Diffusion kinetics of Bi and Pb–Bi monolayer precursing films on Cu(1 1 1)

We have used Auger electron spectroscopy to study the diffusive spreading and adsorption of pure Bi and Pb–11 at.%Bi precursing films on Cu(1 1 1) surfaces, from droplets of the respective materials. The Bi diffusion coefficient (DBi) increases with Bi-coverage. However, in the intermediate coverage range, DBi remains approximately constant, which is presumably due to the formation of an ordered Bi hexagonal overlayer. In the case of Pb–Bi alloy spreading, the presence of Bi slows down the Pb diffusion kinetics significantly. The kinetics of Bi spreading are also slower in the presence of Pb, but the effect is less marked. The equilibrium concentrations both at the Pb–Bi drop surface, and in the surrounding precursing film, were found to be Bi-enriched.