon. The latter explains the absence of a surface core level shift in Si 2p photoelectron spectra of the terminated surface