Ames Laboratory-USDOE and Department of Physics, Iowa State University, Ames Iowa 50011

The ability to manipulate atoms to form regular nano-structures through the self-assembly is a topic of much current interest. In metallic nano-structures, the quantum size effect has recently been recognized as a strong driving force for self-assembly of certain preferred sizes and geometry of metal islands in the deposition process. Instead of forming three-dimensional (3D) islands of various heights as commonly observed for nonreactive interfaces, under the right growth conditions the metal atoms can arrange themselves into plateaus or islands of selective heights, with flat tops and steep edges.  Recent experiment also showed that the kinetic behavior of coarsening and growth of Pb islands on Si(111) surface does not obey traditional classical kinetic model predictions. We have developed a novel theoretical model to describe this unconventional and rapid coarsening and growth behavior. In addition to the dependence of chemical potential on islands’ curvatures as in the classical coarsening model, our model incorporates the dependence of the chemical potential on the island height due to quantum size effects and also the effects of the dense wetting layer between the islands. Extensive first-principles calculations are performed to determine the relevant chemical potentials in the theory. Incorporating these features, this theoretical model predicts the evolutions of island density and height distribution in good agreement with experiments.

Work done in collaboration with Maozhi Li, J. W. Evans, M. Hupalo, M. C. Tringides, T. L. Chan, and K. M. Ho.