EPITAXIAL-GROWTH OF ALKALINE-EARTH FLUORIDES ON THE (001) SURFACE OF LITHIUM-FLUORIDE .1. THE SYSTEM MGF2 LIF(001)/

Epitaxial growth of MgF2 on the (0 0 1) surface of LiF crystals is stu died for crystal temperatures T = 700-762 K and for molecular beam flu xes of 7.6 x 10(13)-6.0 x 10(14) MgF2 molecules/(cm(2) s). MgF2 grows mainly in the form of needle-like crystallites whose axes correspond t o the c-axis of this tetragonal rutile structure type. The orientation s MgF2(1 0 0)[0 0 1]parallel to LiF(0 0 1)[<(1)over bar 1 0>] and MgF2 (1 1 0)[0 0 1]parallel to LiF(0 0 1)[<(1)over bar 1 0>] are found to p revail. Besides growth of MgF2 also non-oriented growth of lithium flu oride crystallites is observed. The growth of LiF crystallites may be explained by an increase of the activity of the lithium fluoride cryst al by incorporation of Mg2+ ions into the crystal lattice and by the e xistence of adsorption sites with a higher binding energy at MgF2 clus ters on or in the outermost surface layer of the LiF crystal.