Surface Diffusion Distance of Bismuth Adatoms on Mica Surface

The mean distance of surface diffusion of bismuth adatoms on mica surface has been determined from the measurement of the sticking coefflcient and the nucleus density at the initial stages of vacuum deposition. For 593>T>413 K (T being the substrate temperature), the surface diffusion distance X was found to increase with decreasing temperature in accordance with the formula X=(1/2)a0exp {(Ea-Ed)/2RT} where a0 is the diffusion jump distance, Ea the adsorption energy and Ed the activation energy for surface diffusion. For 413>T>308 K, on the contrary, it was found that the diffusion distance decreased with decreasing temperature; this can be interpreted by the existence of residual gas molecules adsorbed on mica surface. Using the experimental values of the diffusion distance obtained in the temperature range above 413 K, where practically no adsorbed gas molecules remained on mica surface, the values of Ea–Ed and a0 have been estimated at 5.8 kcal mol-1 and 7.6 A, respectively.