Two-process diffusion of titanium on the (1 1 1) tungsten plane by the current fluctuation method in FEM

Abstract

Field emission current noise of titanium adsorbed on the (111) tungsten crystal face was investigated. Measurements were carried out for coverages ranging from 0.2 to approximately 2 monolayers in the temperature range 300–1500K. A linear combination of two theoretical functions obtained by Gesley and Swanson for the diffusion model of current fluctuations was fitted to the experimental autocorrelation functions. In such a way two diffusion coefficients and two activation energies for titanium surface diffusion were determined. The theoretical model is applicable to a temperature range of 800–1450K. The energy of each diffusion process decreases with increasing coverage, from a value of 1.77eV (the first process) and 1.42eV (the second process) until the saturation value of about 0.3eV is reached for both diffusion processes. The first process occurs below the phase transition point of titanium (1156K) and the second process occurs above it.