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Carbon And Other Low-Z Materials Under Extreme Conditions, Jonathan T. Willman

USF Tampa Graduate Theses and Dissertations

This work is focused on understanding material's behavior and response to extreme conditions. Under extreme conditions, which is categorized as regions of high pressures and temperatures in (P-T) space, materials can undergo multiple types of phase transitions as well as exhibit substantial damage as well as other exotic behaviors. By studying matter at these extreme conditions, we can elucidate a broad range of fundamental physics including a material's energetic, mechanical, and electronic responses. This thesis describes work that makes contributions to the growing body of knowledge within these subsets of condensed matter physics. In the first thrust, crystal structure prediction …

Computational Studies Of Carbon Nanocluster Solidification, Chathuri C. Silva

Dissertations

A subset of micron-size meteoritic carbon particles formed in red giant atmospheres show a core-rim structure, likely condensed from a vapor phase into super-cooled carbon droplets that nucleated graphene sheets (~40Å) on randomly oriented 5-atom loops during solidification, followed by coating with a graphite rim. Similar particles form during slow cooling of carbon vapor in the lab.

Here we investigate the nucleation and growth of carbon rings and graphene sheets using density functional theory (DFT). Our objectives: (1). explore different computational techniques in DFT-VASP for various carbon structures and compare the results with literature, (2). investigate the nucleation and growth …

Fundamental Aspects Of The Interaction Between Light And Nanostructures, Stephen Keith Sanders

Physics & Astronomy ETDs

Recent breakthroughs in nanophotonics have brought new opportunities to control and manipulate light at the nanoscale. The optical properties of metallic nanostructures have attracted particular interest because of their plasmon resonances, which couple strongly with visible light, and generate large near-field enhancements in their vicinity. In the first part of this thesis, we investigate the fundamental limits of the local density of photonic states near nanostructures by analyzing a sum rule relating its spectral integral to the field induced by a static dipole. Next, we analyze how the design of metallic nanoantennas can benefit from incorporating active materials that display …

Fabrication And Characterization Of Photodetector Devices Based On Nanostructured Materials: Graphene And Colloidal Nanocrystals, Wafaa Gebril

Graduate Theses and Dissertations

Photodetectors are devices that capture light signals and convert them into electrical signals. High performance photodetectors are in demand in a variety of applications, such as optical communication, security, and environmental monitoring. Among many appealing nanomaterials for novel photodetection devices, graphene and semiconductor colloidal nanocrystals are promising candidates because of their desirable and unique properties compared to conventional materials.

Photodetector devices based on different types of nanostructured materials including graphene and colloidal nanocrystals were investigated. First, graphene layers were mechanically exfoliated and characterized for device fabrication. Self-powered few layers graphene phototransistors were studied. At zero drain voltage bias and room …

Strongly Correlated Phases In Quantum Hall Systems, Amartya Saha

Theses and Dissertations--Physics and Astronomy

Quantum Hall systems have a one-body energy spectrum consisting of dispersion-less Landau levels. Electron-electron interactions thus dominate in partially filled Landau levels, which exhibit a myriad of strongly correlated phases such as quantum hall ferromagnets and fractional quantum Hall phases. We study two examples of these phenomena.

In the first project, we explore the ground state of a system with an interface between two semi-infinite regions with fillings ν= 4 and ν= 3 respectively. The width of the interface can be controlled by varying the background potential, which provides an additional tuning parameter. For a certain range of …

Electronic Properties Of Flat And Curved Graphene Sheets, Deng Yanpei

Senior Projects Spring 2021

This paper explored the electronic properties of the graphene sheet and also developed basis for understanding the electronic properties of the curved graphene sheet. This paper began with setting up basic knowledge about solid-state physics including introducing band structure, band gap, crystal structure, and reviews for quantum mechanical operators. Then this paper described two potential models that are suitable for considering periodic potential: the weak potential and the tight-binding model. We discovered the tight-binding model is better for our graphene case and by applying this model we find the energies of the graphene sheet. Next, we constructed the 1D and …

Computational Studies Of Carbon Nanocluster Solidification, Chathuri Chandani Silva

Doctoral Dissertations

“A subset of micron-size meteoritic carbon particles formed in red giant atmospheres show a core-rim structure, likely condensed from a vapor phase into super-cooled carbon droplets that nucleated graphene sheets (~40Å) on randomly oriented 5-atom loops during solidification, followed by coating with a graphite rim. Similar particles form during slow cooling of carbon vapor in the lab.

Here we investigate the nucleation and growth of carbon rings and graphene sheets using density functional theory (DFT). Our objectives: (1). explore different computational techniques in DFT-VASP for various carbon structures and compare the results with literature, (2). investigate the nucleation and growth …

Semi-Empirical Modeling Of Liquid Carbon's Containerless Solidification, Philip C. Chrostoski

Doctoral Dissertations

“Elemental carbon has important structural diversity, ranging from nanotubes through graphite to diamond. Previous studies of micron-size core/rim carbon spheres extracted from primitive meteorites suggest they formed around such stars via the solidification of condensed carbon-vapor droplets, followed by gas-to-solid carbon coating to form the graphite rims. Similar core/rim particles result from the slow cooling of carbon vapor in the lab. The long-range carbon bond-order potential was used to computationally study liquid-like carbon in (1.8 g/cm³) periodic boundary (tiled-cube supercell) and containerless (isolated cluster) settings. Relaxations via conjugate-gradient and simulated-annealing nucleation and growth simulations using molecular dynamics were …

Experimental Investigations Of Contact Friction And Transport Properties Of Monolayer And Bilayer Graphene, Prakash Gajurel

Graduate Theses, Dissertations, and Problem Reports

Results obtained from experimental investigations of contact friction in monolayer and bilayers graphene and the related effects on their transport properties are presented here along with their discussion and interpretation. For this purpose, chemical vapor deposited (CVD) graphene samples on SiO₂/Si were prepared. The samples were characterized by atomic force microscopy (AFM), Raman and X-ray photoelectron spectroscopy (XPS). Summaries of the results are given below.

Defects-controlled friction in graphene is of technological importance but the underlying mechanism remains a subject of debate. The new results obtained from the analysis of lateral force microscopy images revealed that the contact …

Two-Dimensional Bose–Hubbard Model For Helium On Graphene, Jiangyong Yu

Graduate College Dissertations and Theses

An exciting development in the field of correlated systems is the possibilityof realizing two-dimensional (2D) phases of quantum matter. For a systems of bosons, an example of strong correlations manifesting themselves in a 2D environment is provided by helium adsorbed on graphene. We construct the effective Bose-Hubbard model for this system which involves hard-core bosons (U ≈ ∞) and repulsive nearest-neighbor (V > 0) interactions. In this work, we focus on the calculations of single particle properties of the model such as the hopping parameter t. This is accomplished via Wannier Theory and Band structure calculations, which proves to be reliable …