The dielectric function of the (7 x 7) Si(111) surface was directly determined in ultra-high vacuum conditions by ellipsometric measurements on a Si(111) clean surface. The dielectric function obtained from ellipsometric spectra near the pseudo-Brewster angle was calculated by means of a three-phase model (bulk, (7 x 7) transition layer and vacuum) in which optical properties of bulk Si were deduced from literature data and the thickness of the (7 x 7) transition layer was taken from the dimer–adatom–stacking-fault model. The calculation permitted confirmation of the metallic character of the (7 x 7) transition layer, and drew attention to previously found surface-state transitions at 2.6 and 3.4eV; and perhaps at 1.6eV. A surface-state transition was also confirmed at 3eV. Ellipsometric results depended upon the crystallographic direction, and were attributed to roughness anisotropy introduced by steps.

Experimental Results from Spectroscopic Ellipsometry on the (7 x 7)Si(111) Surface Reconstruction - Dielectric Function Determination. Z.Hammadi, M.Gauch, P.Müller, G.Quentel: Surface Science, 1995, 341[1-2], 202-12