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  Partner: UNT Libraries
 Department: Department of Materials Science and Engineering
 Degree Level: Doctoral
 Collection: UNT Theses and Dissertations
Advanced Technology for Source Drain Resistance Reduction in Nanoscale FinFETs

Advanced Technology for Source Drain Resistance Reduction in Nanoscale FinFETs

Date: May 2008
Creator: Smith, Casey Eben
Description: Dual gate MOSFET structures such as FinFETs are widely regarded as the most promising option for continued scaling of silicon based transistors after 2010. This work examines key process modules that enable reduction of both device area and fin width beyond requirements for the 16nm node. Because aggressively scaled FinFET structures suffer significantly degraded device performance due to large source/drain series resistance (RS/D), several methods to mitigate RS/D such as maximizing contact area, silicide engineering, and epitaxially raised S/D have been evaluated.
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Atomistic Simulations of Deformation Mechanisms in Ultra-Light Weight Mg-Li Alloys

Atomistic Simulations of Deformation Mechanisms in Ultra-Light Weight Mg-Li Alloys

Date: May 2015
Creator: Karewar, Shivraj
Description: Mg alloys have spurred a renewed academic and industrial interest because of their ultra-light-weight and high specific strength properties. Hexagonal close packed Mg has low deformability and a high plastic anisotropy between basal and non-basal slip systems at room temperature. Alloying with Li and other elements is believed to counter this deficiency by activating non-basal slip by reducing their nucleation stress. In this work I study how Li addition affects deformation mechanisms in Mg using atomistic simulations. In the first part, I create a reliable and transferable concentration dependent embedded atom method (CD-EAM) potential for my molecular dynamics study of deformation. This potential describes the Mg-Li phase diagram, which accurately describes the phase stability as a function of Li concentration and temperature. Also, it reproduces the heat of mixing, lattice parameters, and bulk moduli of the alloy as a function of Li concentration. Most importantly, our CD-EAM potential reproduces the variation of stacking fault energy for basal, prismatic, and pyramidal slip systems that influences the deformation mechanisms as a function of Li concentration. This success of CD-EAM Mg-Li potential in reproducing different properties, as compared to literature data, shows its reliability and transferability. Next, I use this newly created potential ...
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Barrier and Long Term Creep Properties of Polymer Nanocomposites.

Barrier and Long Term Creep Properties of Polymer Nanocomposites.

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Date: December 2004
Creator: Ranade, Ajit
Description: The barrier properties and long term strength retention of polymers are of significant importance in a number of applications. Enhanced lifetime food packaging, substrates for OLED based flexible displays and long duration scientific balloons are among them. Higher material requirements in these applications drive the need for an accurate measurement system. Therefore, a new system was engineered with enhanced sensitivity and accuracy. Permeability of polymers is affected by permeant solubility and diffusion. One effort to decrease diffusion rates is via increasing the transport path length. We explore this through dispersion of layered silicates into polymers. Layered silicates with effective aspect ratio of 1000:1 have shown promise in improving the barrier and mechanical properties of polymers. The surface of these inorganic silicates was modified with surfactants to improve the interaction with organic polymers. The micro and nanoscale dispersion of the layered silicates was probed using optical and transmission microscopy as well as x-ray diffraction. Thermal transitions were analyzed using differential scanning calorimetry. Mechanical and permeability measurements were correlated to the dispersion and increased density. The essential structure-property relationships were established by comparing semicrystalline and amorphous polymers. Semicrystalline polymers selected were nylon-6 and polyethylene terephthalate. The amorphous polymer was polyethylene terphthalate-glycol. Densification ...
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Biocompatible Hybrid Nanomaterials Involving Polymers and Hydrogels Interfaced with Phosphorescent Complexes and Toxin-Free Metallic Nanoparticles for Biomedical Applications

Biocompatible Hybrid Nanomaterials Involving Polymers and Hydrogels Interfaced with Phosphorescent Complexes and Toxin-Free Metallic Nanoparticles for Biomedical Applications

Date: August 2011
Creator: Marpu, Sreekar B.
Description: The major topics discussed are all relevant to interfacing brightly phosphorescent and non-luminescent coinage metal complexes of [Ag(I) and Au(I)] with biopolymers and thermoresponsive gels for making hybrid nanomaterials with an explanation on syntheses, characterization and their significance in biomedical fields. Experimental results and ongoing work on determining outreaching consequences of these hybrid nanomaterials for various biomedical applications like cancer therapy, bio-imaging and antibacterial abilities are described. In vitro and in vivo studies have been performed on majority of the discussed hybrid nanomaterials and determined that the cytotoxicity or antibacterial activity are comparatively superior when compared to analogues in literature. Consequential differences are noticed in photoluminescence enhancement from hybrid phosphorescent hydrogels, phosphorescent complex ability to physically crosslink, Au(I) sulfides tendency to form NIR (near-infrared) absorbing AuNPs compared to any similar work in literature. Syntheses of these hybrid nanomaterials has been thoroughly investigated and it is determined that either metallic nanoparticles syntheses or syntheses of phosphorescent hydrogels can be carried in single step without involving any hazardous reducing agents or crosslinkers or stabilizers that are commonly employed during multiple step syntheses protocols for syntheses of similar materials in literature. These astounding results that have been discovered within studies of hybrid nanomaterials ...
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Biodegradable Poly(hydroxy Butyrate-co-valerate) Nanocomposites And Blends With Poly(butylene Adipate-co-terephthalate) For Sensor Applications

Biodegradable Poly(hydroxy Butyrate-co-valerate) Nanocomposites And Blends With Poly(butylene Adipate-co-terephthalate) For Sensor Applications

Date: December 2011
Creator: Vidhate, Shailesh.
Description: The utilization of biodegradable polymers is critical for developing “cradle to cradle” mindset with ecological, social and economic consequences. Poly(hydroxy butyrate-co-valerate) (PHBV) shows significant potential for many applications with a polypropylene equivalent mechanical performance. However, it has limitations including high crystallinity, brittleness, small processing window, etc. which need to be overcome before converting them into useful products. Further the development of biodegradable strain sensing polymer sensors for structural health monitoring has been a growing need. In this dissertation I utilize carbon nanotubes as a self sensing dispersed nanofiller. The impact of its addition on PHBV and a blend of PHBV with poly(butylene adipate-co-terephthalate) (PBAT) polymer was examined. Nanocomposites and blends of PHBV, PBAT, and MWCNTs were prepared by melt-blending. The effect of MWCNTs on PHBV crystallinity, crystalline phase, quasi-static and dynamic mechanical property was studied concurrently with piezoresistive response. In PHBV/PBAT blends a rare phenomenon of melting point elevation by the addition of low melting point PBAT was observed. The blends of these two semicrystalline aliphatic and aromatic polyesters were investigated by using differential scanning calorimetry, small angle X-ray scattering, dynamic mechanical analysis, surface energy measurement by contact angle method, polarized optical and scanning electron microscopy, and rheology. The study ...
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Bulk and Interfacial Effects on Density in Polymer Nanocomposites

Bulk and Interfacial Effects on Density in Polymer Nanocomposites

Date: May 2007
Creator: Sahu, Laxmi Kumari
Description: The barrier properties of polymers are a significant factor in determining the shelf or device lifetime in polymer packaging. Nanocomposites developed from the dispersion of nanometer thick platelets into a host polymer matrix have shown much promise. The magnitude of the benefit on permeability has been different depending on the polymer investigated or the degree of dispersion of the platelet in the polymer. In this dissertation, the effect of density changes in the bulk and at the polymer-platelet interface on permeability of polymer nanocomposites is investigated. Nanocomposites of nylon, PET, and PEN were processed by extrusion. Montmorillonite layered silicate (MLS) in a range of concentrations from 1 to 5% was blended with all three resins. Dispersion of the MLS in the matrix was investigated by using one or a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Variation in bulk density via crystallization was analyzed using differential scanning calorimetry (DSC) and polarized optical microscopy. Interfacial densification was investigated using force modulation atomic force microscopy (AFM) and ellipsometry. Mechanical properties are reported. Permeability of all films was measured in an in-house built permeability measurement system. The effect of polymer orientation and induced defects on permeability ...
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Carrier Mobility, Charge Trapping Effects on the Efficiency of Heavily Doped Organic Light-Emitting Diodes, and EU(lll) Based Red OLEDs

Carrier Mobility, Charge Trapping Effects on the Efficiency of Heavily Doped Organic Light-Emitting Diodes, and EU(lll) Based Red OLEDs

Date: August 2010
Creator: Lin, Ming-Te
Description: Transient electroluminescence (EL) was used to measure the onset of emission delay in OLEDs based on transition metal, phosphorescent bis[3,5-bis(2-pyridyl)-1,2,4-triazolato] platinum(ΙΙ) and rare earth, phosphorescent Eu(hfa)3 with 4'-(p-tolyl)-2,2":6',2" terpyridine (ttrpy) doped into 4,4'-bis(carbazol-9-yl) triphenylamine (CBP), from which the carrier mobility was determined. For the Pt(ptp)2 doped CBP films in OLEDs with the structure: ITO/NPB (40nm)/mcp (10nm)/65% Pt(ptp)2:CBP (25nm)/TPBI (30nm)/Mg:Ag (100nm), where NPB=N, N'-bis(1-naphthyl)-N-N'-biphenyl-1, 1'-biphenyl-4, MCP= N, N'-dicarbazolyl-3,5-benzene, TPBI=1,3,5-tris(phenyl-2-benzimidazolyl)-benzene, delayed recombination was observed and based on its dependence on frequency and duty cycle, ascribed to trapping and de-trapping processes at the interface of the emissive layer and electron blocker. The result suggests that the exciton recombination zone is at, or close to the interface between the emissive layer and electron blocker. The lifetime of the thin films of phosphorescent emitter Pt(ptp)2 were studied for comparison with rare earth emitter Eu(hfa)3. The lifetime of 65% Pt(ptp)2:CBP co-film was around 638 nanoseconds at the emission peak of 572nm, and the lifetime of neat Eu(hfa)3 film was obtained around 1 millisecond at 616 nm, which supports the enhanced efficiency obtained from the Pt(ptp)2 devices. The long lifetime and narrow emission of the rare earth dopant Eu(hfa)3 is a fundamental factor limiting device performance. Red ...
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Characterization of Cure Kinetics and Physical Properties of a High Performance, Glass Fiber-Reinforced Epoxy Prepreg and a Novel Fluorine-Modified, Amine-Cured Commercial Epoxy.

Characterization of Cure Kinetics and Physical Properties of a High Performance, Glass Fiber-Reinforced Epoxy Prepreg and a Novel Fluorine-Modified, Amine-Cured Commercial Epoxy.

Date: December 2003
Creator: Bilyeu, Bryan
Description: Kinetic equation parameters for the curing reaction of a commercial glass fiber reinforced high performance epoxy prepreg composed of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM), the tetrafunctional amine curing agent 4,4'-diaminodiphenylsulfone (DDS) and an ionic initiator/accelerator, are determined by various thermal analysis techniques and the results compared. The reaction is monitored by heat generated determined by differential scanning calorimetry (DSC) and by high speed DSC when the reaction rate is high. The changes in physical properties indicating increasing conversion are followed by shifts in glass transition temperature determined by DSC, temperature-modulated DSC (TMDSC), step scan DSC and high speed DSC, thermomechanical (TMA) and dynamic mechanical (DMA) analysis and thermally stimulated depolarization (TSD). Changes in viscosity, also indicative of degree of conversion, are monitored by DMA. Thermal stability as a function of degree of cure is monitored by thermogravimetric analysis (TGA). The parameters of the general kinetic equations, including activation energy and rate constant, are explained and used to compare results of various techniques. The utilities of the kinetic descriptions are demonstrated in the construction of a useful time-temperature-transformation (TTT) diagram and a continuous heating transformation (CHT) diagram for rapid determination of processing parameters in the processing of prepregs. Shrinkage ...
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Charge Interaction Effects in Epoxy with Cation Exchanged Montmorillonite Clay and Carbon Nanotubes.

Charge Interaction Effects in Epoxy with Cation Exchanged Montmorillonite Clay and Carbon Nanotubes.

Date: May 2005
Creator: Butzloff, Peter Robert
Description: The influence of charge heterogeneity in nanoparticles such as montmorillonite layered silicates (MLS) and hybrid systems of MLS + carbon nanotubes was investigated in cured and uncured epoxy. Epoxy nanocomposites made with cation-exchanged montmorillonite clay were found to form agglomerates near a critical concentration. Using differential scanning calorimetry it was determined that the mixing temperature of the epoxy + MLS mixture prior to the addition of the curing agent critically influenced the formation of the agglomerate. Cured epoxy samples showed evidence of the agglomerate being residual charge driven by maxima and minima in the concentration profiles of thermal conductivity and dielectric permittivity respectively. A hybrid nanocomposite of MLS and aniline functionalized multi walled nanotubes indicated no agglomerates. The influence of environmentally and process driven properties on the nanocomposites was investigated by examination of moisture, ultrasound, microwaves and mechanical fatigue on the properties of the hybrid systems. The results point to the importance of charge screening by adsorbed or reacted water and on nanoparticulates.
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Combinatorial Assessment of the Influence of Composition and Exposure Time on the Oxidation Behavior and Concurrent Oxygen-induced Phase Transformations of Binary Ti-x Systems

Combinatorial Assessment of the Influence of Composition and Exposure Time on the Oxidation Behavior and Concurrent Oxygen-induced Phase Transformations of Binary Ti-x Systems

Date: May 2015
Creator: Samimi, Peyman
Description: The relatively low oxidation resistance and subsequent surface embrittlement have often limited the use of titanium alloys in elevated temperature structural applications. Although extensive effort is spent to investigate the high temperature oxidation performance of titanium alloys, the studies are often constrained to complex technical titanium alloys and neither the mechanisms associated with evolution of the oxide scale nor the effect of oxygen ingress on the microstructure of the base metal are well-understood. In addition lack of systematic oxidation studies across a wider domain of the alloy composition has complicated the determination of composition-mechanism-property relationships. Clearly, it would be ideal to assess the influence of composition and exposure time on the oxidation resistance, independent of experimental variabilities regarding time, temperature and atmosphere as the potential source of error. Such studies might also provide a series of metrics (e.g., hardness, scale, etc) that could be interpreted together and related to the alloy composition. In this thesis a novel combinatorial approach was adopted whereby a series of compositionally graded specimens, (Ti-xMo, Ti-xCr, Ti-xAl and Ti-xW) were prepared using Laser Engineered Net Shaping (LENS™) technology and exposed to still-air at 650 °C. A suite of the state-of-the-art characterization techniques were employed to assess ...
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