You limited your search to:

 Department: Department of Materials Science and Engineering
 Degree Level: Master's
 Collection: UNT Theses and Dissertations
Effect of Silyation on Organosilcate Glass Films

Effect of Silyation on Organosilcate Glass Films

Access: Use of this item is restricted to the UNT Community.
Date: August 2004
Creator: Kadam, Poonam
Description: Photoresist stripping with oxygen plasma ashing destroys the functional groups in organosilicate glass films and induce moisture uptake, causing low-k dielectric degradation. In this study, hexamethyldisilazane (HMDS), triethylchlorosilane and tripropylchlorosilane are used to repair the damage to organosilicate glass by the O2 plasma ashing process. The optimization of the surface functionalization of the organosilicate glass by the silanes and the thermal stability of the functionalized surfaces are investigated. These experimental results show that HMDS is a promising technique to repair the damage to OSG during the photoresist removal processing and that the heat treatment of the functionalized surfaces causes degradation of the silanes deteriorating the hydrophobicity of the films.
Contributing Partner: UNT Libraries
Evaluation of hydrogen trapping in HfO2 high-κ dielectric thin films.

Evaluation of hydrogen trapping in HfO2 high-κ dielectric thin films.

Access: Use of this item is restricted to the UNT Community.
Date: August 2006
Creator: Ukirde, Vaishali
Description: Hafnium based high-κ dielectrics are considered potential candidates to replace SiO2 or SiON as the gate dielectric in complementary metal oxide semiconductor (CMOS) devices. Hydrogen is one of the most significant elements in semiconductor technology because of its pervasiveness in various deposition and optimization processes of electronic structures. Therefore, it is important to understand the properties and behavior of hydrogen in semiconductors with the final aim of controlling and using hydrogen to improve electronic performance of electronic structures. Trap transformations under annealing treatments in hydrogen ambient normally involve passivation of traps at thermal SiO2/Si interfaces by hydrogen. High-κ dielectric films are believed to exhibit significantly higher charge trapping affinity than SiO2. In this thesis, study of hydrogen trapping in alternate gate dielectric candidates such as HfO2 during annealing in hydrogen ambient is presented. Rutherford backscattering spectroscopy (RBS), elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA) were used to characterize these thin dielectric materials. It was demonstrated that hydrogen trapping in bulk HfO2 is significantly reduced for pre-oxidized HfO2 prior to forming gas anneals. This strong dependence on oxygen pre-processing is believed to be due to oxygen vacancies/deficiencies and hydrogen-carbon impurity complexes that originate from organic precursors used in ...
Contributing Partner: UNT Libraries
First Principle Calculations of the Structure and Electronic Properties of Pentacene Based Organic and ZnO Based Inorganic Semiconducting Materials

First Principle Calculations of the Structure and Electronic Properties of Pentacene Based Organic and ZnO Based Inorganic Semiconducting Materials

Date: May 2012
Creator: Li, Yun
Description: In this thesis, I utilize first principles density functional theory (DFT) based calculations to investigate the structure and electronic properties including charge transfer behaviors and work function of two types of materials: pentacene based organic semiconductors and ZnO transparent conducting oxides, with an aim to search for high mobility n-type organic semiconductors and fine tuning work functions of ZnO through surface modifications. Based on DFT calculations of numerous structure combinations, I proposed a pentacene and perfluoro-pentacene alternating hybrid structures as a new type of n-type semiconductor. Based on the DFT calculations and Marcus charge transfer theory analysis, the new structure has high charge mobility and can be a promising new n-type organic semiconductor material. DFT calculations have been used to systematically investigate the effect of surface organic absorbate and surface defects on the work function of ZnO. It was found that increasing surface coverage of organic groups and decreasing surface defects lead to decrease of work functions, in excellent agreement with experimental results. First principles based calculations thus can greatly contribute to the investigating and designing of new electronic materials.
Contributing Partner: UNT Libraries
Indentation induced deformation in metallic materials.

Indentation induced deformation in metallic materials.

Date: December 2005
Creator: Vadlakonda, Suman
Description: Nanoindentation has brought in many features of research over the past decade. This novel technique is capable of producing insights into the small ranges of deformation. This special point has brought a lot of focus in understanding the deformation behavior under the indenter. Nickel, iron, tungsten and copper-niobium alloy system were considered for a surface deformation study. All the samples exhibited a spectrum of residual deformation. The change in behavior with indentation and the materials responses to deformation at low and high loads is addressed in this study. A study on indenter geometry, which has a huge influence on the contact area and subsequently the hardness and modulus value, has been attempted. Deformation mechanisms that govern the plastic flow in materials at low loads of indentation and their sensitivity to the rate of strain imparted has been studied. A transition to elastic, plastic kind of a tendency to an elasto-plastic tendency was seen with an increase in the strain rate. All samples exhibited the same kind of behavior and a special focus is drawn in comparing the FCC nickel with BCC tungsten and iron where the persistence of the elastic, plastic response was addressed. However there is no absolute reason ...
Contributing Partner: UNT Libraries
An Integrated Approach to Determine Phenomenological Equations in Metallic Systems

An Integrated Approach to Determine Phenomenological Equations in Metallic Systems

Date: December 2012
Creator: Ghamarian, Iman
Description: It is highly desirable to be able to make predictions of properties in metallic materials based upon the composition of the material and the microstructure. Unfortunately, the complexity of real, multi-component, multi-phase engineering alloys makes the provision of constituent-based (i.e., composition or microstructure) phenomenological equations extremely difficult. Due to these difficulties, qualitative predictions are frequently used to study the influence of microstructure or composition on the properties. Neural networks were used as a tool to get a quantitative model from a database. However, the developed model is not a phenomenological model. In this study, a new method based upon the integration of three separate modeling approaches, specifically artificial neural networks, genetic algorithms, and monte carlo was proposed. These three methods, when coupled in the manner described in this study, allows for the extraction of phenomenological equations with a concurrent analysis of uncertainty. This approach has been applied to a multi-component, multi-phase microstructure exhibiting phases with varying spatial and morphological distributions. Specifically, this approach has been applied to derive a phenomenological equation for the prediction of yield strength in a+b processed Ti-6-4. The equation is consistent with not only the current dataset but also, where available, the limited information regarding certain ...
Contributing Partner: UNT Libraries
Interspecimen Study of Bone to Relate Macromechanical, Nanomechanical and Compositional Changes Across the Femoral Cortex of Bone

Interspecimen Study of Bone to Relate Macromechanical, Nanomechanical and Compositional Changes Across the Femoral Cortex of Bone

Access: Use of this item is restricted to the UNT Community.
Date: May 2013
Creator: Nar, Mangesh
Description: Mechanics of bone is widely studied and researched, mainly for the study of fracture. This has been done mostly on a macro scale. In this work hierarchical nature of bone has been explored to investigate bone mechanics in more detail. Flexural test were done to classify the bones according to their strength and deflection. Raman spectroscopy analysis was done to map the mineralization, collagen crosslinking changes across the thickness of the bone. Nanoindentation was done to map indentation hardness and indentation modulus across femoral cortex of the bone. The results indicate that the composition of the bone changes across the thickness of the femoral cortex. The hypothesis is confirmed as increase in mineralization, carbonate to phosphate ratio and collagen crosslinking shows the effect as increased indentation hardness and modulus and decreased deflection.
Contributing Partner: UNT Libraries
Investigation of growth kinetics of self-assembling monolayers by means of contact angle, optical ellipsometry, angle-resolved XPS and IR spectroscopy.

Investigation of growth kinetics of self-assembling monolayers by means of contact angle, optical ellipsometry, angle-resolved XPS and IR spectroscopy.

Date: August 2004
Creator: Jakubowicz, Agnieszka
Description: Absorption of octadecanethiol and p-nitrobenzenethiol onto gold surfaces from ethanol solutions has been studied by means of contact angle, optical ellipsometry, angle-resolved XPS (ARXPS), and with grazing angle total reflection FTIR. Growth of the monolayers from dilute solutions has been monitored and Langmuir isotherm adsorption curves were fitted to experimental data. A saturated film is formed within approximately 5h after immersion in solutions of concentrations ranging from 0.0005mM to 0.01mM. We found, that the final density of monolayer depends on the concentration of the solution.
Contributing Partner: UNT Libraries
Laser Deposition, Heat-treatment, and Characterization of the Binary Ti-xmn System

Laser Deposition, Heat-treatment, and Characterization of the Binary Ti-xmn System

Date: August 2013
Creator: Avasarala, Chandana
Description: The present research seeks to characterization of an additively manufactured and heat-treated Ti-xMn gradient alloy, a binary system that has largely been unexplored. In order to rapidly assess this binary system, compositionally graded Ti-xMn (0<x<15 wt%) specimens were fabricated using the LENS (Laser Engineered Net Shaping) and were subsequently heat-treated and characterized using a wide range of techniques. Microstructural changes with respect to the change in thermal treatments, hardness and chemical composition were observed and will be presented. These include assessments of both continuous cooling, leading to observations of both equilibrium and metastable phases, including the titanium martensites, and to direct aging studies looking for composition regimes that produce highly refined alpha precipitates – a subject of great interest given recent understandings of non-classical nucleation and growth mechanisms. The samples were characterized using SEM, EDS, TEM, and XRD and the properties probed using a Vickers Microhardness tester.
Contributing Partner: UNT Libraries
Laser Modified Alumina: a Computational and Experimental Analysis

Laser Modified Alumina: a Computational and Experimental Analysis

Date: December 2012
Creator: Moncayo, Marco Antonio
Description: Laser surface modification involves rapid melting and solidification is an elegant technique used for locally tailoring the surface morphology of alumina in order to enhance its abrasive characteristics. COMSOL Multiphysics® based heat transfer modeling and experimental approaches were designed and used in this study for single and multiple laser tracks to achieve densely-packed multi-facet grains via temperature history, cooling rate, solidification, scanning electron micrographs, and wear rate. Multi-facet grains were produced at the center of laser track with primary dendrites extending toward the edge of single laser track. The multiple laser tracks study indicates the grain/dendrite size increases as the laser energy density increases resulting in multiplying the abrasive edges which in turn enhance the abrasive qualities.
Contributing Partner: UNT Libraries
Laser Surface Modification on Az31b Mg Alloy for Bio-wettability

Laser Surface Modification on Az31b Mg Alloy for Bio-wettability

Date: December 2013
Creator: Ho, YeeHsien
Description: Laser surface modification of AZ31B Magnesium alloy changes surface composition and roughness to provide improved surface bio-wettability. Laser processing resulted in phase transformation and grain refinement due to rapid quenching effect. Furthermore, instantaneous heating and vaporization resulted in removal of material, leading the textured surface generation. A study was conducted on a continuum-wave diode-pumped ytterbium laser to create multiple tracks for determining the resulting bio-wettability. Five different laser input powers were processed on Mg alloy, and then examined by XRD, SEM, optical profilometer, and contact angle measurement. A finite element based heat transfer model was developed using COMSOL multi-physics package to predict the temperature evolution during laser processing. The thermal histories predicted by the model are used to evaluate the cooling rates and solidification rate and the associated changes in the microstructure. The surface energy of laser surface modification samples can be calculated by measuring the contact angle with 3 different standard liquid (D.I water, Formamide, and 1-Bromonaphthalen). The bio-wettability of the laser surface modification samples can be conducted by simulated body fluid contact angle measurement. The results of SEM, 3D morphology, XRD, and contact angle measurement show that the grain size and roughness play role for wetting behavior of ...
Contributing Partner: UNT Libraries