Surface structure of thin epitaxialCoSi2grown on Si(111)

Abstract

The surface structure of single-crystal, epitaxial, thin-film, ${\mathrm{CoSi}}_2$ on Si(111) substrates has been studied by low-energy electron diffraction, Auger-electron spectroscopy, Rutherford backscattering, and transmission electron microscopy. By controlling deposition and annealing parameters, the surface may be reversibly prepared with either of two stable structures which we call ‘‘${\mathrm{CoSi}}_2$-C’’ and ‘‘${\mathrm{CoSi}}_2$-S.’’ The ${\mathrm{CoSi}}_2$-C surface appears to be a bulk termination of the ${\mathrm{CoSi}}_2$ lattice with Si as the topmost layer. The ${\mathrm{CoSi}}_2$-S surface appears to be terminated by an additional bilayer of Si which allows full coordination for all Co and Si layers. A 2×2 superstructure is seen by low-energy electron diffraction during the transition from the ${\mathrm{CoSi}}_2$-C surface to the ${\mathrm{CoSi}}_2$-S surface. The orientation and stability of the additional bilayer of Si at the ${\mathrm{CoSi}}_2$-S surface may affect the orientation of epitaxial Si overlayers.