Growth kinetics of CaF2/Si(111) for a two-step deposition

The growth of CaF2 on vicinal Si(111) substrates precovered by an interfaci al CaF layer was investigated using atomic force microscopy (AFM). The inte rfacial CaF layer is grown in a first deposition step at 750 degrees C, dep ositing 1.3 triple layers (TL's) CaF2. This is partially covered by CaF2 du e to the deposition of excess (>1 TL) CaF2. In a second step the succeeding CaF2 layers sue grown at lower temperatures (300-600 degrees C). The inhom ogeneous morphology of the initial film allows us to study simultaneously t he growth of CaF2 on the CaF interfacial layer and on CaF2 covered terraces formed during the first growth step. At low temperatures, the CaF2 growth on CaF2 tends to be layer-by-layer while the growth on the pure CaF layer i s dominated by three-dimensional islands. At temperatures above 500 degrees C, a transition from terrace to step nucleation is observed. These observa tions are explained using kinetic growth models to determine the diffusion barriers on both the CaF interfacial layer and the CaF2 islands.