INTRINSIC VALENCE AND CONDUCTION BANDS OF SI(111)-1X1

The valence bands of the unreconstructed H-Si(111)-1x1 are investigate d using angle-resolved ultraviolet photoelectron spectroscopy. The hig h quality of the surface and the absence of reconstruction allow us to observe bulk bands comparable to theoretical calculations. The asymme tric dispersion of the valence bands along the <(M)over bar '> <(Gamma )over bar> (M) over bar direction of the surface Brillouin zone confir ms the asymmetry observed for the conduction bands. Such an asymmetry, stemming from the fact that the family of (11(2) over bar) planes are not mirror planes in the bulk of Si, provides a supplementary means o f disentangling bulk states from surface states.