Speaker: Li Huang
Ames Laboratory of US DOE
Abstract: Surface diffusion plays a crucial role in a wealth of physical processes such as chemical reactions and catalysis, growth of crystals and thin films, and formation of nanostructures. So far, mass transport at surfaces is generally believed to process either (i) by single adatom jumping from one surface site to another or (ii) by cooperative processes involving simultaneous motion of two or more atoms. In this presentation, I will talk about atomistic processes involved in the homo-and heteroepitaxial growth of Si/Ge surfaces and the collective dynamics of Pb dense wetting layer on Si(111) systems.
Based on first-principles calculations of surface diffusion barriers, we show that on a compressive Ge(001) surface the diffusivity of Ge is 102–103 times higher than that of Si in the temperature range of 300 to 900 K, while on a tensile surface, the two diffusivities are comparable. Consequently, the growth of a compressive SiGe film is rather different from that of a tensile film. The diffusion disparity between Si and Ge is also greatly enhanced on the strained Ge islands compared to that on the Ge wetting layer on Si(001), explaining the experimental observation of Si enrichment in the wetting layer relative to that in the islands.
The dynamics of a dense Pb wetting layer on the Si(111) surface is studied in the framework of a generalized Frenkel-Kontorova model. Instead of the typical diffusion by random hopping processes, a liquidlike collective motion of the Pb atoms within the dense wetting layer is revealed to give rise to ultrafast kinetics of the wetting layer even at low temperatures. A kinetic Monte Carlo simulation including this collective spreading mechanism of the dense wetting layer quantitatively reproduces the experimental observations.
Date&Time: June 8, 2012 15:30 - 16:30
Location: 606 Conference Room
