Fast Diffusive Behavior of Pb on Ge(111) at Low to Room Temperatures During Island Formation*

Lead deposited on Ge(111) at low temperatures (<260K) was found to show unusual collective diffusion behavior upon heating towards room temperature. As the sample was heated, Pb was seen diffusing from high coverage regions into a region of low Pb coverage, corresponding to islands forming from the wetting layer. Experiments studied the number density and island size as a function of coverage and temperature, as well as interaction with the electron beam, which was found to form regions with less Pb coverage. Eventually the regions of low coverage filled with enough Pb to form a uniform layer. Similar behavior was seen with Pb on Si(111) at low temperatures, with island formation whose heights were determined by quantum size effects,[1] as well as unusually fast diffusion speed.[2] In order to explain the diffusing behavior of Pb, we also present a first-principles study of the structure of Pb overlayers on Ge(111) using DFT calculations, which were inspired by experimental observations of Pb/Ge(111) phases.[3]
[1] M. Hupalo et al., Surf. Sci. 493, 526 (2001).
[2] M. Hupalo and M. C. Tringides, Phys. Rev. B 75, 235443 (2007).
[3] Y. Sato and S. Chiang, Surf. Sci. 603, 2300 (2009)