INVESTIGATION OF CONDENSATION AND EVAPORATION OF ALKALI-HALIDE CRYSTALS BY MOLECULAR-BEAM METHODS .14. DEVELOPMENT OF 2-DIMENSIONAL ISLANDSON THE (100)SURFACE OF LIF

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 v elocity of monatomic steps and with it the mean diffusion distance x(s ) = a exp(E(s)/2kT) = 3.7((12)(1.1)) x 10(-8) exp[(1.04 +/- 0.15)eV/2k T] cm is obtained. This result confirms the model of surface diffusion with jumps from one lattice site to a neighboring one. With earlier m easured desorption times a surface diffusion coefficient D = 8.6 x 10( -3)exp(-0.32/kT) cm(2) s(-1) is obtained. The comparison of the experi mental shape development of the islands with computer simulations of t he island growth gives the relative strength of step to surface diffus ion beta approximate to 5.5(+/- 50%). Because of a strong scatter of t he measurement points due to impediments of step movements caused by d ivalent cation impurities and adjacent steps, a temperature dependence of beta cannot be determined.