Search

Ferromagnetic ring elements on the micrometer and submicrometer scale exhibit flux-closure magnetic vortex states in an intermediate step of their magnetization reversal. These clockwise or counterclockwise flux-closure states are of interest for applications that encode binary information in magnetic elements. Here, we study the magnetization reversal process of triangular cobalt rings made by e-beam lithography and lift-off. We demonstrate that full control over the direction of flux-closure magnetic states can be achieved solely by homogeneous external magnetic fields applied in particular directions. We have extracted statistical experimental data pertaining to the range of critical field values that trigger magnetization reversal from magnetic force microscopy images, and we explain the results on the basis of micromagnetic simulations. Index Terms--Magnetic devices, magnetic ring elements, magnetization reversal, micromagnetics.

Two-dimensional effective-mass Schrodinger equation for scattering states in a domain with an open boundary is solved by a numerical method. This technique is based on the partial wave expansion of the unknown asymptotic wave function and on the complex wave function continuity and its derivative across the domain boundary. The linear system of equations, obtained by standard numerical techniques, are solved to derive the total wave function within the numerical domain. The validity of this method is demonstrated by three different scattering geometries.

A two-dimensional numerical algorithm analyzes the boundary conditions for exposed semiconductor-surface-based potential in split-gate structures. The algorithm couples finite element principles for the semiconductor-based nonlinear Poisson equation and the boundary element principle for the dielectric Laplace equation. Oxide-based interactions that occur alter the trap emission dynamics.

Potential building blocks for quantum cellular automata architectures are constituted by the model quantum dot cells. Few electrons are found in each cell, and the cells interact Coulombically with nearly cells. There is an alignment in the cell caused by the acceptable cell designs. The cell-cell response function quantifiers are also studied. Programable logic gate structures are also developed as a part of the experimental investigation.

A numerical modeling of the lateral positive-negative-positive quantumwire system in a GaAs/AlGaAs heterostructure device is discussed. The wire is formed in the v-shaped groove of a semi-insulating SI-GaAs substrate. The wire's electrostatic potential and effective conduction band density are expressed in terms of two-dimensional Poisson and Schrodinger equations. These equations are then solved by means of the finite element method. The heterostructure device is found to have several possible advantages over sidewall etched electrostatically confined systems.

The Nano-Devices Group at the University of Notre Dame proposed a new device that encodes information in the geometrical charge distribution of artificial (or natural) molecules. Functional units are composed by electrostatic coupling. In these units, processing takes place by reshaping the electron density of the molecules, and not by switching currents [1]. Signal processing potential of next-neighbor-coupled cellular nonlinear networks (CNN's) has been recently explored with the conclusion that local-activity of the cells is necessary to exhibit complexity [2]. It will be shown that Coulomb-coupled time-invariant artificial molecules behave like nonlinear locally passive devices, thus signal-power-gain or multiple equilibria cannot be achieved by integrating them. However, the signal input--output relation of strongly nonlinear molecules can be varied in time by adiabatic pumping, called clock control. It will be shown that strongly nonlinear time-varying molecules can transform the necessary amount of clock energy into the signal flow, thereby enabling the network of molecules to perform signal processing.

Nano is a prefix derived from the Greek word for dwarf, and it means one-billionth of something. So a nanosecond is a billionth of a second, and a nanometer is [...]