ANISOTROPY IN SURFACE DIFFUSION OF POTASSIUM ON THE W(112) REGION

Abstract
Measurements of anisotropic surface diffusion of potassium submonolayers on the (112) region of tungsten were carried out using a special version of the field emission fluctuation method. A rectangular slit was used as a probe hole which could be rotated in situ. The mean square fluctuations for successive slit positions were measured and the corresponding values of the diffusion coefficient were calculated by using theoretical results obtained recently by Gesley and Swanson. Activation energies were calculated from the temperature dependence of the diffusion coefficient determined in the temperature range between 395 and 490 K. High anisotropy in the surface diffusion coefficient was found at lower temperatures and also its decrease with increasing temperature. Surface diffusion along the [111] direction is much faster than along the [101] direction. This can be explained by the anisotropy of the substrate atomic structure. The ratio A=D[111]/D[110] is about 10 at 400 K but only 1.5 at 490 K. The subscripts indicate cristallographic directions on the W(112) plane.