Competition between terrace and step nucleation: epitaxy of CaF 2 on vicinal Si(111) studied by atomic force microscopy

Abstract

The morphology of CaF 2 adlayers deposited on vicinal Si(111) substrates has been studied by atomic force microscopy (AFM) for low and high deposition temperatures. In the low temperature regime the adlayer grows in the layer-by-layer growth mode preserving the vicinal step structure of the substrate. The diffusion energy of 1.5 eV for CaF 2 molecules on CaF 2 terraces is obtained from the transition from terrace to step nucleation. In the high temperature regime the adlayer morphology is very inhomogeneous since the adlayer grows in the Stranski–Krastanov growth mode. Here the CaF 2 growing on a closed CaF interface layer does not cover all terraces. This morphology is attributed to the heterogeneous nucleation of islands at steps and to the formation of additional triangular protrusions.