Materials Science and Engineering Commons^™

Electronically Enhanced Surface Diffusion During Ge Growth On Si(100), Ali Orguz Er, Hani E. Elsayed-Ali

Physics Faculty Publications

The effect of nanosecond pulsed laser excitation on surface diffusion during the growth of Ge on Si(100) at 250 °C was studied. In situ reflection high-energy electron diffraction was used to measure the surface diffusion coefficient while ex situ atomic force microscopy was used to probe the structure and morphology of the grown quantum dots. The results show that laser excitation of the substrate increases the surface diffusion during the growth of Ge on Si(100), changes the growth morphology, improves the crystalline structure of the grown quantum dots, and decreases their size distribution. A purely electronic mechanism of enhanced surface …

Stress Measurement And Development Of Zirconium Diboride-Silicon Carbide Ceramics, Jeremy Lee Watts

Doctoral Dissertations

"Research presented in this dissertation focused on the production of ZrB₂-SiC composites and their characterization; in particular their mechanical properties and thermally generated residual stresses. Thermally generated stresses were measured using Raman spectroscopy as well as both neutron and x-ray diffraction. For 70 vol% ZrB₂ - 30 vol% SiC composites neutron diffraction revealed that the SiC phase was under ~880 MPa compressive stress and the ZrB₂ phase was under ~450 MPa tension at room temperature. It was also discovered that stresses began to accumulate at ~1400 ⁰C upon cooling from the processing temperature (1900 ⁰C -2000 ⁰C). Raman spectroscopy and …

Two-Point Bend Studies Of Glass Fibers, Zhongzhi Tang

Doctoral Dissertations

"The principal objective of this research is to advance our understanding of how glass breaks. Glass, a material well known for its brittleness, has been used widely but within a frustrating limit of its strength. Generally, strength is not considered as an intrinsic property of glass, due to the difficulty of avoiding the presence of flaws on the sample surface. The fiber drawing system and two-point bending (TPB) equipment developed at Missouri S&T allow the fabrication of pristine glass fibers and failure strain measurements while minimizing the effects of strength limiting critical flaws. Several conditions affect the failure behavior of …

Alloy Dissolution In Argon Stirred Steel, Darryl S. Webber

Doctoral Dissertations

"Alloying is required for the production of all steel products from small castings to large beams. Addition of large quantities of bulk alloys can result in alloy segregation and inconsistent alloy recovery. The objective of this research was to better understand alloy dissolution in liquid steel especially as it relates to Missouri S&Ts' patented continuous steelmaking process. A 45-kilogram capacity ladle with a single porous plug was used to evaluate the effect of four experimental factors on alloy dissolution: alloy species, alloy size or form, argon flow rate, and furnace tap temperature. Four alloys were tested experimentally including Class I …

Additivity Of Strengthening Mechanisms In Ultrafine Grained Aluminum Alloy, Nilesh Kumar

Doctoral Dissertations

"Friction stir processing (FSP) has been used in the present work to obtain ultrafine grained (UFG) microstructure in a twin-roll cast (TRC) Al-Mg-Sc alloy. An attempt has been made to establish a correlation between processing, microstructure, and properties (mechanical) in UFG regime for this alloy system.

The effect of initial microstructural conditions and processing parameters (tool rotation rate) were shown to have a profound impact on the development of UFG microstructure. FSP led to a microstructure consisting of grains with an average grain size as small as 390 nm, having high angle grain boundaries and a completely random texture. The …

Processing And Characterization Of Boron Carbide-Hafnium Diboride Ceramics, Harlan J. Brown-Shaklee

Doctoral Dissertations

"Hafnium diboride based ceramics are promising candidate materials for advanced aerospace and nuclear reactor components. The effectiveness of boron carbide and carbon as HfB₂ sintering additives was systematically evaluated. In the first stage of the research, boron carbide and carbon additives were found to improve the densification behavior of milled HfB₂ powder in part by removing oxides at the HfB₂ surface during processing. Boron carbide additives reduced the hot pressing temperature of HfB₂ by 150⁰C compared to carbon, which reduced the hot pressing temperature by ~50⁰C. Reduction of oxide impurities alone could not explain the difference in sintering enhancement, however, …

Diamond Based-Materials: Synthesis, Characterization And Applications, Qiang Hu

USF Tampa Graduate Theses and Dissertations

The studies covered in this dissertation concentrate on the various forms of diamond films synthesized by chemical vapor deposition (CVD) method, including microwave CVD and hot filament CVD. According to crystallinity and grain size, a variety of diamond forms primarily including microcrystalline (most commonly referred to as polycrystalline) and nanocrystalline diamond films, diamond-like carbon (DLC) films were successfully synthesized. The as-grown diamond films were optimized by changing deposition pressure, volume of reactant gas hydrogen (H2) and carrier gas argon (Ar) in order to get high-quality diamond films with a smooth surface, low roughness, preferred growth orientation and high sp3 bond …

Oxygen Diffusion Characterization Of Frp Composites Used In Concrete Repair And Rehabilitation, Chandra K. Khoe

USF Tampa Graduate Theses and Dissertations

Many independent studies have conclusively demonstrated that fiber reinforced polymers (FRP) slow down chloride-induced corrosion of steel in concrete. The mechanism for this slow down is not well understood but it has been hypothesized that FRP serves as a barrier to the ingress of chloride, moisture, and oxygen that sustain electrochemical corrosion of steel.

This dissertation presents results from an experimental study that determined the oxygen permeation rates of materials used in infrastructure repair. In the study, the oxygen permeation constants for epoxy, carbon and glass fiber laminates, concrete, epoxy-concrete and FRP-concrete systems were determined and a method developed to …

Fabrication And Characterization Of Electrospun Cactus Mucilage Nanofibers, Yanay Pais

USF Tampa Graduate Theses and Dissertations

This work seeks to fabricate, optimize, and characterize nanofibers of cactus Opuntia ficus-indica mucilage and Poly (vinyl alcohol) (PVA) by electrospinning. Mucilage is a neutral mixture of sugars produced by cactus and PVA is a non-toxic, water-soluble, synthetic polymer, which is widely used as a co-spinning agent for polymers. Mucilage was extracted from the cactus pad and prepared for electrospinning by mixing with acetic acid. Two types of PVA were used differentiating in high and low molecular weights. Concentrations of PVA were varied to find an adequate threshold for fiber formation. Changing the ratio of PVA to cactus mucilage produced …

Stress Corrosion Cracking Evaluation Of Candidate High Strength Stainless Steels For Prestressed Concrete, Joseph Rogelio Fernandez

USF Tampa Graduate Theses and Dissertations

Prestressed concrete piles are commonly used to support over-water highway bridges in marine environments. The reinforcing steel within will ultimately be degraded via corrosion damage due to the penetration of chloride ions from sea water. The service life of these structures is, in part, dictated by the time required to diffuse chloride ions through the concrete cover and subsequently corrode the steel. Therefore, by slowing the rate of diffusion or increasing the chloride threshold of the steel (or both) an increased service life can be expected. This thesis focuses on the latter whereby stainless steel reinforcing alternatives were investigated to …

Interface Engineered Diamond Coatings For Dry Machining Applications, Humberto Arturo Gomez Vega

USF Tampa Graduate Theses and Dissertations

Several studies have been propose to improve the adhesion of diamond films on cemented carbide tool materials, however a systematic study in identifying the role of the factors that affect the final diamond adhesion and the resulting machining performance of the tool under real manufacturing conditions is still unexplored. CVD diamond film's extraordinary qualities bring little benefit if the film fails to adhere sufficiently to the substrate. Inadequate adhesion undermines tool performance and longevity, causing unpredictable behavior under load and possibly leading to unexpected failure of the tool in the production line. This dissertation investigates the effects of different surface …

Novel Magnetic Materials For Sensing And Cooling Applications, Anurag Chaturvedi

USF Tampa Graduate Theses and Dissertations

The overall goals of the present PhD research are to explore the giant magnetoimpedance (GMI) and giant magnetocaloric (GMC) effects in functional magnetic materials and provide guidance on the optimization of the material properties for use in advanced magnetic sensor and refrigeration applications.

GMI has attracted growing interest due to its promising applications in high-performance magnetic sensors. Research in this field is focused on the development of new materials with properties appropriate for practical GMI sensor applications. In this project, we have successfully set up a new magneto-impedance measurement system in the Functional Materials Laboratory at USF. We have established, …

Growth And Characterization Of Nanoscale Thin Films, Erik Thomas Wolter

Honors Program Theses

Thin manganese films were grown by thermal evaporation in high vacuum. The growth rate was varied to determine how the growth rate affects the continuity of ultra-thin films. The resistance was measured with the two-point method in situ and the data was recorded digitally. The resistance was converted to resistivity and this was plotted against thickness. It was found that resistivity decreases exponentially as the film begins to form in islands. The film reaches a critical thickness as the islands coalesce and the data can then be fitted with Fuchs’ equation. The resistivity continues to decrease but the minimum resistivity …