GROWTH INSTABILITIES OF CAF2 ADLAYERS DEPOSITED AT HIGH-TEMPERATURE ON SI(111)

The growth of ultrathin CaF2 films on Si(111) at high deposition tempe rature has been studied by UHV-atomic force microscopy (AFM) and by hi gh-resolution low energy electron diffraction (SPA-LEED) during growth . The CaF2 film starts to grow in the step flow mode reproducing the S i substrate steps. The atomic force microscopy investigations show tha t after deposition of 2 TL CaF2 instabilities of the growing film lead to the formation of triangular islands on top of the initial CaF inte rlayer at these steps. These instabilities are enhanced with increasin g CaF2 coverage so that the CaF2 him forms wedges with extremely large flat terraces separated by steps that are some nm high. Additionally, small three-dimensional islands nucleate at these steps acting as pre ferential nucleation centers.