EPITAXIAL-GROWTH OF ALKALINE-EARTH FLUORIDES ON THE (001) SURFACE OF LITHIUM-FLUORIDE .3. THE SYSTEM BAF2 LIF(OO1) - EPITAXIAL-GROWTH OF LIBAF3/

The development of overlayers during the interaction of molecular beam s of BaF2 with (0 0 1) surfaces of LiF is studied for crystal temperat ures T = 573-673 K and for impinging BaF2 fluxes j(on) = 1 x 10(12)-1. 5 x 10(13) cm(-2) s(-1). As long as the LiF supply from the substrate is not hindered formation and epitaxial growth of LiBaF3 dominates str ongly, and growth of BaF2 in the orientation BaF2(0 0 1)[1 0 0]paralle l to LiF(0 0 1)[1 1 0] with a misfit m = + 8.8% occurs only as a trans ient and altogether negligible phenomenon. Growth of LiBaF3 proceeds i n the orientation with parallel axes, i.e. with LiBaF3(0 0 1)[1 0 0]pa rallel to LiF(0 0 1)[1 0 0], with a misfit m = -0.82%. As growth mode, island growth with nucleation, growth and coalescence of three-dimens ional islands is found. The formation of closed layers can be accelera ted by decreasing the crystal temperature or increasing the impinging molecular beam flux. With a BaF2 flux only, layer thicknesses, because of the necessary supply of LIF from the substrate, are limited, while with congruent LiF and BaF2 fluxes, layers of virtually unlimited thi cknesses can be grown. By evaporation of LiF onto already grown LiBaF3 layers, epitaxial growth of LiF in an orientation corresponding to th at of the underlying LiF crystal is found. Closed LiF layers are achie ved for T = 573 K and j(on)(LiF) = 1 x 10(12) cm(-2) s(-1) at a thickn ess of approximate to 30 nm. This would, in principle, enable the fabr ication of superlattices LiF/LiBaF3/LiF etc. with layer thicknesses su itable for optical applications.