surface

1. edge bulk surface total NIRT: The Evolution and Self-Assembly of Quantum DotsP. W. Voorhees, A. Golovin, M. Asta, M. Miksis and S. Davis, Northwestern University, DMR-0102794 Nanostructure formation is governed by a balance of bulk, surface and edge contributions to the energy. The former are associated with the relaxation of strain energy and are stabilizing while the latter are typically understood to represent an energy cost. Hybrid models combining continuum calculations of elastic strain fields with first-principles computations of surface energies were undertaken to study formation energetics of nanoscale faceted pyramid islands in Ge/Si(001) heteroepitaxy. The strain dependence of surface energy is found to be large and critically impacted by the presence of strain-induced changes in the Ge{100} surface reconstruction. The appreciable strain dependencies of {105} and {100} surface energies are calculated to give rise to a significant stabilization of islands with size scales on the order of 10 nm. Calculated trace of strain fields on a Ge nanoscale pyramid surface (top figure), showing relaxed (red) and compressively (blue) strained regions. Calculated contributions to island formation energies as a function of island size (lower figure); since the surface energy is negative the edge contributions are estimated and shown to be important for setting the island critical size.

2. NIRT: The Evolution and Self-Assembly of Quantum DotsP. W. Voorhees, A. Golovin, M. Asta, M. Miksis and S. Davis, Northwestern University, DMR-0102794 Education: Katsuyo Thornton and Mark Asta published a Topical Review article (see below) assessing the current status of computational-materials-science education in the US. The article was based on responses solicited from faculty in the top 20 materials departments in the country, as well as participants from industry and national labs. According to the publisher the article has been downloaded over 500 times during the past six months. This statistic likely reflects the intense interest in departments around the US in approaches for updating curricula related the teaching and use of computational tools in materials-science education. Outreach: Asta was co-organizer of the 2005-Fall MRS symposium “Modeling Morphological Evolution at Surfaces and Interfaces,” at which an international group of researchers from physics, materials and applied-math fields presented recent developments in state-of-the-art methods for modeling nano and mesoscale structure formation governed by surface and interface mediated growth processes.