Abstract
New experimental evidence supporting the surface-defect models for thermally cleaned Si(111) surfaces is presented. Photoemission spectral intensities for the two distinct surface states at 0.8 and 2.0 eV below Fermi level change dramatically, depending on detailed thermal preparation procedures. This implies different geometries and is correlated with the reactivity of H chemisorption. The enhancement of the defect-induced state at 2 eV on the quenched metastable surface and the formation of the trihydride phase suggest that vacancy-type defects can easily be incorporated on the Si(111) surface by thermal treatments.