Adsorption and Surface Diffusion of Copper on Tungsten

Abstract

The Cu/W adsorption system was studied by field-emission microscopy. Adsorption of one to ten atomic layers of Cu was followed through changes in the field-electron-emission pattern and average work function of the W field emitter. Surface diffusion was investigated for single-, double-, and triple-layer diffusion, and for successive diffusion of one layer of Cu on others up to four layers. The negative electric field used in some of the measurements was found to decrease the apparent activation energy and the pre-exponential factor of the diffusion equation. The activation energy varied over the tungsten surface, increasing with surface roughness; it also varied with coverage, decreasing rapidly at first and then slowly with increasing coverage. It is suggested that the limiting values of Q and D0 approximate the values for surface self-diffusion of Cu.