Tensile Stress in Nanometre Thick MBE Grown CaF2 on (111) Si

CaF2 epitaxial layers were prepared by MBE and investigated by RBS and ion channeling measurements. Films of about 30 nm thickness were found to be strained by tensile stress causing a rhombohedral symmetry of the layers. These results are interpreted in terms of the different thermal expansion coefficients of substrate and deposit, respectively.