CaF2 and SrF2 films grown on Si(111) by molecular beam epitaxy were st
udied by the Brillouin spectoscopy method. The measured velocities of
surface acoustic waves are in close agreement with those calculated wi
th a simple model of a layered structure. The only discrepancy was a d
ecrease of the velocity in CaF2 films of about 100 nm thick: this was
attributed to the difference of the growth modes at the beginning of C
aF2 and SrF2 epitaxy on Si(111).