Physics Commons^™

The Effects Of Strain And Vacancies On The Electric And Vibrational Properties Of Ferroelectric Batio3 From First-Principles, Aldo Serge Michael Raeliarijaona

Graduate Theses and Dissertations

The studies of ferroelectricity (FE) are of technological significance because of the multitude of applicable properties that ferroelectric materials exhibit. The mastery, and control of these properties necessitate the knowledge of the fundamental physics governing these insulating materials.

In this dissertation I present the results of first-principles investigations of the behavior of the fundamental ferroelectric properties under strain, and in the presence of vacancies. In the first part I introduce the important FE properties, their common behavior, and their numerous valuable applications. Following this background on FEs, a review of theoretical methods is presented with topics such as: Density Functional …

Photoelectric Characterization Of Bacteriorhodopsin Reconstituted In Lipid Bilayer Membrane, Joel Kamwa

Graduate Theses and Dissertations

The objective of this work was to conduct basic research in biologically inspired energy conversion solutions. A photosynthetic protein (Bacteriorhodopsin) was reconstituted in a bi-layer membrane. Then, when a laser beam was shined on the membrane, the photon energy was used by the protein to pump protons across the membrane. The translocation of protons across the membrane was measured as photocurrent. For this purpose, a system was built to characterize the lipid bilayer membranes and to measure the photocurrent. The lipid bilayer membrane was characterized by its capacitance and resistance. A picoampere photocurrent was observed when Bacteriorhodopsin protein was present …

The Role Of Quantum Dot Size On The Performance Of Intermediate Band Solar Cells, Najla Alnami

Graduate Theses and Dissertations

The goal of this thesis is to understand possible mechanisms for the reported decrease of the open circuit voltage and solar cell efficiency in quantum dot (QD) intermediate band solar cells (IBSCs). More specifically, the effect of indium arsenide (InAs) QD height on the open circuit voltage and solar cell efficiency was studied in a systematic way. To explore this effect in QD solar cells, several solar cells (SCs) were grown with varying InAs QD heights. All experimental characteristics of the QD solar cells were compared to a reference structure without QDs. All samples were grown by Molecular Beam Epitaxy …

Optimization Of Plasmon Decay Through Scattering And Hot Electron Transfer, Drew Dejarnette

Graduate Theses and Dissertations

Light incident on metal nanoparticles induce localized surface oscillations of conductive electrons, called plasmons, which is a means to control and manipulate light. Excited plasmons decay as either thermal energy as absorbed phonons or electromagnetic energy as scattered photons. An additional decay pathway for plasmons can exist for gold nanoparticles situated on graphene. Excited plasmons can decay directly to the graphene as through hot electron transfer. This dissertation begins by computational analysis of plasmon resonance energy and bandwidth as a function of particle size, shape, and dielectric environment in addition to diffractive coupled in lattices creating a Fano resonance. With …

Properties Of Multiferroic Bifeo3 From First Principles, Dovran Rahmedov

Graduate Theses and Dissertations

In this dissertation, a first-principle-based approach is developed to study magnetoelectric effect in multiferoic materials. Such approach has a significant predictive power and might serve as a guide to new experimental works. As we will discuss in the course of this work, it also gives an important insight to the underlying physics behind the experimentally observed phenomena.

We start by applying our method to investigate properties of a generic multiferroic material. We observe how magnetic susceptibility of such materials evolves with temperature and compare this evolution with the characteristic behavior of magnetic susceptibility for pure magnetic systems. Then we focus …

Multiscale Study Of Batio3 Nanostructures And Nanocomposites, Lydie Louis Louis

Graduate Theses and Dissertations

Advancements in integrated nanoelectronics will continue to require the use of unique materials or systems of materials with diverse functionalities in increasingly confined spaces.

Hence, research on finite-dimensional systems strive to unearth and expand the knowledge of fundamental physical properties in certain key materials which exhibit numerous concurrent and exploitable functions.

Correspondingly, ferroelectric nanostructures, which particularly display a plethora of complex phenomena, prevalent in countless fields of research, are noteworthy candidates. Presently, however, the assimilation of zero-(0D) and one-dimensional (1D) ferroelectric into micro- or nano-electronics has been lagging, in part due to a lack of applied and fundamental studies but …

The Geometry And Sensitivity Of Ion-Beam Sculpted Nanopores For Single Molecule Dna Analysis, Ryan Connor Rollings

Graduate Theses and Dissertations

In this dissertation, the relationship between the geometry of ion-beam sculpted solid-state nanopores and their ability to analyze single DNA molecules using resistive pulse sensing is investigated. To accomplish this, the three dimensional shape of the nanopore is determined using energy filtered and tomographic transmission electron microscopy. It is shown that this information enables the prediction of the ionic current passing through a voltage biased nanopore and improves the prediction of the magnitude of current drop signals when the nanopore interacts with single DNA molecules. The dimensional stability of nanopores in solution is monitored using this information and is improved …

Plasmonic Nanostructures For The Absorption Enhancement Of Silicon Solar Cells, Nathan Matthias Burford

Graduate Theses and Dissertations

In this work, computational investigation of plasmonic nanostructures was conducted using the commercial finite element electromagnetics solver Ansys® HFSS. Arrays of silver toroid nanoparticles located on the surface of an amorphous silicon thin-film absorbing layer were studied for particle sizes ranging from 20 nm to 200 nm in outer diameter. Parametric optimization by calculating an approximation of the photocurrent enhancement due to the nanoparticles was performed to determine optimal surface coverage of the nanoparticles. A comparison was made between these optimized nanotoroid arrays and optimized nanosphere arrays based on spectral absorption enhancement and potential photocurrent enhancement in an amorphous silicon …

Design And Fabrication Of Nanofluidic Systems With Integrated Sensing Electrodes For Rapid Biomolecule Characterization, Taylor Bradley Busch

Graduate Theses and Dissertations

A transparent nanofluidic system with embedded sensing electrodes was designed and fabricated by integrating Atomic Force Microscopy (AFM) nanolithography, Focused Ion Beam (FIB) milling and metal deposition, and standard microfabrication processing. The fabrication process started with the evaporation of chrome/gold (Cr/Au) onto a Pyrex 7740 wafer followed by photolithography and wet etching of the microchannels. The wafer was patterned a second time to form Au microelectrodes with 15-45 micrometer separation gaps in the nanochannel region. Sensing electrodes (up to one micron wide) were then deposited using FIB to bridge the gaps. The nanochannels were realized through both AFM nanolithography and …

Plasmonic And Photonic Designs For Light Trapping In Thin Film Solar Cells, Liming Ji

Graduate Theses and Dissertations

Thin film solar cells are promising to realize cheap solar energy. Compared to conventional wafer cells, they can reduce the use of semiconductor material by 90%. The efficiency of thin film solar cells, however, is limited due to insufficient light absorption. Sufficient light absorption at the bandgap of semiconductor requires a light path more than 10x the thickness of the semiconductor. Advanced designs for light trapping are necessary for solar cells to absorb sufficient light within a limited volume of semiconductor. The goal is to convert the incident light into a trapped mode in the semiconductor layer.

In this dissertation, …

Use Of Ultra High Vacuum Plasma Enhanced Chemical Vapor Deposition For Graphene Fabrication, Shannen Adcock

Graduate Theses and Dissertations

Graphene, what some are terming the "new silicon", has the possibility of revolutionizing technology through nanoscale design processes. Fabrication of graphene for device processing is limited largely by the temperatures used in conventional deposition. High temperatures are detrimental to device design where many different materials may be present. For this reason, graphene synthesis at low temperatures using plasma-enhanced chemical vapor deposition is the subject of much research. In this thesis, a tool for ultra-high vacuum plasma-enhanced chemical vapor deposition (UHV-PECVD) and accompanying subsystems, such as control systems and alarms, are designed and implemented to be used in future graphene growths. …

Using The Cern Program-Library Graphics And Interactive Data Display, Morgan T. Burks, Wilson H. Howe, Christine A. Byrd, Wilfred J. Braithwaite

Journal of the Arkansas Academy of Science

Small scale Monte Carlo programming is growing rapidly due to the ease with which complex problems may be formulated by any programmer. These programmers may choose to exploit graphics and interactive displays available in the program library developed and maintained by CERN (the Center for European Nuclear Research). This paper outlines the use of graphics and interactive data display features of the CERN program library, developed for visualizing simulated data events in particle detectors. One example uses GEANT, CERN's Monte Carlo modeling program, to simulate 300 MeV/c protons incident on a silicon slab. Display packages for GEANT are available both …

Principles And Clinical Applications Of Magnetic Resonance, Rao P. Gullapalli, Teresa T. Evans, Roger M. Hawk

Journal of the Arkansas Academy of Science

A review is presented which covers the basic theory of nuclear magnetic resonance (NMR) with regard to angular momentum, magnetic moments, and the classical mechanical description of the NMR experiment. Longitudinal (T,) and Transverse (T2) relaxation times are defined as well as the basic pulse sequences used for their measurement. In particular, the 180°-t-90° and the Hahn Spin Echo pulse sequences are described in detail. Basic Magnetic Resonance Imaging (MRI) theory is discussed with regard to slice selection, frequency encoding, and phase encoding to define the imaged volume element. The equations defining the amount of Tt , T2 , and …