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Holographic fabrication of 3D photonic crystals through interference of multi-beams with 4 + 1, 5 + 1 and 6 + 1 configurations

Description: This article fabricates 3D photonic crystals or quasi-crystals through single beam and single optical element based holographic lithography.
Date: September 9, 2014
Creator: George, David; Lutkenhaus, Jeffrey; Lowell, David; Moazzezi, Mojtaba; Adewole, Murthada; Philipose, Usha et al.
Partner: UNT College of Arts and Sciences

TEM Studies of Carbon Coated LiFePO4 after Charge DischargeCycling

Description: Carbon coating has proven to be a successful approach toimprove the rate capability of LiFePO4 used in rechargeable Li-ionbatteries. Investigations of the microstructure of carbon coated LiFePO4after charge discharge cycling shows that the carbon surface layerremains intact over 100 cycles. We find micro cracks in the cycledmaterial that extend parallel to low indexed lattice planes. Ourobservations differ from observations made by other authors. However thedifferences between the orientations of crack surfaces in both studiescan be reconciled considering the location of weak bonds in the unit celland specimen geometry as well as elastic stress fields ofdislocation.
Date: November 30, 2006
Creator: Gabrisch, H.; Wilcox, J. & Doeff, M.
Partner: UNT Libraries Government Documents Department

Role of Microstructural Phenomena in Magnetic Thin Films. Final Report

Description: Over the period of the program we systematically varied microstructural features of magnetic thin films in an attempt to better identify the role which each feature plays in determining selected extrinsic magnetic properties. This report summarizes the results.
Date: April 30, 2001
Creator: Laughlin, D. E. & Lambeth, D. N.
Partner: UNT Libraries Government Documents Department

Role of Intergranular Films in Toughened Ceramics

Description: Self-reinforced silicon nitride ceramics rely the generation of elongated grains that act as reinforcing elements to gain increases in fracture toughness. However, the size and number of the reinforcing grains must be controlled, along with the matrix grain size, to optimize the fracture toughness and strength. Furthermore, the toughening processes of crack bridging are dependent upon retention of these reinforcing grains during crack extension by an interfacial debonding process. Both the debonding process and the resultant toughening effects are found to be influenced by the composition of the sintering aids which typical are incorporated into the amorphous intergranular films found in these ceramics. Specifically, it is shown that the interface between the intergranular glass and the reinforcing grains is strengthened in the presence of an epitaxial SiAlON layer. In addition, the interface strength increases with the Al and 0 content of the SiAlON layer. Micromechanics modeling indicates that stresses associated with thermal expansion mismatch are a secondary factor in interfacial debonding in these specific systems. On the other hand, first principles atomic cluster calculations reveal that the debonding behavior is consistent with the formation of strong Si-0 and Al-O bonds across the glass-crystalline interface.
Date: May 10, 1999
Creator: Becher, P.F.; Hsueh, C.H.; More, K.L.; Painter, G.S. & Sun, E.Y.
Partner: UNT Libraries Government Documents Department

Interfacial Microstructure Formed by Reactive Metal Penetration of Al into Mullite

Description: Microstructure in the reaction interface between molten Al and dense mullite have been studied by transmission electron microscopy to provide insight into mechanisms for forming ceramic-metal composites by reactive metal penetration. The reactions, which have the overall stoichiometry, 3Al#iz01~ + (8+ x)A1 + 13 AlzO~ + xA1 + 6Si, were carried out at temperatures of 900, 1100, and 1200oC for 5 minutes and 60 minutes, and 1400oC for 15 minutes. Observed phases generally were those given in the above reaction, although their proportions and interracial rnicrostructures differed strongly with reaction temperature. After reaction at 900oC, a thin Al layer separated unreacted mullite from the cx-AlzO~ and Al reaction products. No Si phase was found near the reaction front. After 5 minutes at 1100"C, the nxtction front contained Si, ct-A120~, and an aluminum oxide phase with a high concentration of Si. After 60 minutes at 11O(YC many of the cx-A120g particles were needle-shaped with a preferred orientation. After reaction at 1200oC, the reaction front contained a high density of Si particles that formed a continuous layer over many of the mullite grains. The sample reacted at 140VC for 15 minutes had a dense ct-A120J reaction layer less than 2~m thick. Some isolated Si particles were present between the a-AlzO~ layer and the unreacted mullite. Using previously measured reaction kinetics data, the observed temperature dependence of the interracial microstructure have been modeled as three sequential steps, each one of which is rate-limiting in a different temperature range.
Date: April 27, 1999
Creator: Du, T.B.; Ewsuk, K.G.; Fahrenholtz, W.G.; Loehman, R.E. & Lu, P.
Partner: UNT Libraries Government Documents Department

Self-Organized Vertical Superlattices in Epitaxial GaInAsSb

Description: Self-organized superlattices are observed in GaInAsSb epilayers grown nominally lattice matched to vicinal GaSb substrates. The natural superlattice (NSL) is detected at the onset of growth; is continuous over the lateral extent of over several microns; and persists vertically throughout several microns of the epilayer. Furthermore, the NSL is inclined by an additional 4{sup o} with respect to the vicinal (001) GaSb substrate. The tilted NSL intersects the surface of the epilayer, and the NSL period is geometrically correlated with surface undulations. While the principle driving force for this type of phase separation arises from solution thermodyamics, the mechanism for the self-organized microstructure is related to local strains associated with surface undulations. By using a substrate with surface undulations, the tilted NSL can be induced in layers with alloy compositions that normally do not exhibit this self-organized microstructure under typical growth conditions. These results underscore the complex interactions between compositional modulations and morphological perturbations.
Date: February 9, 2004
Creator: Wand, CA; Vineis, CJ & Calawa, DR
Partner: UNT Libraries Government Documents Department

Structure and elevated temperature properties of ferritic alloys strengthened by intermetallic compounds

Description: Thesis. An investigation was conducted to develop high-temperature 1Ta-- 6Cr, 1Ta--7Cr, and 1Ta-7Cr--0.5 Mo alloys using a dispersion of the Laves phase in a noncarbon-containing, body-centeredcubic iron matrix. An understanding and application of basic principles of materials science and the use of large amounts of information available in the literature were instrumental in the development of Fe-- Ta-- Cr alloys of the investigation. The phase transformations that occurred in the alloys, and the resulting microstructures were studied. The relations between mechanical properties and structure were also examined. Short- time tensile mechanical properties and long-time creep and stress-rupture tests were conducted on the alloys in which microstructural features were varied by changes in the heat-treating procedure. The mechanical properties were compared with those of several commercially available steels. An examination of substructure and precipitate distribution of the alloys before and after creep tests, the determination of apparent activation energy for creep, and an estimation of the stress sensitivity of steady-state creep rates were carried out in order to investigate the mechanism of creep in dispersion-hardened ferritic alloys. Fracture surface morphology was examined after specimens were tested in short-time tension and in creep. (JRD)
Date: September 1, 1973
Creator: Bhandarkar, M.D.
Partner: UNT Libraries Government Documents Department

A hierarchical framework for the multiscale modeling of microstructure evolution in heterogeneous materials.

Description: All materials are heterogeneous at various scales of observation. The influence of material heterogeneity on nonuniform response and microstructure evolution can have profound impact on continuum thermomechanical response at macroscopic “engineering” scales. In many cases, it is necessary to treat this behavior as a multiscale process thus integrating the physical understanding of material behavior at various physical (length and time) scales in order to more accurately predict the thermomechanical response of materials as their microstructure evolves. The intent of the dissertation is to provide a formal framework for multiscale hierarchical homogenization to be used in developing constitutive models.
Date: April 1, 2010
Creator: Luscher, Darby J.
Partner: UNT Libraries Government Documents Department

Metallurgy and Ceramics/Superplasticity in Metals and Ceramics

Description: In the past three years, we have carried out a number of studies on the deformation and superplasticity of fine-structured materials. The goal was to develop an understanding on the deformation microstructure relationship in these advanced materials and to improve further their properties through microstructural control. In this report, we describe only some of the key results and observations from these studies.
Date: February 6, 2002
Creator: Nieh, T G
Partner: UNT Libraries Government Documents Department

Structure and Properties of Nanoparticles Formed by Ion Implantation

Description: This chapter broadly describes the formation, basic microstructure, and fundamental optoelectronic properties of nanocomposites synthesized by ion implantation. It is not meant as a complete literature survey and by no means includes all references on a subject that has seen a considerable amount of research effort in the past 15 years. However, it should be a good starting point for those new to the field and in a concise way summarize the main lines of research by discussing the optical, magnetic, and smart properties of these nanoparticles and the dependence of these properties on the overall microstructure. The chapter concludes with an outlook for the future.
Date: January 1, 2009
Creator: Meldrum, A.; Lopez, R.; Magruder, R H; Boatner, Lynn A & White, Clark W
Partner: UNT Libraries Government Documents Department

Crystal structure of kappa-In2Se3

Description: Structural properties of single-phase films of {kappa}-In{sub 2}Se{sub 3} and {gamma}-In{sub 2}Se{sub 3} were investigated. Both films were polycrystalline but their microstructure differed considerably. The a-lattice parameter of {kappa}-In{sub 2}Se{sub 3} has been measured. Comparison between these two materials indicates that {kappa}-In{sub 2}Se{sub 3} has a significantly larger unit cell ({Delta}c = 2.5 {+-} 0.2 % and {Delta}a = 13.5 {+-} 0.5%) and a structure more similar to the {alpha}-phase of In{sub 2}Se{sub 3}.
Date: October 24, 2002
Creator: Jasinski, J.; Swider, W.; Washburn, J.; Liliental-Weber, Z.; Chaiken, A.; Nauka, K. et al.
Partner: UNT Libraries Government Documents Department

Multiscale Simulation of Thermo-mechanical Processes in Irradiated Fission-reactor Materials

Description: This report contains a summary of progress made on the subtask area on phase field model development for microstructure evolution in irradiated materials, which was a part of the Computational Materials Science Network (CMSN) project entitled: Multiscale Simulation of Thermo-mechanical Processes in Irradiated Fission-reactor Materials. The model problem chosen has been that of void nucleation and growth under irradiation conditions in single component systems.
Date: May 28, 2012
Creator: El-Azab, Anter
Partner: UNT Libraries Government Documents Department

Investigating the performance of catalyst layer micro-structures with different platinum loadings

Description: In this study a four-phase micro-structure of a PEFC catalyst layer was reconstructed by randomly placing overlapping spheres for each solid catalyst phase. The micro-structure was mirrored to make a micro-structure. A body-fit computational mesh was produced for the reconstructed micro-structure in OpenFOAM. Associated conservation equations were solved within all the phases with electrochemical reaction as the boundary condition at the interface between ionomer and platinum phases. The study is focused on the platinum loading of CL. The polarization curves of the micro-structure performance have been compared for different platinum loadings. This paper gives increased insight into the relatively greater losses at decreased platinum loadings.
Date: July 1, 2012
Creator: Khakaz-Baboli, Moben; Harvey, David & Pharoah, Jon
Partner: UNT Libraries Government Documents Department

Thermal modification of microstructures and grain boundaries in silicon carbide

Description: Polycrystalline SiC samples hot-pressed with aluminum, boron, and carbon sintering additions (ABC-SiC) were characterized using transmission electron microscopy. The study focused on the effects of high temperature treatment on microstructure.
Date: May 23, 2003
Creator: Zhang, Xiao Feng & De Jonghe, Lutgard C.
Partner: UNT Libraries Government Documents Department

Microstructure and thermal stability of transition metal nitrides and borides on GaN

Description: Microstructure and thermal stability of ZrN/ZrB2 bilayer deposited on GaN have been studied using transmission electron microscopy methods (TEM) and secondary ion mass spectrometry (SIMS). It has been demonstrated that annealing of the contact structure at 1100 C in N2 atmosphere does not lead to any observable metal/ semiconductor interaction. In contrast, a failure of the integrity of ZrN/ZrB2 metallization at 800 C, when the heat treatment is performed in O2 ambient has been observed.
Date: June 28, 2000
Creator: Jasinski, J.; Kaminska, E.; Piotrowska, A.; Barcz, A. & Zielinski, M.
Partner: UNT Libraries Government Documents Department