INFLUENCE OF THE MISMATCH DISLOCATIONS ON THE ELASTIC PROPERTIES OF THE INSULATING FLUORIDE FILMS DEPOSITED ON SI(111)

CaF2 and SrF2 films grown on Si(111) by molecular beam epitaxy were st udied by Brillouin spectoscopy method. The measured velocities of surf ace acoustic waves are in close agreement with those calculated within simple model of a layered structure. The only discrepancy was a decre ase of the velocity in CaF2 films of about 100 nn thick and was attrib uted to the different distribution of the defects arizing at the early stages of the growth modes at the beginning of CaF2 and SrF2 epitaxy on Si(111).