Growth instabilities of CaF2 adlayers deposited at high temperature on Si(111)

The growth of ultrathin CaF2 films on Si(111) at high deposition temperature has been studied by UHV-atomic force microscopy (AFM) and by high-resolution low energy electron diffraction (SPA-LEED) during growth. The CaF2 film starts to grow in the step flow mode reproducing the Si substrate steps. The atomic force microscopy investigations show that after deposition of 2 TL CaF2 instabilities of the growing film lead to the formation of triangular islands on top of the initial CaF interlayer at these steps. These instabilities are enhanced with increasing 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 preferential nucleation centers.