Session K4: DMP/CSWP Prize Symposium

Nanocrystals, Nanowires and the Role of Quantum Confinement

One of the most challenging issues in materials physics is to predict the properties of matter at the nanoscale. In this size regime, new structural and electronic properties exist that resemble neither the atomic, nor solid state. By changing the size of the system, inherently intensive properties become extensive properties, which can be strongly altered from the macroscopic limit. Such properties can have profound technological implications, e.g., at small length scales a poor optical material like silicon can be converted to an optically active one. Unfortunately, the development of theoretical methods to predict the properties of these systems is formidable challenge. Nanoscale systems may contain thousands of electrons and atoms, and often possess little symmetry. I will illustrate some recent advances in this area based on methods that are designed to exploit high performance computational platforms. I will present real space pseudopotential techniques for solving the electronic structure problem within density functional theory (see http://www.ices.utexas.edu/parsec). I will apply these techniques to systems ranging from clusters of a few dozen atoms to systems containing over a thousand atoms. I will present predictions for the structural and electronic properties of semiconductor nanowires and nanocrystals, intrinsic and doped, and will resolve some outstanding issues in the literature.   

Near-field intensity correlations in metal-dielectric nano-composites

Spatial correlations of field and intensity are indicative of the nature of wave transport in random media and have been widely investigated in the context of electromagnetic wave propagation in disordered dielectric systems However, less is known of near-field intensity correlations in metallic random systems, which can exhibit rich phenomena due the involvement of intrinsic resonance effects-surface plasmons. Neither is clear the difference between correlation functions in metallic and dielectric systems. This paper presents the first experimental study of near-field intensity correlations in metal-dielectric systems in regimes where localization and delocalization are expected. Significant differences are observed between the spatial intensity correlations functions in metal-dielectric systems and those of purely dielectric random media. In disordered metallic nanostructures, surface plasmon modes are governed by the structural properties of the system and may be strongly localized. Recent theoretical studies of metallic nanoparticle aggregates suggest that the eigenmodes of such systems may have properties of both localized and delocalized states. However, it is not clear how such eigenmodes impact the propagation or localization of surface plasmon polaritons excited by impinging light, an issue addressed in this study. In the current experiment, the concentration of metal particles on a dielectric surface $p$ was varied over a wide range to control the amount of scattering. Spatial intensity correlations obtained from near-field optical microscopy (NSOM) images show a transition from propagation to localization and back to propagation of optical excitations in planar random metal-dielectric systems with increase in metal filling fraction.   

Carbon Nanotubes: Recent Results and Directions

This talk will present our latest research on single walled carbon nanotubes. We have been using carbon nanotube as a model system to study interesting nanoscale problems concerning materials synthesis, solid-state physics and devices, surface science and nanobiotechnology. This presentation will cover our latest results in, (1) Controlled synthesis of nanotube structures on surfaces. (2) Coherent quantum electron transport and diffusive electron-phonon scattering phenomena in suspended nanotubes. (3) Pushing the performance limit of nanotube transistors, and (4) interfacing carbon nanotubes with biological systems including living cells.   

Exploiting the unique electronic and mechanical properties of carbon and boron nitride nanotubes

Carbon and boron nitride nanotubes have unusual geometrical features that affect their electronic, thermal, and mechanical properties. I will discuss relevant experimental studies of the underlying physics, as well as possible applications including sensors, nanoscale electric motors, high frequency tunable resonators, and phonon waveguides.