Investigation of condensation and evaporation of alkali halide crystals by molecular beam methods. XIV. Development of two-dimensional islands on the (100) surface of LiF

Abstract

The development of two-dimensional islands on the (100) surface of LiF is studied for temperatures T = 706−771 K and saturation ratios S = 1.9−13. From the dependence of the island size on the growth time the velocity of monatomic steps and with it the mean diffusion distance x s = a exp( E s 2kT ) = 3.7( 12 11 ) × 10 −8 exp[ (1.04 ± 0.15) eV 2kT ] cm is obtained. This result confirms the model of surface diffusion with jumps from one lattice site to a neighboring one. With earlier measured desorption times a surface diffusion coefficient D = 8.6 × 10 −3 exp( −0.32 kT ) cm 2 s −1 is obtained. The comparison of the experimental shape development of the islands with computer simulations of the island growth gives the relative strength of step to surface diffusion β ≈ 5.5(± 50%). Because of a strong scatter of the measurement points due to impediments of step movements caused by divalent cation impurities and adjacent steps, a temperature dependence of β cannot be determined.