Title: Nanostructures from Heteroepitaxial Growth: Insights from Modeling and Multiple Scales Speaker: Mark Asta, Department of Chemical Engineering and Materials Science, UC DavisDate/Time: Thursday, July 6, 2006 10:00-11:00 am (MDT) Location: Building 980, Room 95 (Sandia NM), videoconferenced to 915/W133 (Sandia CA) Brief Abstract: Ge on Si(001) continues to receive widespread interest as a model system for detailed investigations of the mechanisms underlying quantum-dot self assembly in Stranski-Krastanov heterepitaxial growth. This talk will describe results of computational studies investigating the competing energetic factors governing the early stages of faceted-pyramid island formation in this system. In the hybrid computational approach employed, the results of first-principles surface-energy calculations are combined with continuum computations of elastic strain energies to model the formation energy of isolated pyramids as a function of size. The calculations point to pronounced effects on island stability associated with strain dependencies of the facet surface energies. The results also suggest that the excess energies associated with facet edges play a critical role in determining the size scale for island nuclei, a conclusion that is supported by direct atomistic calculations of the magnitude of these edge energies. We also describe the results of atomistic simulations showing the influence of elastic interactions between steps and vacancy lines upon the orientation dependence of the surface energy for small vicinal angles. Overall, the results illustrate the detailed nature of the insights that can be gained from combining modeling approaches across length scales in studying the driving forces for the formation of strained nanostructures.CSRI POC: Michael Parks, 845-0512 |