EPITAXIAL-GROWTH OF ALKALINE-EARTH FLUORIDES ON THE (001) SURFACE OF LITHIUM-FLUORIDE .2. THE SYSTEM CAF2 LIF(001)/

Epitaxial growth of CaF2 on the (0 0 1) surface of LiF is studied for crystal temperatures between 573 and 773 K and for molecular beam flux es of 1 x 10(12)-1 x 10(13) CaF2 molecules per cm(2) and s. For T = 57 3 K layer growth with the orientation CaF2(0 0 1)[1 0 0]parallel to Li F(0 0 1)[1 1 0] is found. The layer growth mode is interpreted by a re stricted mobility of CaF2 molecules at this low temperature. LEED stud ies suggest a rearrangement of the (0 0 1) plane of CaF2 leading to th e formation of nm-scaled fourfold pyramids with (1 1 1) facets or, alt ernatively, an ab initio formation of such pyramids accompanied by a f ast coalescence to a closed layer. For temperatures T greater than or equal to 673 K growth of islands occurs. With increasing temperature t he orientation changes to CaF2(0 0 1)[1 0 0]parallel to LiF(0 0 1)[1 0 0]. This latter orientation may be attributed to an increasing mixing of Li+ and Ca2+ ions, enforcing in this way a continuation of the cat ion arrangement of the underlying LiF crystal into the growing CaF2 is lands. As for MgF2/LiF(0 0 1), for the present system growth of LiF cr ystallites - presumably on already grown CaF2 layers - is found. The e pitaxial growth of these crystallites with the (1 1 1) surface paralle l to the original (0 0 1) surface of the LiF crystal is interpreted by a space filling arrangement of F- anions above Ca2+ ions.