Search Results

Quantum-Confined CdS Nanoparticles on DNA Templates

Description: As electronic devices became smaller, interest in quantum-confined semiconductor nanostructures increased. Self-assembled mesoscale semiconductor structures of II-VI nanocrystals are an especially exciting subject because of their controllable band gap and unique photophysical properties. Several preparative methods to synthesize and control the sizes of the individual nanocrystallites and the electronic and optical properties have been intensively studied. Fabrication of patterned nanostructures composed of quantum-confined nanoparticles is the next step toward practical applications. We have developed an innovative method to fabricate diverse nanostructures which relies on the size and a shape of a chosen deoxyribonucleic acid (DNA) template.
Date: May 1998
Creator: Rho, Young Gyu
Partner: UNT Libraries

Evaluation of dynamic and static electrical characteristics for the DY8 and YI8 process gallium diodes in comparison to the DI8 process boron diodes.

Description: A rectifier is an electrical device, comprising one or more semiconductor devices arranged for converting alternating current to direct current by blocking the negative or positive portion of the waveform. The purpose of this study would be to evaluate dynamic and static electrical characteristics of rectifier chips fabricated with (a) DY8 process and (b) YI8 process and compare them with the existing DI8 process rectifiers. These new rectifiers were tested to compare their performance to meet or exceed requirements of lower forward voltages, leakage currents, reverse recovery time, and greater sustainability at higher temperatures compared to diodes manufactured using boron as base (DI8 process diodes) for similar input variables.
Access: This item is restricted to the UNT Community Members at a UNT Libraries Location.
Date: December 2006
Creator: Dhoopati, Swathi
Partner: UNT Libraries

Magnetotransport Properties of AlxIn1-xAsySb1-y/GaSb and Optical Properties of GaAs1-xSbx

Description: Multilayer structures of AlxIn1-xAsySb1-y/GaSb (0.37 £ x £ 0.43, 0.50 £ y £ 0.52), grown by molecular beam epitaxy on GaSb (100) substrates were characterized using variable temperature Hall and Shubnikov-de Haas techniques. For nominally undoped structures both p and n-type conductivity was observed. The mobilities obtained were lower than those predicted by an interpolation method using the binary alloys; therefore, a detailed analysis of mobility versus temperature data was performed to extract the appropriate scattering mechanisms. For p-type samples, the dominant mechanism was ionized impurity scattering at low temperatures and polar optical phonon scattering at higher temperatures. For n-type samples, ionized impurity scattering was predominant at low temperatures, and electron-hole scattering dominated for both the intermediate and high temperature range. Analyses of the Shubnikov-de Haas data indicate the presence of 2-D carrier confinement consistent with energy subbands in GaAszSb1-z potential wells. Epilayers of GaAs1-xSbx (0.19<x<0.71), grown by MBE on semi-insulating GaAs with various substrate orientations, were studied by absorption measurements over the temperature range of 4-300 K. The various substrate orientations were chosen to induce different degrees of spontaneous atomic ordering. The temperature dependence of the energy gap (Eg) for each of these samples was modeled using three semi-empirical relationships. The resulting coefficients for each model describe not only the temperature dependence of Eg for each of the alloy compositions investigated, but also for all published results for this alloy system. The effect of ordering in these samples was manifested by a deviation of the value of Eg from the value of the random alloy. The presence of CuPt-B type atomic ordering was verified by transmission electron diffraction measurements, and the order parameter was estimated for all the samples investigated and found to be larger for the samples grown on the (111) A offcut orientations. This result strongly suggests ...
Date: May 2003
Creator: Lukic- Zrnic, Reiko
Partner: UNT Libraries

Ion-Induced Damage In Si: A Fundamental Study of Basic Mechanisms over a Wide Range of Implantation Conditions

Description: A new understanding of the damage formation mechanisms in Si is developed and investigated over an extended range of ion energy, dose, and irradiation temperature. A simple model for dealing with ion-induced damage is proposed, which is shown to be applicable over the range of implantation conditions. In particular the concept of defect "excesses" will be discussed. An excess exists in the lattice when there is a local surplus of one particular type of defect, such as an interstitial, over its complimentary defect (i.e., a vacancy). Mechanisms for producing such excesses by implantation will be discussed. The basis of this model specifies that accumulation of stable lattice damage during implantation depends upon the excess defects and not the total number of defects. The excess defect model is validated by fundamental damage studies involving ion implantation over a range of conditions. Confirmation of the model is provided by comparing damage profiles after implantation with computer simulation results. It will be shown that transport of ions in matter (TRIM) can be used effectively to model the ion-induced damage profile, i.e. excess defect distributions, by a simple subtraction process in which the spatially correlated defects are removed, thereby simulating recombination. Classic defect studies illuminate defect interactions from concomitant implantation of high- and medium-energy Si+-self ions. Also, the predictive quality of the excess defect model was tested by applying the model to develop several experiments to engineer excess defect concentrations to substantially change the nature and distribution of the defects. Not only are the excess defects shown to play a dominant role in defect-related processing issues, but their manipulation is demonstrated to be a powerful tool in tailoring the implantation process to achieve design goals. Pre-amorphization and dual implantation of different energetic ions are two primary investigative tools used in this work. Various analyses, ...
Date: May 2006
Creator: Roth, Elaine Grannan
Partner: UNT Libraries

Nonlinear Dynamics of Semiconductor Device Circuits and Characterization of Deep Energy Levels in HgCdTe by Using Magneto-Optical Spectroscopy

Description: The nonlinear dynamics of three physical systems has been investigated. Diode resonator systems are experimentally shown to display a period doubling route to chaos, quasiperiodic states, periodic locking states, and Hopf bifurcation to chaos. Particularly, the transition from quasiperiodic states to chaos in line-coupled systems agrees well with the Curry-Yorke model. The SPICE program has been modified to give realistic models for the diode resonator systems.
Date: May 1994
Creator: Yü, Chi
Partner: UNT Libraries

Workshop on Artificial Superlattices. October 30-31, 1980 at University of Illinois, Urbana-Champaign, Illinois, USA

Description: The program and 24 abstracts are given. The abstracts are divided into the following categories: structure and elastic properties, transport and electronic properties, magnetism and superconductivity, and phonons. The engineering of novel materials using sophisticated preparation techniques has received considerable attention in recent years. This interest has been mainly stimulated by recent developments in preparation techniques such as Molecular Beam Epitaxy, Thermal Vapor Deposition and Sputtering. These advances in deposition technology allow for the first time the preparation of layered materials with well defined layer thicknesses approaching interatomic spacing and opens up new avenues for the production and stabilization of materials that do not occur in nature. In addition to the extensive experimental work on artificial semiconductor superlattices there has been a parallel, almost independent, development relating to artificial metallic superlattices. Although the experimental sophistication of the field is considerable the development of major related theoretical ideas has not kept pace. In view of the large body of experimental work, a pressing need exists for the development of conceptual ideas relating to the novel physics that is created by artificially adding a new periodicity to the lattice. Because of this the Office of Naval Research is sponsoring the first "Workshop on Artificial Superlattices", October 30-31, 1980 at the University of Illinois, Urbana-Champaign. It is hoped that a small workshop, where theorists and experimentalists in metal and semiconductor physics are brought together, will be conducive to intimate interaction and development of new conceptual ideas.
Date: October 1980
Creator: Argonne National Laboratory
Item Type: Report
Partner: UNT Libraries Government Documents Department

Investigation of Manganese Dioxide as an Improved Solid Desiccant

Description: This report describes the preparation of a series of manganese oxides and an analysis of their sorptive, structural, and surface characteristics as low-energetic desiccants for passive dehumidification and active desiccant cooling systems. A cusped Type III isotherm for the adsorption of water is reported for the first time. The data are interpreted as evidence of a first-order phase change from a two-dimensional gas to a liquid film in the first reversibly adsorbed layer. It appears that the water adsorption characteristics of MnO2 compared to standard desiccants which exhibit Type II isotherms are due at least in part to differences in the physical topography and electronic properties of the desiccant substrates: MnO2 is a p-type semiconductor with essentially-flat, monoenergetic surface structures, while standard desiccants like silica gel are electronic insulators with irregular, heteroenergetic surfaces.
Date: March 1983
Creator: Fraioli, Anthony V.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Solution-based nanoengineering of materials.

Description: Solution-based synthesis is a powerful approach for creating nano-structured materials. Although there have been significant recent successes in its application to fabricating nanomaterials, the general principles that control solution synthesis are not well understood. The purpose of this LDRD project was to develop the scientific principles required to design and build unique nanostructures in crystalline oxides and II/VI semiconductors using solution-based molecular self-assembly techniques. The ability to synthesize these materials in a range of different nano-architectures (from controlled morphology nanocrystals to surface templated 3-D structures) has provided the foundation for new opportunities in such areas as interactive interfaces for optics, electronics, and sensors. The homogeneous precipitation of ZnO in aqueous solution was used primarily as the model system for the project. We developed a low temperature, aqueous solution synthesis route for preparation of large arrays of oriented ZnO nanostructures. Through control of heterogeneous nucleation and growth, methods to predicatively alter the ZnO microstructures by tailoring the surface chemistry of the crystals were established. Molecular mechanics simulations, involving single point energy calculations and full geometry optimizations, were developed to assist in selecting appropriate chemical systems and understanding physical adsorption and ultimately growth mechanisms in the design of oxide nanoarrays. The versatility of peptide chemistry in controlling the formation of cadmium sulfide nanoparticles and zinc oxide/cadmium sulfide heterostructures was also demonstrated.
Date: February 1, 2005
Creator: Criscenti, Louise Jacqueline; Spoerke, Erik David; Liu, Jun; Voigt, James A.; Cygan, Randall Timothy; Machesky, Michael L. (Illinois State Water Survey, Champaign, IL) et al.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Terahertz-based target typing.

Description: The purpose of this work was to create a THz component set and understanding to aid in the rapid analysis of transient events. This includes the development of fast, tunable, THz detectors, along with filter components for use with standard detectors and accompanying models to simulate detonation signatures. The signature effort was crucial in order to know the spectral range to target for detection. Our approach for frequency agile detection was to utilize plasmons in the channel of a specially designed field-effect transistor called the grating-gate detector. Grating-gate detectors exhibit narrow-linewidth, broad spectral tunability through application of a gate bias, and no angular dependence in their photoresponse. As such, if suitable sensitivity can be attained, they are viable candidates for Terahertz multi-spectral focal plane arrays.
Date: September 1, 2008
Creator: Lyo, Sungkwun Kenneth; Wanke, Michael Clement; Reno, John Louis; Shaner, Eric Arthur; Grine, Albert D. & Barrick, Todd A.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Microwave to millimeter-wave electrodynamic response and applications of semiconductor nanostructures: LDRD project 67025 final report.

Description: Solid-state lighting (SSL) technologies, based on semiconductor light emitting devices, have the potential to reduce worldwide electricity consumption by more than 10%, which could significantly reduce U.S. dependence on imported energy and improve energy security. The III-nitride (AlGaInN) materials system forms the foundation for white SSL and could cover a wide spectral range from the deep UV to the infrared. For this LDRD program, we have investigated the synthesis of single-crystalline III-nitride nanowires and heterostructure nanowires, which may possess unique optoelectronic properties. These novel structures could ultimately lead to the development of novel and highly efficient SSL nanodevice applications. GaN and III-nitride core-shell heterostructure nanowires were successfully synthesized by metal organic chemical vapor deposition (MOCVD) on two-inch wafer substrates. The effect of process conditions on nanowire growth was investigated, and characterization of the structural, optical, and electrical properties of the nanowires was also performed.
Date: November 1, 2006
Creator: Shaner, Eric Arthur; Lee, Mark; Averitt, R. D. (Los Alamos National Laboratory); Highstrete, Clark; Taylor, A. J. (Los Alamos National Laboratory); Padilla, W. J. (Los Alamos National Laboratory) et al.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Quantum coherence in semiconductor nanostructures for improved lasers and detectors.

Description: The potential for implementing quantum coherence in semiconductor self-assembled quantum dots has been investigated theoretically and experimentally. Theoretical modeling suggests that coherent dynamics should be possible in self-assembled quantum dots. Our experimental efforts have optimized InGaAs and InAs self-assembled quantum dots on GaAs for demonstrating coherent phenomena. Optical investigations have indicated the appropriate geometries for observing quantum coherence and the type of experiments for observing quantum coherence have been outlined. The optical investigation targeted electromagnetically induced transparency (EIT) in order to demonstrate an all optical delay line.
Date: February 1, 2006
Creator: Chow, Weng Wah Dr. (; .); Lyo, Sungkwun Kenneth; Cederberg, Jeffrey George; Modine, Normand Arthur & Biefeld, Robert Malcolm
Item Type: Report
Partner: UNT Libraries Government Documents Department

LDRD final report on engineered superconductivity in electron-hole bilayers.

Description: Macroscopic quantum states such as superconductors, Bose-Einstein condensates and superfluids are some of the most unusual states in nature. In this project, we proposed to design a semiconductor system with a 2D layer of electrons separated from a 2D layer of holes by a narrow (but high) barrier. Under certain conditions, the electrons would pair with the nearby holes and form excitons. At low temperature, these excitons could condense to a macroscopic quantum state either through a Bose-Einstein condensation (for weak exciton interactions) or a BCS transition to a superconductor (for strong exciton interactions). While the theoretical predictions have been around since the 1960's, experimental realization of electron-hole bilayer systems has been extremely difficult due to technical challenges. We identified four characteristics that if successfully incorporated into a device would give the best chances for excitonic condensation to be observed. These characteristics are closely spaced layers, low disorder, low density, and independent contacts to allow transport measurements. We demonstrated each of these characteristics separately, and then incorporated all of them into a single electron-hole bilayer device. The key to the sample design is using undoped GaAs/AlGaAs heterostructures processed in a field-effect transistor geometry. In such samples, the density of single 2D layers of electrons could be varied from an extremely low value of 2 x 10{sup 9} cm{sup -2} to high values of 3 x 10{sup 11} cm{sup -2}. The extreme low values of density that we achieved in single layer 2D electrons allowed us to make important contributions to the problem of the metal insulator transition in two dimensions, while at the same time provided a critical base for understanding low density 2D systems to be used in the electron-hole bilayer experiments. In this report, we describe the processing advances to fabricate single and double layer undoped samples, the ...
Date: January 1, 2005
Creator: Lyo, Sungkwun Kenneth; Dunn, Roberto G.; Lilly, Michael Patrick; Tibbetts-Russell, D. R.; Stephenson, Larry L.; Seamons, John Andrew et al.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Development of nanostructured and surface modified semiconductors for hybrid organic-inorganic solar cells.

Description: Solar energy conversion is increasingly being recognized as one of the principal ways to meet future energy needs without causing detrimental environmental impact. Hybrid organic-inorganic solar cells (SCs) are attracting particular interest due to the potential for low cost manufacturing and for use in new applications, such as consumer electronics, architectural integration and light-weight sensors. Key materials advantages of these next generation SCs over conventional semiconductor SCs are in design opportunities--since the different functions of the SCs are carried out by different materials, there are greater materials choices for producing optimized structures. In this project, we explore the hybrid organic-inorganic solar cell system that consists of oxide, primarily ZnO, nanostructures as the electron transporter and poly-(3-hexylthiophene) (P3HT) as the light-absorber and hole transporter. It builds on our capabilities in the solution synthesis of nanostructured semiconducting oxide arrays to this photovoltaic (PV) technology. The three challenges in this hybrid material system for solar applications are (1) achieving inorganic nanostructures with critical spacing that matches the exciton diffusion in the polymer, {approx} 10 nm, (2) infiltrating the polymer completely into the dense nanostructure arrays, and (3) optimizing the interfacial properties to facilitate efficient charge transfer. We have gained an understanding and control over growing oriented ZnO nanorods with sub-50 nm diameters and the required rod-to-rod spacing on various substrates. We have developed novel approaches to infiltrate commercially available P3HT in the narrow spacing between ZnO nanorods. Also, we have begun to explore ways to modify the interfacial properties. In addition, we have established device fabrication and testing capabilities at Sandia for prototype devices. Moreover, the control synthesis of ZnO nanorod arrays lead to the development of an efficient anti-reflection coating for multicrystalline Si solar cells. An important component of this project is the collaboration with Dr. Dave Ginley's group at NREL. The ...
Date: September 1, 2008
Creator: Hsu, Julia, W. P.
Item Type: Report
Partner: UNT Libraries Government Documents Department

Assembling semiconductor nanocomposites using DNA replication technologies.

Description: Deoxyribonucleic acid (DNA) molecules represent Nature's genetic database, encoding the information necessary for all cellular processes. From a materials engineering perspective, DNA represents a nanoscale scaffold with highly refined structure, stability across a wide range of environmental conditions, and the ability to interact with a range of biomolecules. The ability to mass-manufacture functionalized DNA strands with Angstrom-level resolution through DNA replication technology, however, has not been explored. The long-term goal of the work presented in this report is focused on exploiting DNA and in vitro DNA replication processes to mass-manufacture nanocomposite materials. The specific objectives of this project were to: (1) develop methods for replicating DNA strands that incorporate nucleotides with ''chemical handles'', and (2) demonstrate attachment of nanocrystal quantum dots (nQDs) to functionalized DNA strands. Polymerase chain reaction (PCR) and primer extension methodologies were used to successfully synthesize amine-, thiol-, and biotin-functionalized DNA molecules. Significant variability in the efficiency of modified nucleotide incorporation was observed, and attributed to the intrinsic properties of the modified nucleotides. Noncovalent attachment of streptavidin-coated nQDs to biotin-modified DNA synthesized using the primer extension method was observed by epifluorescence microscopy. Data regarding covalent attachment of nQDs to amine- and thiol-functionalized DNA was generally inconclusive; alternative characterization tools are necessary to fully evaluate these attachment methods. Full realization of this technology may facilitate new approaches to manufacturing materials at the nanoscale. In addition, composite nQD-DNA materials may serve as novel recognition elements in sensor devices, or be used as diagnostic tools for forensic analyses. This report summarizes the results obtained over the course of this 1-year project.
Date: November 1, 2005
Creator: Heimer, Brandon W.; Crown, Kevin K. & Bachand, George David
Item Type: Report
Partner: UNT Libraries Government Documents Department

Hydrogen terminated silicon surfaces: Development of sensors to detect metallic contaminants and stability studies under different environments

Description: Hydrogen terminated silicon surfaces have been utilized to develop sensors for semiconductor and environmental applications. The interaction of these surfaces with different environments has also been studied in detail. The sensor assembly relevant to the semiconductor industry utilizes a silicon-based sensor to detect trace levels of metallic contaminants in hydrofluoric acid. The sensor performance with respect to two non-contaminating reference electrode systems was evaluated. In the first case, conductive diamond was used as a reference electrode. In the second case, a dual silicon electrode system was used with one of the silicon-based electrodes protected with an anion permeable membrane behaving as the quasi reference electrode. Though both systems could function well as a suitable reference system, the dual silicon electrode design showed greater compatibility for the on-line detection of metallic impurities in HF etching baths. The silicon-based sensor assembly was able to detect parts- per-trillion to parts-per-billion levels of metal ion impurities in HF. The sensor assembly developed for the environmental application makes use of a novel method for the detection of Ni2+using attenuated total reflection (ATR) technique. The nickel infrared sensor was prepared on a silicon ATR crystal uniformly coated by a 1.5 micron Nafion film embedded with dimethylglyoxime (DMG) probe molecules. The detection of Ni2+ was based on the appearance of a unique infrared absorption peak at 1572 cm-1 that corresponds to the C=N stretching mode in the nickel dimethylglyoximate, Ni(DMG)2, complex. The suitable operational pH range for the nickel infrared sensor is between 6-8. The detection limit of the nickel infrared sensor is 1 ppm in the sample solution of pH=8. ATR - FTIR spectroscopy was used to study the changes that the hydride mode underwent when subjected to different environments. The presence of trace amounts of Cu2+ in HF solutions was found to roughen the silicon ...
Date: August 2002
Creator: Ponnuswamy, Thomas Anand
Partner: UNT Libraries

A Study of Atomic Ordering in III-V Semiconductors

Description: Thesis written by a student in the UNT Honors College discussing semiconductors and band structure, the temperature-induced variation of the band structure, the atomic structure of III-V materials, atomic ordering of the band structure, and experimental techniques regarding atomic ordering of CuPt-B.
Date: Summer 2002
Creator: Cottier, Ryan J.
Partner: UNT Honors College

Shubnikov-de Haas Effect Under Uniaxial Stress: A New Method for Determining Deformation Potentials and Band Structure Information in Semiconductors

Description: The problem with which this investigation is concerned is that of demonstrating the applicability of a particular theory and technique to two materials of different band structure, InSb and HgSe, and in doing so, determining the deformation potentials of these materials. The theory used in this investigation predicts an inversion-asymmetry splitting and an anisotropy of the Fermi surface under uniaxial stress. No previous studies have ever verified the existence of an anisotropy of the Fermi surface of semiconductors under stress. In this work evidence will be given which demonstrates this anisotropy. Although the inversion-asymmetry splitting parameter has been determined for some materials, no value has ever been reported for InSb. The methods presented in this paper allow a value of the splitting parameter to be determined for InSb.
Date: December 1972
Creator: Hathcox, Kyle Lee
Partner: UNT Libraries