Submonolayer Sodium Coverage of the Si–SiO2 Interface

Abstract

It is well known that fractional monolayers of sodium can be electrolytically deposited on the Si–SiO2 interface, but the resulting electronic structure has not been fully determined. We present thermionic emission and photoemission measurements of uniformly coated interfaces which clearly show a reduction of the contact barrier due to an interface dipole layer. The photoelectric threshold, determined by the photoyield corrected for optical absorption Y/α, is reduced by sodium to a saturation value of 2.6 eV at a full monolayer coverage. This is consistent with the thermionic emission results which show an electronic barrier of 2.7 eV at the full monolayer coverage. A simple mathematical model is given to explain this dipole layer.