Epitaxial growth of CaF2 films on Si(111) studied by scanning tunneling microscopy

Using ultrahigh vacuum scanning tunneling microscopy, we have studied the early stages of the epitaxial growth of CaF2 films on Si( 1 1 1) at 630 degreesC at a slow deposition rate of 0.2 monolayer (EVIL) per minute. After formation of CaF interface layer, we observe the film grows in the sequence of step edge decoration. one-dimensional islands growth on the terrace, formation of clusters of the islands, coalescence of the island cluster and filling of gaps between the one-dimensional islands in the cluster and between the island clusters to complete a layer. By such a sequence, epitaxial CaF2 films with atomically flat surface could be grown in layer-by-layer fashion up to 3 ML. The growth mode is discussed in relation to kinetic phase diagram [M. 4. OImstead: Thin Filets: Heteroepituxial Svstems, eds. W. K. Liu and M. B. Santos (World Scientific. Singapore, 1999) Chap. 5].