Left: View of the ErSi 2 nanowire along the [110] direction

1. First-Principles Theory of Er Silicide Nanowire Formation on Si(001)PI: Vidvuds Ozolins, UCLA, DMR-0427638 Atoms of Erbium, when deposited on the high-symmetry (001) surface of Si, form very long (many microns) wires of ErSi2 that are only a few nanometers wide and one atomic layer thick. Excellent electronic properties of ErSi2, such as low Schottky barrier, make these systems interesting for applications in ultra-high-density microelectronics. We have investigated the physics of nanowire formation using Left: View of the ErSi2 nanowire along the [110] direction (perpendicular to wire). Right: The calculated valence charge density of the ErSi2 nanowire. large-scale first-principles electronic structure calculations. We find that surface reconstruction stabilizes these nanowires energetically and induces important changes in the electronic structure and physical properties. Traditional considerations based on the properties of bulk ErSi2 are shown to be highly misleading when applied to nanowires. Calculated surface stresses, boundary energies and anisotropic Er surface diffusion coefficients are used to provide a theoretical explanation for the spontaneous formation of nanowires. This research has been carried out by graduate students at UCLA.

2. Predicting Structures from First-Principles Electron-Structure Calculations: Smoothing of Energy LandscapesPI: Vidvuds Ozolins, UCLA, DMR-0427638 A persistent difficulty in designing new materials theoretically using modern electron-structure techniques is the need to predict detailed structural information at the atomic level. The search for stable structures is complicated by the existence of multiple local minima in the configuration space, the number of which increases exponentially with the number of atoms. We have developed a novel approach of structural optimization in multicomponent systems which is based on smoothing of the total energy landscape and eliminating most of the high-energy local minima. This method is being used to study the structure of bulk alloys, metallic nanoparticles and surface systems without any approximations beyond standard density functional theory (DFT). Graduate students from underrepresented groups are involved in carrying out this research. Evolution of the total structural energy during optimization for the ternary Al-Mg-Si system. The inset shows the predicted lowest-energy structure of a ternary AlMg5Si5 precipitate.