INITIAL GROWTH OF CAF2 AND BAF2 CAF2 ON SI(110) DURING MOLECULAR-BEAMEPITAXY/

Reflection high-energy electron diffraction, scanning electron microsc opy, atomic force microscopy and X-ray photoelectron spectroscopy were used to study the initial growth of CaF2 on Si(110) and BaF2 on CaF2/ Si(110) by molecular beam epitaxy. Growth of CaF2/Si(110) initially pr oceeds two-dimensionally with a (1 x 3) surface reconstruction. The ob servation 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 CaF2/Si(110) interface. For higher coverages, [<(1)over bar 10>]-orie nted ridges form and growth proceeds via the stacking of (111) and (11 (1) over bar) planes on the sidewalls of the ridges. This ridged and g rooved surface morphology is believed to result from the favorable ene rgetics of exposing low-energy {111} facets and the formation of twinn ed crystallographic domains. Subsequent deposition of BaF2 on CaF2/Si( 110) begins with incommensurate growth and nucleation on top of the Ca F2 ridges. Growth then continues on the sidewalls, resulting in recove ry of the ridged and grooved morphology at higher coverages. Intermixi ng between the fluorides is believed to be negligible near the BaF2/Ca F2(110) interface.