EXPERIMENTAL RESULTS FROM SPECTROSCOPIC ELLIPSOMETRY ON THE (7X7)SI(111) SURFACE RECONSTRUCTION - DIELECTRIC FUNCTION DETERMINATION

The dielectric function of the (7 X 7) Si(111) surface has been direct ly determined in UHV conditions by ellipsometric measurements on a Si( 111) clean surface. The dielectric function obtained from ellipsometri c spectra near the pseudo-Brewster angle (PB) has been calculated by m eans of a three-phase model (bulk, (7 X 7) transition layer and vacuum ) in which optical properties of built Si are deduced from literature data and the thickness of the (7 X 7) transition layer is taken from t he DAS model. Our calculation allows us to confirm the metallic charac ter of the (7 X 7) transition layer and to point out the previously fo und surface-state transitions at 2.6 and 3.4 eV and perhaps at 1.6 eV. Furthermore, a surface-state transition has also been confirmed at 3 eV. Ellipsometric results depend on the crystallographic direction, Th is optical anisotropy is ascribed to some roughness anisotropy induced by steps.