Epitaxial growth of alkaline earth fluorides on the (0 0 1) surface of lithium fluoride .3. The system BaF2/LiF(O O 1) - epitaxial growth of LiBaF3

The development of overlayers during the interaction of molecular beams of BaF2 with (0 0 1) surfaces of LiF is studied for crystal temperatures 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 strongly, and growth of BaF2 in the orientation BaF2(0 0 1)[1 0 0]parallel to LiF(0 0 1)[1 1 0] with a misfit m = + 8.8% occurs only as a transient and altogether negligible phenomenon. Growth of LiBaF3 proceeds in the orientation with parallel axes, i.e. with LiBaF3(0 0 1)[1 0 0]parallel 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-dimensional islands is found. The formation of closed layers can be accelerated 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 thicknesses can be grown. By evaporation of LiF onto already grown LiBaF3 layers, epitaxial growth of LiF in an orientation corresponding to that of the underlying LiF crystal is found. Closed LiF layers are achieved for T = 573 K and j(on)(LiF) = 1 x 10(12) cm(-2) s(-1) at a thickness of approximate to 30 nm. This would, in principle, enable the fabrication of superlattices LiF/LiBaF3/LiF etc. with layer thicknesses suitable for optical applications.