Materials Science and Engineering Commons^™

Electron Effective Mass And Phonon Modes In Gaas Incorporating Boron And Indium, Tino Hofmann, Mathias Schubert, G. Leibiger, V. Gottschalch

Materials Research Science and Engineering Center: Faculty Publications

The strain-free boron- and indium-containing GaAs compounds are promising candidates for III-V semiconductor solar cell absorber materials with lattice match to GaAs, for which experimental data of the electronic band structure are widely unknown. For nondegenerate, silicon-doped, n-type B_0.03In_0.06Ga_0.91As with band-gap energy of 1.36 eV, determined by near-infrared ellipsometry, a strong increase of the electron effective mass of 44% in B0.03In0.06Ga0.91As compared to In_0.06Ga_0.94As is obtained from far-infrared magneto-optic generalized ellipsometry studies. The authors thereby obtain the vibrational lattice mode behavior. For BAs, an experimentally obscure compound, the curvature …

Surface Modification Of 6h-Sic Under Vacuum Annealing Studied By Time Of Flight Positron Annihilation Induced Auger Electron Spectroscopy, Saurabh Mukherjee

Material Science and Engineering Theses - Archive

This thesis presents the first study of vacuum annealing of 6H- SiC surface using Time-of-Flight-Positron Annihilation induced Auger Electron Spectroscopy(TOF-PAES) . The study was the first application of a TOF-PAES spectrometer to the SiC. The increased efficiency of the TOF-PAES allows us to see simultaneously for the first time Si-LVV, C-KVV, O-KVV peaks in the PAES spectrum for SiC. The top layer surface concentrations of C, O and Si were monitored by TOF-PAES surface. The results indicate that the SiC surface was initially covered with a layer containing oxygen but largely devoid of Si which was subsequently removed as a …

Dimesionality Aspects Of Nano Micro Integrated Metal Oxide Based Early Stage Leak Detection Room Temperature Hydrogen Sensor, Sameer Arun Deshpande

Electronic Theses and Dissertations

Detection of explosive gas leaks such as hydrogen (H2) becomes key element in the wake of counter-terrorism threats, introduction of hydrogen powered vehicles and use of hydrogen as a fuel for space explorations. In recent years, a significant interest has developed on metal oxide nanostructured sensors for the detection of hydrogen gas. Gas sensors properties such as sensitivity, selectivity and response time can be enhanced by tailoring the size, the shape, the structure and the surface of the nanostructures. Sensor properties (sensitivity, selectivity and response time) are largely modulated by operating temperature of the device. Issues like instability of nanostructures …

Mechanisms Of Lifetime Improvement In Thermal Barrier Coatings With Hf And/Or Y Modification Of Cmsx-4 Superalloy Substrates, Jing Liu

Electronic Theses and Dissertations

In modern turbine engines for propulsion and energy generation, thermal barrier coating (TBCs) protect hot-section blades and vanes, and play a critical role in enhancing reliability, durability and operation efficiency. In this study, thermal cyclic lifetime and microstructural degradation of electron beam physical vapor deposited (EB-PVD) Yttria Stabilized Zirconia (YSZ) with (Ni,Pt)Al bond coat and Hf- and/or Y- modified CMSX-4 superalloy substrates were examined. Thermal cyclic lifetime of TBCs was measured using a furnace thermal cycle test that consisted of 10-minute heat-up, 50-minute dwell at 1135C, and 10-minute forced-air-quench. TBC lifetime was observed to improve from 600 cycles to over …

The Effect Of The Rate Of Precursor Production On The Purity And Aggregation Morphology Of Nanoparticulate Zinc Oxide, Grainne Duffy, Suresh Pillai, Declan Mccormack

Articles

The synthesis of zinc oxide through the decomposition of a solid oxalate precursor was
investigated. It was found that the rate of preparation of the precursor had a quantitative effect on
the morphology and extent of surface ligation of particles produced; contrary to our expectations,
it was found that the slow combination of reagents led to a less pure product. It has been
determined that this time dependence mimics the variation of reactant ratios. Zinc oxide particles
were produced from a number of reactant ratios, and were characterised by TEM, XRD, FT-IR
and DSC. It was found that the size …

Growth Of Mc3t3-El Pre-Osteoblasts On Borate Containing Glasses & Growth Of Osteoblastic Cells On 13-93 Glass Scaffolds, Agatha Dwilewicz

Opportunities for Undergraduate Research Experience Program (OURE)

Three borate-based glasses, compositions designated 1B, 2B, and 3B, with B₂0₃ levels of 15, 31, and 46 mole percent (Table 1), respectively, were tested for their effects on the growth of MC3T3-El mouse pre-osteoblastic cells under physiological fluid conditions. Silicate type 45S5 glass was used as a control for comparison. Independently, the biocompatibility of recently developed silicate-based porous 13-93 bioactive glass scaffolds was tested; Saos-2 human osteosarcoma cell line was used. Tests performed for the two studies included: contact assays of cell growth at the glass interface, chemical analysis of borate released into the culture medium, quantitative …

Processing And Study Of Carbon Nanotube / Polymer Nanocomposites And Polymer Electrolyte Materials, Muthuraman Harish

Electronic Theses and Dissertations

The first part of the study deals with the preparation of carbon nanotube/polymer nanocomposite materials. The dispersion of multi-walled carbon nanotubes (MWNTs) using trifluoroacetic acid (TFA) as a co-solvent and its subsequent use in polymer nanocomposite fabrication is reported. The use of carbon nanotube/ polymer nanocomposite system for the fabrication of organic solar cells is also studied. TFA is a strong but volatile acid which is miscible with many commonly used organic solvents. Our study demonstrates that MWNTs can be effectively purified and readily dispersed in a range of organic solvents including dimethyl formamide (DMF), tetrahydrofuran (THF), and dichloromethane when …

Low Temperature Nitife Shape Memory Alloys: Actuator Engineering And Investigation Of Deformation Mechanisms Using In Situ Neutr, Vinu Krishnan

Electronic Theses and Dissertations

Shape memory alloys are incorporated as actuator elements due to their inherent ability to sense a change in temperature and actuate against external loads by undergoing a shape change as a result of a temperature-induced phase transformation. The cubic so-called austenite to the trigonal so-called R-phase transformation in NiTiFe shape memory alloys offers a practical temperature range for actuator operation at low temperatures, as it exhibits a narrow temperature-hysteresis with a desirable fatigue response. Overall, this work is an investigation of selected science and engineering aspects of low temperature NiTiFe shape memory alloys. The scientific study was performed using in …

Vacancy Engineered Doped And Undoped Nanocrystalline Rare Earth Oxide Particles For High Temperature Oxidation Resistant Coating, Ranjith Thanneeru

Electronic Theses and Dissertations

Rare earth oxides with trivalent lattice dopants have been of great interest to researchers in the recent years due to its potential applications in catalysis and high temperature protective coatings. The ability to store oxygen in rare earths is the basis for catalysis because of the ability to change valence states which causes the presence of intrinsic oxygen vacancies in the crystal lattice. Although, several doped-rare earth oxide systems in micron scale have been investigated, the doping effect in cerium oxide nanoparticles with well characterized particle size has not been studied. The doping of ceria at that small size can …

The Effect Of The Size Of Pinning Centres On The Critical Current Density In High-Temperature Superconductors, Salama Bakhit Sowaidan Al-Neaimi

Theses

Superconductor materials that have no resistance to the flow of electricity are one of the last great frontiers of scientific discovery.

Superconductivity in these materials occurs particularly in the copper-oxide (CuO₂) planes. However, since these materials are type-II superconductors, magnetic fields can penetrate these materials in quantized amounts of flux called vortices without completely destroying superconductivity, but producing some resistance, due to vortex motion. In order to overcome the resistance problem, vortices must be pinned to prevent their motion and hence eliminate the resistance.

In this work study we have performed extensive numerical simulations to study the effect …

Increasing Energy Efficiency Through Improvements In Ladle Materials And Practices, Kent D. Peaslee, Semen Naumovich Lekakh, Jeffrey D. Smith, Mangesh Vibhandik

Materials Science and Engineering Faculty Research & Creative Works

Steel foundry ladle practices play an important role in total energy efficiency of melting as well as influence casting quality. Extensive heat losses in the ladle could be associated with excessive superheating of the melt before tap which increases energy consumption, promotes oxidation of the melt and increases refractory consumption. A high cooling rate of the liquid metal in the ladle could also cause casting quality instability. The overall ladle heat balance and components of heat losses were analyzed using FLUENT and FACTSAGE software and validated with experimental data from both the UMR foundry and industrial foundries. The purpose of …

Preparation Of Bioactive Glasses With Controllable Degradation Behavior And Their Bioactive Characterization, Aihua Yao, Deping Wang, Qiang Fu, M. N. Rahaman, Wen-Hai Huang

Materials Science and Engineering Faculty Research & Creative Works

Bioactive glasses and ceramics have been widely investigated for bone repair because of their excel-lent bioactive characteristics. However, these biomaterials undergo incomplete conversion into a bone-like material, which severely limits their biomedical application. In this paper, borosilicate bioac-tive glasses were prepared by traditional melting process. The results showed that borosilicate glasses possessed high biocompatibility and bioactivity. In addition, when immersed in a 0.02 mol/L K2HPO4 solution, particles of a borate glass were fully converted to HA. The desirable conversion rate to HA may be achieved through the adjustment of the B2O3/SiO2 ratio. The results of XRD and FTIR analysis indicated …

Iii Finishing, Lapping, Honing And Polishing: Processes, Characterisation And Novel Techniques-Experimental Research On Ultra-Smooth Surface Polishing Based On Two-Dimensional Vibration Of Liquid, Zhong Ning Guo, X. Z. Huang, Z. G. Huang, Z. Q. Yu, T. M. Yue, Wing Bun Lee

Faculty Publications

No abstract provided.

Dielectric Anisotropy And Phonon Modes Of Ordered Indirect-Gap Al0.52In0.48P Studied By Far-Infrared Ellipsometry, Tino Hofmann, V. Gottschalch, Mathias Schubert

Materials Research Science and Engineering Center: Faculty Publications

The infrared (100–600 cm⁻¹) optical properties of partially CuPt-type ordered Al_0.52In_0.48P deposited lattice matched on GaAs are studied by ellipsometry. The authors determine the ordinary and extraordinary dielectric functions and report on the evolution of the optical phonon mode frequencies of Al_0.52In_0.48P as a function of the degree of ordering. In addition to the InP- and AlP-like phonon modes, they observe two alloy-induced phonon modes which are anisotropic upon CuPt ordering. The observed modes are associated to vibrations with E and A₁ symmetries. The alloy-induced phonon modes are useful …

Demonstration Of An Ultraviolet Zno-Based Optically Pumped Third Order Distributed Feedback Laser, Daniel Hofstetter, Yargo Bonetti, Fabrizio Giorgetta, Abdel-Hamid El-Shaer, Andrey Bakin, Andreas Waag, Rudiger Schmidt-Grund, Mathias Schubert, Marius Grundmann

Materials Research Science and Engineering Center: Faculty Publications

The authors demonstrate an optically pumped ZnO distributed feedback laser operating at 383 nm. For a large temperature range between 10 and 270 K, the device lased in a single longitudinal mode. Mode selection was accomplished via a third order diffraction grating, which was dry etched into a 120 nm thick Si₃N₄ layer deposited on the ZnO active region. They observed a spectral linewidth of 0.4 nm, a pump threshold intensity of 0.12 MW/cm², and a peak output power of 14 mW. From wavelength versus temperature measurements, they deduced a temperature tuning coefficient of the …

Creating Micro- And Nanostructures On Tubular And Spherical Surfaces, O. Lima, L. Tan, A. Goel, Mehrdad Negahban, Z. Li

Materials Research Science and Engineering Center: Faculty Publications

The authors developed a new technique to create micro- and nanometer scale structures on curved free-standing objects by combining embossing/imprinting lithography approaches with mechanical loadings on elastic films. Embossing/imprinting generates small structures and mechanical loading determines shape or geometry of the final object. As a result, a portion of the tubes with a radius between 0.5 and 3.5 mm and a portion of the spheres with a radius between 2.4 and 7.0 mm were fabricated with grating line features (period of 700 nm) and microlens array features (lens radius of 2.5 µm) atop, respectively. It was found that both static …

Dielectric Constants And Phonon Modes Of Amorphous Hafnium Aluminate Deposited By Metal Organic Chemical Vapor Deposition, C. Bundesmann, O. Buiu, S. Hall, Mathias Schubert

Materials Research Science and Engineering Center: Faculty Publications

Dielectric constants and long-wavelength optical phonon modes of amorphous hafnium aluminate films with a maximum aluminum content of 19 at. % are studied by infrared spectroscopic ellipsometry (IRSE). The hafnium aluminate films were prepared by metal organic chemical vapor deposition on silicon substrates. IRSE revealed one polar lattice mode and one impurity-type mode, which show all a systematic shift in frequency with varying Al content. The static dielectric constant decreases from 10.1 for 4.6 at. % Al to 8.1 for 19 at. % Al. The absolute values were found to be between 50% and 70% smaller than the values obtained …

Sequential Stretching Lithography, Haojing Lin, Ocelio V. Lima, Li Tan, Zheng Li, Jiangyu Li

Materials Research Science and Engineering Center: Faculty Publications

We developed an embossing/imprinting based nanofabrication technique, dubbed sequential stretching lithography (SSL). In this process, a master pattern is imprinted into an elastomer containing a film of uncured elastomer. The elastomer is cured and then elongated to increase feature density and reduce feature size. Replication of this substrate yields a new master that can be used in further reduction steps. One-dimensional grating features with a pitch size below 200 nm were fabricated from 750 nm-pitch grating lines. This process gives us a faithful pattern miniaturization in all aspects and, as a result, a much effective control on density and dimension …

Nonvolatile Two-Terminal Molecular Memory, Jason Snodgrass, Glen Kennedy, Wai-Ning Mei, Renat F. Sabirianov

Materials Research Science and Engineering Center: Faculty Publications

We propose a nonvolatile two-terminal memory device with two resistance states based on the molecular tunnel junctions. This tunnel junction is composed of one or a few monolayers of polar molecules sandwiched between two electrodes made of materials with different screening length. As a prototype model system we study a rare earth endohedral metallofullerene molecule with reversible dipole moment sandwiched between metal and semiconducting electrodes, forming a double barrier junction. We use the Thomas-Fermi model to calculate the potential profile across the device. Calculated tunneling conductance through the proposed structure changes by order of magnitude upon the reversal of the …

Influence Of Van Der Waals Forces On Increasing The Strength And Toughness In Dynamic Fracture Of Nanofibre Networks: A Peridynamic Approach, Florin Bobaru Ph.D.

Department of Engineering Mechanics: Faculty Publications

The peridynamic method is used here to analyse the effect of van der Waals forces on the mechanical behaviour and strength and toughness properties of three-dimensional nanofibre networks under imposed stretch deformation. The peridynamic formulation allows for a natural inclusion of long-range forces (such as van der Waals forces) by considering all interactions as ‘long-range’. We use van der Waals interactions only between different fibres and do not need to model individual atoms. Fracture is introduced at the microstructural (peridynamic bond) level for the microelastic type bonds, while van der Waals bonds can reform at any time. We conduct statistical …

Capillary Flow Analysis And Computation Of De-Wetting And Wetting Resistances In Angular Geometries, Daniel Bolleddula

Dissertations and Theses

Capillary flows in containers or conduits with interior corners are commonplace in nature and industry. The majority of investigations addressing such flows solve the problem numerically in terms of a flow resistance coefficient (friction factor) for cases where spontaneous liquid spreading along the corner occurs for contact angles below the Concus-Finn critical wetting condition for the particular conduit geometry of interest. This research effort provides missing numerical data for the flow resistance function F_i for partially wetting systems above the Concus-Finn condition. In such cases the fluid spontaneously de-wets the interior corner and often retracts into corner-bound drops. A …

Fracture Toughness Of Ceramic Moulds For Investment Casting With Ice Patterns, Qingbin Liu, Ming-Chuan Leu, Von Richards

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Ice patterns can be used to make ceramic investment moulds for metal castings. Owing to the characteristics of ice, the ceramic mould must be made at subzero temperatures and consequently, requires a different formulation than shells built at room temperature. Success of this process depends greatly on the fracture toughness of mould materials. The present paper describes the experimental results of fracture toughness of mould materials processed from different compositions. The Taguchi method was used to reduce the trial runs. The parameters considered included the ratio of fibre containing fused silica and aluminosilicate powders, the volume of binder and the …

Thermal Conductivity Improvement In Carbon Nanoparticle Doped Pao Oil: An Experimental Study, Shadab Shaikh, Khalid Lafdi, Rengasamy Ponnappan

Chemical and Materials Engineering Faculty Publications

The present work involves a study on the thermal conductivity of nanoparticle-oil suspensions for three types of nanoparticles, namely, carbon nanotubes(CNTs), exfoliated graphite (EXG), and heat treated nanofibers (HTT) with PAO oil as the base fluid. To accomplish the above task, an experimental analysis is performed using a modern light flash technique (LFA 447) for measuring the thermal conductivity of the three types of nanofluids, for different loading of nanoparticles.

The experimental results show a similar trend as observed in literature for nanofluids with a maximum enhancement of approximately 161% obtained for the CNT-PAO oil suspension. The overall percent enhancements …

Experimental Study On The Influence Of Foam Porosity And Pore Size On The Melting Of Phase Change Materials, Khalid Lafdi, Osama Mesalam Mesalhy, Shadab Shaikh

Chemical and Materials Engineering Faculty Publications

Experimental study was carried out to study the phase change heat transfer within a composite of phase change material (PCM) infiltrated high thermal conductivity foam. An experimental setup was built to measure the temperature profiles and capture the melting evolution of the PCM inside aluminum foams. Aluminum foams were used as the porous material, and low melting temperature paraffin wax was used as the PCM. It was observed from the results that the system parameters of the wax/foam composite had a significant influence on its heat transfer behavior.

By using higher porosity aluminum foam, the steady-state temperature was reached faster …

Effect Of Carbon Nanofiber Heat Treatment On Physical Properties Of Polymeric Nanocomposites—Part I, Khalid Lafdi, William Fox, Matthew Matzek, Emel Yildiz

Chemical and Materials Engineering Faculty Publications

The definition of a nanocomposite material has broadened significantly to encompass a large variety of systems made of dissimilar components and mixed at the nanometer scale. The properties of nanocomposite materials also depend on the morphology, crystallinity, and interfacial characteristics of the individual constituents. In the current work, vapor-grown carbon nanofibers were subjected to varying heat-treatment temperatures.

The strength of adhesion between the nanofiber and an epoxy (thermoset) matrix was characterized by the flexural strength and modulus. Heat treatment to 1800C∘ demonstrated maximum improvement in mechanical properties over that of the neat resin, while heat-treatment to higher temperatures demonstrated a …

Understanding The Low Temperature Electrical Propertiesof Nanocrystalline Sno2 For Gas Sensor Applications, Christina Drake

Electronic Theses and Dissertations

Nanocrystalline metal/metal oxide is an important class of transparent and electronic materials due to its potential use in many applications, including gas sensors. At the nanoscale, many of the phenomena observed that give nanocrystalline semiconducting oxide enhanced performance as a gas sensor material over other conventional engineering materials is still poorly understood. This study is aimed at understanding the low temperature electrical and chemical properties of nanocrystalline SnO2 that makes it suitable for room temperature gas detectors. Studies were carried out in order to understand how various synthesis methods affect the surfaces on the nano-oxides, interactions of a target gas …

Plasma Processing For Retention Of Nanostructures, Viswanathan Venkatachalapathy

Electronic Theses and Dissertations

Plasma spray processing is a technique that is used extensively in thermal barrier coatings on gas and steam turbine components, biomedical implants and automotive components. Many processing parameters are involved to achieve a coating with certain functionality. The coating could be required to function as thermal barrier, wear resistant, corrosion resistant or a high temperature oxidation resistant coating. Various parameters, such as, nozzle and electrode design, powder feeding system, spray distances, substrate temperature and roughness, plasma gas flow rates and others can greatly alter the coating quality and resulting performance. Feedstock (powder or solution precursor) composition and morphology are some …

Mode Suppressed Tem Cell Design For High Frequency Ic Measurements, Shaowei Deng, David Pommerenke, Todd H. Hubing, James L. Drewniak, Daryl G. Beetner, Dongshik Shin, Sungnam Kim, Hocheol Kwak

Electrical and Computer Engineering Faculty Research & Creative Works

TEM cells or GTEM cells can be used to evaluate the radiated emissions of integrated circuits (ICs). The applicable frequency bandwidth of a TEM cell is limited due to the resonances of higher order modes. This paper describes how a TEM cell can be modified to extend the frequency range without changing the test topology. Several methods are proposed and implemented to suppress the higher order modes. The magnetic field coupling and electric field coupling are evaluated for the new design. The frequency bandwidth of the modified TEM cell is extended from original 1 GHz to 2.5 GHz.

Irradiation And Metal-Containing Conjugated-Polymer Nanocomposites, Frank D. Blum, Zhe-Fei Li, Sunil K. Pillalamarri, Massimo F. Bertino

Chemistry Faculty Research & Creative Works

In recent years, there has been considerable interest in inorganic/organic hybrid materials that combine the desirable properties of both classes. These composite materials may find significant application in a variety of applications such as sensors, memory and energy conversion, to name just a few. In our laboratories, we have recently made a series of studies on the production of polymer nanofibers and their composites with nanometals. Much of this work has focused on the production of polyaniline (PANI) nanofibers that have been made from one-pot syntheses in aqueous solutions where the polymerization was influenced by -radiation1 or UV-radiation.2 in the …

Development And Application Of A High-Resolution Thin-Film Probe, Shaohua Li, Kuifeng Hu, Daryl G. Beetner, James L. Drewniak, James N. Reck, Matthew O'Keefe, Kai Wang, Xiaopeng Dong, Kevin P. Slattery

Electrical and Computer Engineering Faculty Research & Creative Works

This paper documents the development, characterization, and application of a high-resolution thin-film magnetic-field probe. Probe diameter ranged from 5-μm to 100-μm. The 100-μm probe exhibits a 250-7μm improvement in spatial resolution compared to a conventional loop probe, measured at a height of 250 μm over differential traces with a 118-μm spacing. Electric field rejection was improved using shielding and using a 180-degree hybrid junction to separate common-mode (electric field) and differential-mode (primarily magnetic field) coupling. A network analyzer with narrow band filtering was used to detect the relatively weak signal from the probe and to allow detection of phase information. …