Tim successfully defended his dissertation on February 5, 2009.

TITLE:
A Study of the Effects of Electromigration on Structures at the Nanoscale

ABSTRACT:
This thesis summarizes a study of the effects of electromigration, or diffusion influenced by applied electric fields, on nanoscale metallic structures. We have studied the impact of electromigration on two types of nanoscale systems, and as such the thesis naturally divides into two portions.

In the first portion, consisting of Chapters 2-4, we investigate the effects of electromigration on fluctuating step edges. When there is no electromigration present, a step undergoing motion by diffusion of atoms along its edge demonstrates power-law scaling in temporal correlation functions. This is verified by approximating the step as a continuum and using Langevin analysis; this approach is then extended to include electromigration forces. Under electromigration conditions, specifically for electromigration forces directed into or away from the step, we find theoretical deviations from the power-law scaling in the correlation function. We demonstrate this in two ways: through Monte Carlo simulation of step edges under electromigration conditions and through analysis of experimental measurements of current-stressed steps at the surface of silver films. We found good qualitative agreement with the theoretical expectations in both simulation and experiment, as well as good quantitative agreement in the results of the simulations.

The second portion of the thesis, consisting of Chapters 5 and 6, details an investigation of the effects of electromigration on the Rayleigh-Plateau instability in solid nanowires. We begin by deriving an equation of motion for a continuous cylinder and including an electromigration force along the symmetry axis of the cylinder. This is equivalent to a model of a nanowire carrying current, where the electromigration force is modeled as a constant.

We find power-law scaling in the pinching process with and without electromigration, though the effects of electromigration are to extend the life of the nanowire relative to those without electromigration. This is confirmed by conducting kinetic Monte Carlo simulations of aluminum nanowires under electromigration conditions. We find good agreement with the continuum model for the exponent in the power-law scaling as well as the effect of electromigration on the time at which pinching occurs. We also find evidence of self-similar behavior in the continuum model as well as in the simulations.

The nano-optics of surface plasmon polaritons and their applications in cloaking and microscopy Dr. Chris Davis, Professor of Electrical and Computer Engineering
University of Maryland College Park

In this talk I will describe what surface plasmon polaritons (SPPs) are, how they are excited, and how they can be used to produce both very large, and effectively negative, relative permittivities and group refractive indices. The effectively negative permittivities and refractive indices that can be produced in metal/dielectric composite nanostructures has allowed the first demonstration of 2-D cloaking in the visible part of the spectrum. The general principle and limitations of practical cloaking will also be discussed, and some of the approaches that are being considered for reducing the visibility of 3-D objects. The effectively large refractive indices that can be experienced by SPPs also allows the construction of super-resolution microscopes.

Location Physics Bldg., Room 401

Physics in Games Dr. Marc Olano
UMBC/CSEE

Modern computer games exhibit a number of elements of elementary physics. This is perhaps most visible in kinematic simulation of articulated bodies, the so-called "rag doll physics" for character animation. However, physics can also be found in fluid simulation, optical effects with participating media, and models of surface reflectance. These methods must run effectively on a range of consumer hardware, and must be fast, finishing within a fraction of the 10-30 ms time available per frame. This talk will present some of the currently popular methods and demonstrate their results, and discuss the state of consumer-level hardware to accelerate physics simulation.

Location Physics Bldg., room 401

Peering into Galaxies with Gamma-Ray Glasses Dr. Craig Markwardt
U. Maryland and NASA/Goddard Space Flight Center Most galaxies are thought to have a supermassive black hole at their center, as a natural consequence of the formation of structure in the universe. Finding these black holes is not as easy as it may seem however, because the centers of galaxies are often shrouded by obscuring material, which preferentially absorb optical and X-ray light. Most active galaxies found by surveys in the optical and X-ray wavelengths will thus be biased toward unobscured objects. However, as we move towards shorter wavelength X-rays - "hard X-rays" - the obscuring clouds become transparent. We have exploited this fact to construct a survey of all local active galaxies with the Swift Burst Alert Telescope, free of previous biases. While Swift and BAT were designed to chase and study gamma-ray bursts, the most powerful explosions in the universe, BAT is able to pierce the veil of obscuration surrounding local galaxies as well. I will present a summary of these results and compare to the properties of the supermassive black hole at the center of our own galaxy.

Location: Physics Bldg., room 401