Inhomogeneous growth of CaF2 adlayers on Si(111) at intermediate temperatures

The growth morphology of CaF2 adlayers deposited in the temperature range 500–650°C on Si(111) samples with 0.9° miscut in View the MathML source direction has been studied by atomic force microscopy (AFM). After transferring the samples from the MBE chamber to ambient air we found an inhomogeneous film morphology: on one hand there are smooth islands wetting substrate terraces and on the other hand different substrate terraces show small clusters. The cluster formation is attributed to the reaction of the first unstable CaF2 layer after contact with ambient air while the smooth areas consist of thickness stabilized CaF2 islands. The smooth islands grow preferentially in the View the MathML source direction since the substrate steps block the growth in View the MathML source direction.