Experimental results from spectroscopic ellipsometry on the (7 X 7)SiO 11) surface reconstruction: dielectric function determination

Abstract

International audienceThe dielectric function of the (7 X 7) Si(l11) surface has been directly determined in UHV conditions by ellipso~etric measurements on a Si(111) clean surface. The dielectric function obtained from ellipsometric spectra near the pseudo-Brew-ster angle (PB) has been calculated by means of a three-phase model (bulk, (7 X 7) transition layer and vacuum) in which optical properties of bulk Si are deduced from literature data and the thickness of the (7 X 7) transition layer is taken from the DAS model. Our calculation allows us to confirm the metallic character of the (7 X 7) transition layer and to point out the previously found 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. This optical anisotropy is ascribed to some roughness anisotropy induced by steps