Physics Commons^™

Atomic-Level Mechanisms Of Fast Relaxation In Metallic Glasses, Leo W. Zella

Doctoral Dissertations

Glasses are ubiquitous in daily life and have unique properties which are a consequence of the underlying disordered structure. By understanding the fundamental processes that govern these properties, we can modify glasses for desired applications. Key to understanding the structure-dynamics relationship in glasses is the variety of relaxation processes that exist below the glass transition temperature. Though these relaxations are well characterized with macroscopic experimental techniques, the microscopic nature of these relaxations is difficult to elucidate with experimental tools due to the requirements of timescale and spatial resolution. There remain many questions regarding the microscopic nature of relaxation in glass …

Mechanical Behavior Of Metallic Core-Shell Nanoparticles Under Compressive Loading, Phillip Tomich

Graduate Research Theses & Dissertations

Core/shell metallic nanoparticles have been shown to be a promising material type for additive manufacturing in the aerospace and automotive fields. Within additive manufacturing they will be used to accurately make an array of nanoparticles within the grains of metal matrix composites. This in turn will help to strengthen the material while remaining ductility and light weight. In this study, copper/aluminum core/shell nanoparticles are compressed under [100], [110], [111], and [112] directions to showcase their anisotropic material properties. Models of their individual counterparts were also investigated. There are no previous works showing the deformation mechanisms of copper/aluminum core/shell nanoparticles. Molecular …

Multi-Scale Computational Modeling Of Metal/Ceramic Interfaces, Abu Shama Mohammad Miraz

Master's Theses

Multi-scale atomistic calculations were carried out to understand the interfacial features that dictate the mechanical integrity of the metal/ceramic nanolaminates. As such, first principles density functional theory (DFT) calculations were performed to understand the electronic and atomistic factors governing adhesion and resistance to shear for simple metal/ceramic interfaces, whereas molecular dynamics (MD) simulations were performed to observe the impact of interfacial structures, such as misfit dislocation network geometries and orientation relationships, on interfacial mechanical properties.

For the DFT investigation, we choose metals with different crystal structures, namely - Cu (fcc), Cr (bcc) and Ti (hcp) along with a variety of …

Multi-Scale Computational Modeling Of Metal/Ceramic Interfaces, Abu Shama Mohammad Miraz

Doctoral Dissertations

Multi-scale atomistic calculations were carried out to understand the interfacial features that dictate the mechanical integrity of the metal/ceramic nanolaminates. As such, first principles density functional theory (DFT) calculations were performed to understand the electronic and atomistic factors governing adhesion and resistance to shear for simple metal/ceramic interfaces, whereas molecular dynamics (MD) simulations were performed to observe the impact of interfacial structures, such as misfit dislocation network geometries and orientation relationships, on interfacial mechanical properties.

For the DFT investigation, we choose metals with different crystal structures, namely - Cu (fcc), Cr (bcc) and Ti (hcp) along with a variety of …

Mechanical Behavior Of Cyclo-18 On Nickel And Copper Substrates, Reagan Michael Kraft

Mechanical Engineering Undergraduate Honors Theses

Carbyne, an -hybridized allotrope of carbon, has been the subject of many studies recently due to its incredible mechanical properties and small size. More recently, another -hybridized allotrope known as cyclo-18, has gained interest. In this study, computational molecular dynamics will be used to determine the mechanical properties of cyclo-18. Peeling and shearing tests of the molecule will be conducted on nickel and copper, which are respectively active and less-active transition metals. Additionally, a carbyne chain of equal length will undergo the same tests on the copper substrate to compare the mechanical properties of the two. The results conclude that …

Building Predictive Chemistry Models, Christopher Browne, Nicolas Onofrio, Alejandro Strachan

The Summer Undergraduate Research Fellowship (SURF) Symposium

Density Functional Theory (DFT) simulations allow for sophisticated modeling of chemical interactions, but the extreme computational cost makes it inviable for large scale applications. Molecular dynamics models, specifically ReaxFF, can model much larger simulations with greater speed, but with lesser accuracy. The accuracy of ReaxFF can be improved by comparing predictions of both methods and tuning ReaxFF’s parameters. Molecular capabilities of ReaxFF were gauged by simulating copper complexes in water over a 200 ps range, and comparing energy predictions against ReaxFF. To gauge solid state capabilities, volumetric strain was applied to simulated copper bulk and the strain response functions used …

Non-Equilibrium Melting And Sublimation Of Graphene Simulated With Two Interatomic Potentials, Brad Steele

USF Tampa Graduate Theses and Dissertations

The mechanisms of the sublimation of graphene at zero pressure and the condensation of carbon vapor is investigated by molecular dynamics (MD) simulations. The interatomic interactions are described by the Reactive Empirical Bond Order potential (REBO). It is found that graphene sublimates at a temperature of 5,200 K. At the onset of sublimation, defects that contain several pentagons and heptagons are formed, that are shown to evolve from double vacancies and stone wales defects. These defects consisting of pentagons and heptagons act as nucleation sites for the gaseous phase. The influence of the interatomic interactions on the sublimation process are …

Development Of Interatomic Potentials For Large Scale Molecular Dynamics Simulations Of Carbon Materials Under Extreme Conditions, Romain Perriot

USF Tampa Graduate Theses and Dissertations

The goal of this PhD research project is to devise a robust interatomic potential for large scale molecular dynamics simulations of carbon materials under extreme conditions. This screened-environment dependent reactive empirical bond order potential (SED-REBO) is specifically designed to describe carbon materials under extreme compressive or tensile stresses. Based on the original REBO potential by Brenner and co workers, SED-REBO includes reparametrized pairwise interaction terms and a new screening term, which serves the role of a variable cutoff. The SED-REBO potential overcomes the deficiencies found with the most commonly used interatomic potentials for carbon: the appearance of artificial forces due …

Experimental And Theoretical Analysis Of Strain Engineered Aluminium Nitride On Silicon For High Quality Aluminium(X)Indium(Y)Gallium(1-X-Y)Nitride Epitaxy, Mihir Hemant Tungare

Legacy Theses & Dissertations (2009 - 2024)

III-Nitrides on Si are of great technological importance due to the availability of large area, epi ready Si substrates and the ability to heterointegrate with mature silicon micro and nanoelectronics. The major roadblock with realizing this is the large difference in thermal expansion coefficients and lattice constants between the two material systems. A novel technique developed in our research lab shows the potential of simultaneous and substantial reduction in dislocation and crack density in GaN on Si (111). Research undertaken in the current doctoral dissertation, validates the superior GaN quality on Si obtained using our technique and determines the factors …