Growth kinetics ofCaF2/Si(111)for a two-step deposition

Abstract

The growth of ${\mathrm{CaF}}_{2}$ on vicinal Si(111) substrates precovered by an interfacial CaF layer was investigated using atomic force microscopy (AFM). The interfacial CaF layer is grown in a first deposition step at $750\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ depositing 1.3 triple layers (TL's) ${\mathrm{CaF}}_{2}.$ This is partially covered by ${\mathrm{CaF}}_{2}$ due to the deposition of excess $(>1\mathrm{TL})$ ${\mathrm{CaF}}_{2}.$ In a second step the succeeding ${\mathrm{CaF}}_{2}$ layers are grown at lower temperatures $(300--600\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}).$ The inhomogeneous morphology of the initial film allows us to study simultaneously the growth of ${\mathrm{CaF}}_{2}$ on the CaF interfacial layer and on ${\mathrm{CaF}}_{2}$ covered terraces formed during the first growth step. At low temperatures, the ${\mathrm{CaF}}_{2}$ growth on ${\mathrm{CaF}}_{2}$ tends to be layer-by-layer while the growth on the pure CaF layer is dominated by three-dimensional islands. At temperatures above $500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ a transition from terrace to step nucleation is observed. These observations are explained using kinetic growth models to determine the diffusion barriers on both the CaF interfacial layer and the ${\mathrm{CaF}}_{2}$ islands.