NEAR-FERMI LEVEL SURFACE-STATES INDUCED BY CS ADSORPTION ON THE SI(111)7X7 SURFACE

The electronic structure of the Si(111)7 X 7 surface modified due to C s-adsorption has been studied by means of a new method which uses the p- and s-polarized light excitation of threshold photoemission spectra . We found that the mechanism of interaction of polarized light with s urface states differs from that with bulk states. Photoemission from t he Cs-induced band was observed with the use of p-polarized light in t he absence of bulk photoemission. Based on this phenomenon, the fundam ental parameters of the Cs-band and the energy position of the Fermi l evel relative to both the vacuum and valence band maximum were obtaine d. The final pinning position of the Fermi level is found to be equal to 0.18 eV at a Cs coverage corresponding to the work function minimum . Metallization occurs due to Cs-coverage before the Fermi-level pinni ng.