Control of New Kinetic Barriers & Design of Nanorods

The accomplishments of this project include three elements. The first element directly relates to the focus of this project. Specifically, we have determined the three-dimensional Ehrlich-Schwoebel barriers, with and without surfactants, and two manuscripts in preparation; references refer to the list of journal publications. Further, we have discovered a characteristic length scale - the dimension of atomic islands bounded by multiple-layer surface steps. This discovery has made it possible to understand scientifically why nanorods synthesis is possible at all, will enable science-based design of nanorods, and may impact energy technology through nanomaterials design and synthesis. The second element relates to an exploration - synthesis of nanowires. This exploration is made possible through additional support of a Small Grant Exploratory Research from NSF. Through a combination of atomistic simulations, theories, and experiments, the PI and colleagues have made two contributions to the field. Specifically, they have revealed the physical reason why periodic twins develop during growth of SiC nanowires. Further, they have discovered that SiC nanowire films have an order-of-magnitude higher friction that their macroscopic counterpart, something that has never been reported before. The third elements relates to knowledge dissemination. The PI has co-edited (with Helena van Swygenhoven of PSI) an issue of MRS Bulletin, with the theme of Atomistic Simulations of Mechanics of Nanostructures, co-authored a review article in JOM, and authored a review paper in connection with a Banff workshop series co-sponsored by Canada, US, and Mexico

Clustering on Magnesium Surfaces – Formation and Diffusion Energies

The formation and diffusion energies of atomic clusters on Mg surfaces determine the surface roughness and formation of faulted structure, which in turn affect the mechanical deformation of Mg. This paper reports first principles density function theory (DFT) based quantum mechanics calculation results of atomic clustering on the low energy surfaces {0001} and {1011}. In parallel, molecular statics calculations serve to test the validity of two interatomic potentials and to extend the scope of the DFT studies. On a {0001} surface, a compact cluster consisting of few than three atoms energetically prefers a facecentered- cubic stacking, to serve as a nucleus of stacking fault. On a {1011}, clusters of any size always prefer hexagonal-close-packed stacking. Adatom diffusion on surface {1011} is high anisotropic while isotropic on surface (0001). Three-dimensional Ehrlich–Schwoebel barriers converge as the step height is three atomic layers or thicker. Adatom diffusion along steps is via hopping mechanism, and that down steps is via exchange mechanism