Development of electronic band structure of the K-adsorbed Si(111)7 x 7 surface

Adsorption of K on the Si(111)7 x 7 surface has been investigated in the su bmonolayer coverage range at room temperature. The method of threshold phot oemission spectroscopy using s- and p-polarized light excitation was employ ed for studying the evolution of surface electronic structure near the Ferm i level, the work function and the ionization energy. A qualitative change in character of band structure has been observed, depending on K coverage. Suppression of metallicity of the Si(111)7 x 7 surface was found at the ini tial stage of K adsorption. One surface band Al below the VBM was revealed at low coverage. Increasing K coverage has led to both the appearance of th e K-induced band A(2) and significant movement of the band towards the Ferm i level. The K/Si(111)7 x 7 interface was found to be semiconducting-like u p to saturation coverage. Near saturation, the Fermi level is seen to cross the K-induced band A(2). Such surface band structure is identified as bein g metallic-like. Results indicate metallization via adlayer accompanied by Fermi level pinning.