Structure Analysis of the CaF2/Si(111) Interface in Its Initial Stage of Formation by Coaxial Impact-Collision Ion Scattering Spectroscopy (CAICISS)

Abstract

The structure of the CaF2/Si(111) interface in its initial stage of formation has been analyzed with a coaxial impact-collision ion scattering spectroscopy (CAICISS), in which an ion source and a time-of-flight energy analyzer are arranged coaxially so as to take the experimental scattering angle at 180°. It has been found that in the initial stage of the formation of the CaF2/Si(111) interface, a monolayer of CaF rather than CaF2 is formed on Si(111). The arrangement of the Ca and F atoms in the monolayer of CaF with reference to Si(111) is B-type, the Ca atoms being situated at the T4. site just above the second-layer Si atoms. The interlayer distance between the topmost F layer and the underlaying Ca layer is estimated to be 0.64 ± 0.05 A.