Engineering Commons^™

Stability And Optimization Of Photoconductivity In Thermally Vacuum Evaporated Indium (Iii) Sulfide Thin Films, Gustavo Rehder, Robert Engelken, Randy Stidham, Richard Tanner, Lee Ketchum, Anil Baral

Journal of the Arkansas Academy of Science

Long term stability of photosensitivity versus time in indium (III) sulfide thin films thermally vacuum evaporated onto photocell-patterned printed circuit boards varies sensitively with several factors including contact metal type, contact metal diffusion and electromigration into the semiconductor, doping, and encapsulation method. Because of the significant photoconductivity and relative low toxicity and environmental impact of this compound semiconductor, it is important to better characterize these dependences toward commercial applications. We will report on measurements of photoconductivity vs. time as functions of such factors and evolving methods to stabilize this photoconductivity.

The Effect Of Weak Acids Hydrolysis On The Sol-Gel Fabrication Of Silica Thin Film, Abdul Hamid

Student Works (2000-2009)

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Neodymium And Erbium Coordination Environments In Phosphate Glasses, Mevlüt Karabulut, G. K. Marasinghe, Ezzeldin Metwalli, Andrew K. Wittenauer, Richard K. Brow, C. H. Booth, D. K. Shuh

Materials Science and Engineering Faculty Research & Creative Works

The local structures of Nd3+ and Er3+ ions in two series of rare-earth (RE) phosphate glasses with nominal compositions xR203-(1-x)P2O5, where R=Nd and Er and 0.05≤x≤0.28, have been characterized by LIII-edge extended x-ray-absorption fine-structure spectroscopy (EXAFS). The RE coordination number depends on the R2O3 content, decreasing from 9.0 (10) oxygen nearest neighbors in ultraphosphate compositions (x<0.15) to 6.4 (9) oxygen nearest neighbors for the metaphosphate (x∼0.25) compositions. The average Er-O bond distance decreases from 2.29 (1) to 2.23 (1) Å, and the average Nd-O bond distance decreases from 2.40 (1) to 2.37 (1) Å over the same compositional range. The changes in coordination environments are consistent with the conversion of isolated RE polyhedra to clustered RE polyhedra sharing common oxygens as the number of available terminal oxygens per RE ion decreases with increasing x.

Thermogravimetric Studies Of Pmma On Silica, Bing Zhang, Frank D. Blum

Chemistry Faculty Research & Creative Works

The thermal degradation of poly(methyl methacrylate) (PMMA) has been studied extensively. It is well accepted that the degradation process is a radical chain reaction involving initiation, depropagation, transfer, and termination reactions. In the degradation process, the factors having observable effects on the decomposition behavior include molecular mass, polydispersity, tacticity, and sample dimensions. The effects of tacticity on the degradation behavior of PMMA were investigated by Kashiwagi et al., Jellinek et al. And Chiamtore et al. The results indicated that both isotactic and syndiotactic PMMA have similar decomposition pathways and activation energies. Isotactic PMMA will decompose at a slightly lower temperature …

Effect Of Polymer-Surface Mobility On Adhesion In Poly(Methyl Methacrylate)-Tape System, Bhavesh C. Gandhi, Frank D. Blum, Lokeswarappa R. Dharani

Chemistry Faculty Research & Creative Works

The interaction between two polymer layers, especially adhesion between them, plays an important role in polymer processing and other applications. Detailed knowledge of the molecular structure and dynamics of polymer interfaces, and how they relate to macroscopic mechanical properties, should help designers construct more functional systems. Unfortunately, there have been few studies where both molecular and macroscopic studies have been performed on similar systems. In previous studies from our group, we have probed the dynamics of poly(methyl acrylate) (PMA) and thermal behavior of poly(methyl methacrylate) (PMMA) on silica. These studies helped us paint a picture for strongly bound molecules on …

Defect And Mixed Conductivity In Nanocrystalline Doped Cerium Oxide, Toshio Suzuki, Igor Kosacki, Harlan U. Anderson

Materials Science and Engineering Faculty Research & Creative Works

The results obtained from a study on the microstructure and the electrical properties of Gd-doped CeO₂ thin films were reported. Dense, nanocrystalline films on sapphire substrates are prepared using a polymeric precursor spin coating technique. The electrical conductivity was studied as a function of temperature and oxygen activity and correlated with the grain size. For nanocrystalline Gd-doped CeO₂ thin films, the ionic conductivity increased with decreasing activation energy as the grain size decreased. A conductivity model was developed to analyze PO₂ behavior of the electrical conductivity. Using the conductivity model, the hopping energy of electron conduction and …

Heat Transfer In A Thin Liquid Film In The Presence Of Electric Field For Non-Isothermal Interfacial Condition, Rama S.R. Gorla, Jorge E. Gatica, Bahman Ghorashi, Pijarn In-Eure, Larry W. Byrd

Chemical & Biomedical Engineering Faculty Publications

Heat transfer enhancement in an evaporating thin liquid film using the electric field under non-isothermal interfacial condition is presented. A new mathematical model subjected to van der Waals attractive forces, the capillary pressure and the electric field is developed to describe the heat transfer enhancement in the evaporating thin liquid film. The effect of an electrostatic field on the curvature of the thin film, evaporative flux, pressure gradient distribution, heat flux, and heat transfer coefficient in the thin film is presented. The results show that the electric field can enhance heat transfer in the thin liquid film significantly. In addition, …

Effect Of Oxygen Vacancies On The Magnetic Structure Of The La₀.₆Sr₀.₄Feo3-Δ Perovskite: A Neutron Diffraction Study, Zili Chu, William B. Yelon, Jinbo Yang, William Joseph James, Harlan U. Anderson, Yixiang Xie, Satish K. Malik

Physics Faculty Research & Creative Works

Magnetic interactions in perovskite compounds of the type La_1-xSr_xMO_3-δ (M=3d transition such as Mn and Fe) are presumed to arise through a super exchange between 3d electrons of the magnetic ions via oxygen orbitals. The magnetic structure of La_0.6Sr_0.4FeO_3-δ has been studied with neutron diffraction. Oxygen vacancies were created by annealing samples under various gases including N₂, air and mixtures of CO/CO₂. All La_0.6Sr_0.4FeO_3-δ compounds maintain the rhombohedral structure (space group R3̄c). The air- or oxygen-annealed samples have almost no oxygen …

Thermoelectric Properties Of Bi2sr2co2o9 Whiskers Under Hydrostatic Pressure, F Chen, Kevin L. Stokes, Ryozi Funahashi

Physics Faculty Publications

We report the temperature dependence of thermopower (S) in the ab plane of Bi2Sr2Co2O9 {BC-222} single crystalline whiskers under high pressure up to 1.2 GPa. Special modifications were made to our high-pressure transport measurement system to improve the measurement accuracy of S for whiskers with high resistance. Pressure improved the contact resistance dramatically. We observed a slight decrease of  S and four-wire electrical conductivity (sigma) under high pressure. As a result, the power factor (S2sigma) was decreased less than 20% by pressure. From the temperature dependence of sigma, the band gap of BC-222 whiskers increase very slightly …

Oxidation-Induced Stacking Fault In (100) And (111) Silicon Wafers, Mei Keat Liang

Student Works (2000-2009)

Oxidation-induced stacking fault (OISF) dimension and density change on (100) and (111) wafers, as a result of repeated preferential etching were studied using AFM. optical microscope and angular polishing techniques. Density on (100) and (111) wafers is independent of surface removal up to 3.0µm. This indicates the single layer nature of OISF formed from the sand blasted wafer. Besides having higher density, OISFs from (100) wafer were longer than OISF from (111) wafer. OISF width increases linearly with surface removal however the length does not change significantly with surface removal. ln the OISF normal depth studies using angular polishing technique, …

High-Efficiency Solar Cells Based On Cu(Inal)Se[Sub 2] Thin Films, S. Marsillac, P. D. Paulson, M. W. Haimbodi, R. W. Birkmire, W. N. Shafarman

Electrical & Computer Engineering Faculty Publications

A Cu(InAl)Se₂solar cell with 16.9% efficiency is demonstrated using a Cu(InAl)Se₂thin film deposited by four-source elemental evaporation and a device structure of glass/Mo/Cu(InAl)Se₂/CdS/ZnO/indium tin oxide/(Ni/Algrid)/MgF₂. A key to high efficiency is improved adhesion between the Cu(InAl)Se₂ and the Mo back contact layer, provided by a 5-nm-thick Ga interlayer, which enabled the Cu(InAl)Se₂ to be deposited at a 530 °C substrate temperature. Film and device properties are compared to Cu(InGa)Se₂ with the same band gap of 1.16 eV. The solar cells have similar behavior, with performance limited by recombination through …

Iron Phosphate Glass For The Vitrification Of Ineel Sodium Bearing Waste And Hanford Low Activity Waste, Robert Douglas Leerssen

Masters Theses

"The current study investigates the feasibility of using iron phosphate glass for the immobilization of nuclear wastes that have limited solubility in the current borosilicate glass used for vitrification. These wastes contain elements such as sulfur and phosphorus, which have proven problematic (causing phase separation at >1 wt%) for vitrification in borosilicate glasses, as well as having a high soda content (50-75 wt%) which also limits wasteloading"--Abstract, page iv.

Growth Dependant Properties Of Undoped And In-Situ Doped Chemically Deposited Cds Thin Films, Aaron John Reynolds

Theses : Honours

This research project examines the growth dependant properties and composition of Cadmium Sulfide thin films produced by the Chemical Bath Deposition Method. The specific areas investigated are the effect of deposition temperature, the effect of an Indium dopant on the films structure and properties, and the effects of post deposition processing such as annealing in air on the film composition. The chemical bath deposition apparatus used has been refined and tested to ensure that the films were grown in a more efficient manner than previously, with more control of the influencing deposition parameters such as temperature. Films grown by the …

Raman Spectroscopy Of Nanocrystalline Ceria And Zirconia Thin Films, Igor Kosacki, Vladimir Petrovsky, Harlan U. Anderson, Philippe Colomban

Materials Science and Engineering Faculty Research & Creative Works

The results of Raman-scattering studies of nanocrystalline CeO₂ and ZrO₂:16% Y (YSZ) thin films are presented. The relationship between the lattice disorder and the form of the Raman spectra is discussed and correlated with the microstructure. It is shown that the Raman line shape results from phonon confinement and spatial correlation effects and yields information about the material nonstoichiometric level.

Misinformation [1], Hollis P. Leighly

Materials Science and Engineering Faculty Research & Creative Works

No abstract provided.

Evaluating And Monitoring Nucleation And Growth In Copper Foil, Ye Kun Lee, Thomas J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

The electrodeposition of copper foil for use in electronic materials applications is a complex and demanding process. The specific aspects of producing and controlling the structure-property-performance requirements of the foil are important because of the stringent demands placed on their use in printed circuit boards and similar products. In this paper, a brief review of the electrodeposition process for raw copper foil is presented. Since electrolyte additives play such a significant role in the copper-deposition process, the effects of two essential additives, chloride ion and an organic (e.g., glue or gelatine), on the foil are described. Also, the influence of …

Reactive Hot Pressing Of Alumina-Molybdenum Disilicide Composites, William Fahrenholtz, Ronald E. Loehman, Kevin G. Ewsuk

Materials Science and Engineering Faculty Research & Creative Works

Al₂O₃-MoSi₂ Composites Were Prepared by Reactive Hot Pressing using Molybdenum, Aluminum, and Mullite Powders as Precursors. the Gibbs Free Energy Was Highly Negative for the Composite-Forming Reaction, Which Indicated that the Products Were Stable Relative to the Reactants. after the Reaction, the Composites Had High Relative Density, ∼96%. based on the Composite-Forming Reaction, the Composites Should Have Contained 18 Vol% MoSi₂ in an Al₂O₃ Matrix. Scanning Electron Microscopy Revealed that the MoSi2 Inclusions Were Elongated, with an Average Thickness of ∼5 Μm and Inclusion Lengths that Ranged from 5 to 50 …

Agglomerated Lubricant, Mary R. Reidmeyer

Materials Science and Engineering Faculty Research & Creative Works

A lubricant for use in lubricating the shot sleeve of a machine for die casting molten metals is in the form of agglomerated particles. The particles have an inorganic high pressure lubricant agglomerated, with a binder material and with an organic material. The solid lubricant is resistant to dusting, caking and breakage, can be fed through an automatic dispensing machine, and combines inorganic and organic materials to achieve excellent lubrication properties. The product has low flash and low smoke release into the environment.

Modeling, Fabrication, And Optimization Of Niobium Cavities: Phase Ii Second Quarterly Report, Robert A. Schill Jr., Mohamed Trabia

Transmutation Sciences Materials (TRP)

Niobium cavities are important parts of the integrated NC/SC high-power linacs. Over the years, researchers in several countries have tested various cavity shapes. They concluded that elliptically shaped cells are the most appropriate shape for superconducting cavities. The need for very clean surfaces lead to the use of a buffered chemical polishing produce for surface cleaning to get good performance of the cavities. Up to this point, the second phase has resulted in the design of an experimental setup for the fluid flow experiment. Other experimental activities include the evaluation of a vacuum system are underway. Little reportable progress has …

Modeling, Fabrication, And Optimization Of Niobium Cavities, Robert A. Schill Jr., Mohamed Trabia, Yitung Chen

Transmutation Sciences Materials (TRP)

All technologies for the transmutation of nuclear waste require a large source of neutrons. One of the principal methods of generating these neutrons is by using a particle accelerator to bombard a heavy metal target. One of the more promising designs for particle accelerators for transmutation systems is the Superconducting Radio Frequency (RF) high-current linear accelerator (linac). The power supplies for these systems have three major components: niobium cavities, power couplers, and cryomodules. This research project will develop models to predict the behavior and performance of the niobium cavities, which will then be used to design and optimize the superconducting …

Experimental Investigation Of Steel Corrosion In Lead Bismuth Eutectic (Lbe): Characterization, Species Identification, And Chemical Reactions, John Farley, Dale L. Perry, Allen L. Johnson

Transmutation Sciences Materials (TRP)

The goal of the present research is to achieve a basic understanding of corrosion of steels by Lead Bismuth Eutectic (LBE). Liquid LBE is under consideration in the transmuter as both a spallation target and as a blanket coolant. There have been previous studies of LBE, especially by the Russians, who have over 80 reactor-years experience with LBE coolant in their Alpha-class submarine reactors. However, a fundamental understanding and verification of its role in the corrosion of steels is still very incomplete. We have begun a program of post-experiment testing and analysis on steel samples that have been in intimate …

Corrosion Of Steel By Lead Bismuth Eutectic, John Farley, Dale L. Perry, Allen L. Johnson

Transmutation Sciences Materials (TRP)

This research program will analyze various steel samples that have been exposed to LBE as part of the national program to develop LBE and transmutation technologies. This information will be paramount in developing engineering efforts to control, avoid, and/or minimize the effect of corrosion of steels by LBE in transmuter and LBE systems. Additionally, this program provides UNLV researchers with hands-on experience that will be crucial in developing the UNLV LBE program, supporting the University’s mission with the ISTC target complex, and the future development of additional facilities to examine LBE systems.

The research group plans to test the hypothesis …

Corrosion Of Steel By Lead Bismuth Eutectic: Year 1 Annual Report, John Farley

Transmutation Sciences Materials (TRP)

The goal is to investigate the corrosion of stainless steel by lead-bismuth eutectic (LBE), which has been proposed for use as a blanket coolant and a spallation target in the transmuter.

Hydrogen-Induced Embrittlement Of Candidate Target Materials For Applications In Spallation-Neutron-Target Systems, Ajit K. Roy, Brendan O'Toole, Zhiyong Wang, David W. Hatchett

Transmutation Sciences Materials (TRP)

Spallation-neutron-sources, such as those under investigation for use in accelerator-driven transmutation systems, generate neutrons through the collision of high-energy protons, or charged hydrogen atoms, with heavy metal targets such as lead. As a result, these systems also tend to deposit a significant amount of hydrogen in the materials of the transmuter target and superstructure. This can result in accelerated corrosion and changes in the properties of the exposed materials. Of particular importance is a phenomenon called hydrogen embrittlement, in which materials lose their ductility (ability to deform under stress) and become brittle (more susceptible to fracture) after reacting with hydrogen. …

Modeling Corrosion In Oxygen Controlled Lbe Systems With Coupling Of Chemical Kinetics And Hydrodynamics: Task V 4th Quarterly Report, Samir Moujaes

Transmutation Sciences Materials (TRP)

The project is moving on target with the newly realigned objective set for the Phase I. Through close communications with Dr. Li and Dr. Jinsuo Zhang from LANL a realignment of the simulation work has been recommended. The reason for that is the vendor of STAR-CD/CHEMKIN had not perfected yet the final coupling of the post processing of output for any potential surface chemistry reaction taking place on the inside pipe surface of the LBE loop. This is because the coupling of CHEMKIN and STAR-CD has been done fairly recently.

Our final effort has been to generate using an innovative …

Modeling Corrosion In Oxygen Controlled Lbe Systems With Coupling Of Chemical Kinetics And Hydrodynamics, Samir Moujaes, Yitung Chen

Transmutation Sciences Materials (TRP)

Many of the international efforts to develop transmutation technology, including the U.S., Russian, and European scientific communities, have determined that lead bismuth eutectic (LBE) is a potential material for use as a both a spallation target and a coolant. To exploit this potential, a more thorough understanding of the effect and rates of corrosion on steels, particularly non-Russian alloys, inside the LBE systems is required. Properly controlling the oxygen content in LBE systems has been observed to drastically reduce the corrosion of structural steels in LBE. However, the transport of oxygen and formation of corrosion products is not well understood; …

Development Of A Mechanistic Understanding Of High-Temperature Deformation Of Alloy Ep-823, Ajit K. Roy, Brendan O'Toole

Transmutation Sciences Materials (TRP)

Alloy EP-823 has been developed as a structural material for Lead Bismuth Eutectic (LBE) systems, such as those under development for nuclear transmutation systems, as well as other applications. However, very little data regarding the mechanical properties of this alloy exists in the open literature, particularly in the temperature regime of interest for transmutation systems. To address this need, the UNLV research team, in collaboration with researchers from Los Alamos National Laboratory, has developed a research program to evaluate tensile properties of Alloy EP-823 stainless steel at elevated temperatures, which is not being performed at any other facility to date. …

Atomic Hydrogen Cleaning Of Inp(100): Electron Yield And Surface Morphology Of Negative Electron Affinity Activated Surfaces, M. A. Hafez, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Atomic hydrogen cleaning of the InP(100) surface has been investigated using quantitative reflection high-energy electron diffraction. The quantum efficiency of the surface when activated to negative electron affinity was correlated with surface morphology. The electron diffraction patterns showed that hydrogen cleaning is effective in removing surface contaminants, leaving a clean, ordered, and (2×4)-reconstructed surface. After activation to negative electron affinity, a quantum efficiency of ∼6% was produced in response to photoactivation at 632 nm. Secondary electron emission from the hydrogen-cleaned InP(100)-(2×4) surface was measured and correlated to the quantum efficiency. The morphology of the vicinal InP(100) surface was investigated using …

Nitriding Of Titanium By Inductively Coupled Plasma, Abdul Hakim Hashim

Student Works (2000-2009)

A RF planar coil inductively coupled plasma syslem (ICP) is used in this project to nitride a commercially pure titanium substrate. The system is powered by a 600 W, 13.56 MHz, 50 Ω RF generator. The impedance matching is achieved by using an air­-core step-down transformer and a tunable vacuum capacitor. The electrical discharge characteristics of argon and argon-nitrogen admixture plasmas are investigated. Coil current, ion density and RF power transferred in the plasma at different pressure are studied. Nitriding of titanium using the system is found to be able to produce θ-TiN, ε-Ti2N and α-Ti(N) layers, as confirmed by …

Analysis Of Plastics In The Tyre Industry Using Fourier Transform Infrared Techniques, Differential Scanning Calorimetry And Softening Point Apparatus, Ching Ching Loh

Student Works (2000-2009)

The plastics in a tyre factory were investigated. The plastics were analysed by FTlR-transmission, FTI.R-ATR, softening point apparatus as well as a Differential Scanning Calorimeter. All the plastics were detected to be polyethene based with melting point range of 107 to 125°C. It was also observed that The FTIR transmission spectrum can be different from the FTIR-ATR spectrum. The FTIR-ATR spectrum gives a higher band intensity at longer wavelengths compared to the FTIR-Transmission spectrum. Interference fringes can be present in the FTlR transmission spectrum. In addition to the above, it was also found that the melting point of plastics obtained …