Initial growth of CaF 2 and [formula omitted] on Si(110) during molecular beam epitaxy

Abstract

Reflection high-energy electron diffraction, scanning electron microscopy, atomic force microscopy and X-ray photo-electron spectroscopy were used to study the initial growth of CaF 2 on Si(110) and BaF 2 on CaF 2 Si(110) by molecular beam epitaxy. Growth of CaF 2 Si(110) initially proceeds two-dimensionally with a (1 × 3) surface reconstruction. The observation of core-level and Auger energy shifts for Ca and F peaks at low coverage suggests the presence of both CaSi and FSi bonds at the CaF 2 Si(110) interface. For higher coverages, [1̄10]-oriented ridges form and growth proceeds via the stacking of (111) and (111̄) planes on the sidewalls of the ridges. This ridged and grooved surface morphology is believed to result from the favorable energetics of exposing low-energy {111} facets and the formation of twinned crystallographic domains. Subsequent deposition of BaF 2 on CaF 2 Si(110) begins with incommensurate growth and nucleation on top of the CaF 2 ridges. Growth then continues on the sidewalls, resulting in recovery of the ridged and grooved morphology at higher coverages. Intermixing between the fluorides is believed to be negligible near the BaF 2 CaF 2(110) interface.