Physics Commons^™

Momentum Space Algorithm For Electronic Structure Of Double-Incommensurate Trilayer Graphene, Kenneth Silver Beard

LSU Doctoral Dissertations

Numerical algorithms for computing the electronic structure of incommensurate 2D-materials using ab initio models are critical for predicting material properties and guiding experiments. For bilayers, momentum space and continuum models have been introduced to approximate observables of ab initio tight-binding models using a momentum description, despite the lack of periodicity in the tight-binding model required for Bloch theory. A similar structure has been introduced for double-incommensurate trilayers using a continuum model, where the three lattices are mutually incommensurate. However, this description leads to a four-dimensional lattice space, and numerical convergence of the density of states has been observed to be …

Plasma-Enhanced Carbon Nanomaterial Synthesis: A Pathway To Reducing Greenhouse Gasses And Carbon-Based Waste., Zane Ronau

Electronic Theses and Dissertations

This research leveraged incorporation of capacitively coupled radio frequency plasma into chemical vapor deposition (CVD) for a reduction in the temperature requirements [a reduction of energy barrier] needed for the conversion of methane (CH₄), carbon dioxide (CO₂), and various carbon-based-waste to produce value-added carbon nanomaterials. An array of catalysts and catalyst supports were employed to optimize the synthesis of graphitic carbon under various gas environments, temperatures and pressures. The nanomaterials synthesized after fine tuning the growth parameters included graphene, carbon nanotubes (CNT), carbon microtubes and carbon nanocages with a variety of properties. Raman Spectroscopy was used …

Effect Of Space Radiation On The Mechanical Properties Of High-Strength Polyethylene Nanocomposite Films, Seunghyun Moon, Achal Duhoon, Zhongtian Gu, Jr Dennison, Tengfei Luo

Journal Articles

This study experimentally investigates the effects of prolonged radiation exposure on mechanical properties of high-strength, highly crystalline polyethylene (PE)/thermally reduced graphene oxide (TrGO) nanocomposite films for space applications. Prior to irradiation, PE/TrGO films were found to have tensile strengths up to ~4 GPa, more than 40 times that of conventional space-deployed membrane films (e.g., those used in solar sails) and over 59× the specific tensile strength. The PE/TrGO films were subjected to three radiation conditions to simulate space environmental conditions: ⁹⁰Sr beta radiation (0.2 to 2.5 MeV), 80 keV electron beam irradiation, and 4.9 eV ultraviolet (254 nm) exposure. …

Spectrum Analysis Of Thermally Driven Curvature Inversion In Strained Graphene Ripples For Energy Conversion Applications Via Molecular Dynamics, James M. Mangum, Md R. Kabir, Tamzeed B. Amin, Syed M. Rahman, Ashaduzzaman, Paul M. Thibado

Physics Faculty Publications and Presentations

The extraordinary mechanical flexibility, high electrical conductivity, and nanoscale instability of freestanding graphene make it an excellent candidate for vibration energy harvesting. When freestanding graphene is stretched taut and subject to external forces, it will vibrate like a drum head. Its vibrations occur at a fundamental frequency along with higher-order harmonics. Alternatively, when freestanding graphene is compressed, it will arch slightly out of the plane or buckle under the load. Remaining flat under compression would be energetically too costly compared to simple bond rotations. Buckling up or down, also known as ripple formation, naturally creates a bistable situation. When the …

Microwave Frequency Probes Of Graphene, Xinyi Du

Arts & Sciences Graduate Student Theses and Dissertations

We investigate high-frequency microwave spectroscopy as a probe of the electronic structure of graphene, focusing on compressibility, magnetic response, and the potential for detection applications. Graphene is a single layer of carbon atoms arranged in a hexagonal lattice, exhibiting unique electronic properties due to its band structure and reduced dimensionality. While traditional compressibility measurements rely on low-frequency capacitance techniques, this thesis explores a high-frequency approach using superconducting resonators to probe the compressibility of graphene in the GHz regime. Originally conceived as a means to examine the diamagnetic response, the method faces fundamental limitations due to resistive losses, revealing key challenges …

Quantum Hall Phases In Monolayer Graphene, Jincheng An

Theses and Dissertations--Physics and Astronomy

In the presence of a perpendicular magnetic field, monolayer graphene at and near charge neutrality forms a quantum Hall ferromagnet—a correlated electronic state where the interplay of interactions, spin, and valley degrees of freedom leads to spontaneous symmetry breaking. While the dominant Coulomb interaction has $SU(4)$ symmetry, the ground state is ultimately determined by subdominant terms: residual lattice-scale anisotropic interactions, Zeeman, and sublattice couplings. Relaxing the ultra-short-range limit of anisotropic interactions unveils diverse symmetry-breaking phases in both integer and fractional quantum Hall regimes. Haldane pseudopotentials, which quantify interactions between particle pairs with fixed relative angular momentum, provide a readily parameterizable …

Graphene-Based Antennas Utilizing Polyvinylidene Fluoride (Pvdf) Substrates For Attenuation, Josef Frankhouse

Mechanical Engineering Undergraduate Honors Theses

In this study, a Terahertz (THz) band antenna which can regulate its own resonant frequency without the requirement of manual adjustment is simulated. A polyvinylidene fluoride (PVDF) substrate is applied onto a rectangular graphene patch antenna. With a voltage potential applied onto the PVDF, the patch antenna can attenuate its frequency by physically changing the shape of the antenna, and in turn its resonant frequency. These antennas are within a 0.1 THz band between 1.32 THz to 1.22 THz measured from a radial bend of a flat surface to r = 75 , fitting into a return loss (S_{11 …}

Design And Fabrication Of Graphene Solar Cells For Low-Power Energy Harvesting Systems, Tamzeed Bani Amin

Graduate Theses and Dissertations

This study presents the design and fabrication of graphene-based Schottky junction solar cells integrated into a 3-volt power system for low-power applications. Utilizing standard semiconductor processing methods, including selective oxide removal, metal contact deposition, and large-area graphene transfer, we fabricated solar cells from a silicon wafer coated with a thermal oxide layer. Each individual solar cell generated up to 270 µA of short-circuit current and an open-circuit voltage of 420 mV under illumination. We connected multiple solar cells in series to produce a total output of 3.3 volts, which is sufficient to recharge a 3-volt battery. The system, comprising these …

Emergent Phenomena In Ferroelectric-Dielectric And Ferroelectric-Graphene Heterostructures, Tianlin Li

Dissertations and Doctoral Documents, University of Nebraska-Lincoln, 2023–

This dissertation explores the emergent phenomena in epitaxial ferroelectric oxide-based heterostructures, including the negative capacitance (NC) effect in ferroelectric-dielectric systems, ferroelectric gate imposed mobility limit in graphene field-effect transistors, and ferroelectric domain-induced graphene-superlattices.

We carry out a phenomenological study of the NC effect in PbZr_0.2Ti_0.8O₃/SrTiO₃ capacitors. The Landau free-energy profile predicts a critical thickness ratio for the ferroelectric-dielectric phase transition, consistent with the observed abrupt change in remnant polarization. A static NC state is observed in the low thickness ratio region, which is compromised by the emergence of multidomain in the moderate ratio …

Density Functional Theory Calculations On Electronic And Optical Properties Of Mos2/Metal Heterojunction, Mos2/Graphene/Metal Vertical Heterostructure Interfaces And Sulfur Vacancies On Mos2/Au, Shishir Timilsena

Theses and Dissertations

In this study, we conducted a comprehensive investigation on computational simulations and analyses of heterostructures formed by two-dimensional (2D) molybdenum disulfide (MoS2) and graphene (Gr) on various metal coated substrates, including gold (Au), copper (Cu), nickel (Ni), and platinum (Pt). The frequency-dependent dielectric function (ɛ(ω)), refractive index (n), and reflectivity (R) are determined using light polarization parallel and perpendicular to the c axis of the 2D layers. Our findings reveal that MoS2/Au, MoS2/Cu, and MoS2/Pt heterostructures exhibit a direct bandgap at the K-point of the Brillouin zone, whereas their corresponding MoS2/MoS2/Metal structures present an indirect bandgap. The reduced interlayer spacing …

Rela&Onship Between The Height Of Graphene And Its Adhesion Value, Tyler Larson

Senior Theses

Two-dimensional materials, such as graphene, have remarkable proper&es. As one of the thinnest, strongest, and most conduc&ve materials known to humanity, graphene holds promise for revolu&onizing numerous technological applica&ons. These applica&ons all require different numbers of layers of graphene. However, with graphene being so thin it is difficult to quickly determine how many layers there are. By using an adhesion value and a height value of graphene one may be able to iden&fy the number of layers more accurately.

Optical Thickness Determination Of Hexagonal Boron Nitride By Color, Jacob Slifka

Senior Theses

No abstract provided.

Infrared Magneto-Spectroscopy Of Correlated Electron Systems In Graphene, Yashika Kapoor

Arts & Sciences Graduate Student Theses and Dissertations

Van der Waals (vdW) heterostructures represent a novel class of artificial materials created by layering atomically thin planar crystals and offer a promising platform for band structure engineering. Here, we focus on a vdW heterostructure of monolayer graphene (G) coupled to a hexagonal boron nitride (h-BN). We utilize cyclotron resonance (CR) spectroscopy as a primary investigative tool for probing the interacting Dirac fermions in graphene. This work presents a system capable of conducting broadband far- to mid-infrared CR spectroscopy in high magnetic fields and ultra-low temperatures. Our study investigates the influence of the h-BN substrate on the properties of graphene …

The Analysis Of Mechanical Exfoliation Of Graphene For Various Fabrication And Automation Techniques, Lance Yarbrough

Physics Undergraduate Honors Theses

Mechanical Exfoliation

Encapsulated 2d Materials And The Potential For 1d Electrical Contacts, Sarah Wittenburg

Physics Undergraduate Honors Theses

The utilization of two-dimensional materials and heterostructures, particularly graphene and hexagonal boron nitride, have garnered significant attention in the realm of nanoelectronics due to their unique properties and versatile functionalities. This study focuses on the synthesis and fabrication processes of monolayer graphene encapsulated between layers of hBN, aiming to explore the potential of these heterostructures for various electronic applications. The encapsulation of graphene within hBN layers not only enhances device performance but also shields graphene from environmental contaminants, ensuring long-term stability. Experimental techniques, including mechanical exfoliation and stamp-assisted transfer, are employed to construct three-layer stacks comprising hBN-graphene-hBN. The fabrication process …

Magnetic Properties Of Zgnrs With Nitrogen And Fluorine Adsorbates, A Computational Study, Justin Petit

Electronic Theses and Dissertations

Imposing dimensional restrictions on graphene sheets and adding impurities can give rise to carbon nanostructures with magnetic properties. In this work, zigzag graphene nanoribbons, zGNRs, with nitrogen and fluorine adatoms are investigated for magnetic properties of interest for spin devices. Geometry optimizations were done determining which position along a zGNR electrode that N and F would favorably attach to. Edge positions were determined as the most stable attachment site. M-cell zGNR electrodes (M = 1-3) edge-functionalized by N and F adatoms were investigated with respect to their band structures and spin densities in antiferromagnetic and ferromagnetic, AFM and FM, configurations. …

The Analysis Of Mechanical Exfoliation Of Graphene For Various Fabrication And Automation Techniques, Lance Yarbrough

Mechanical Engineering Undergraduate Honors Theses

Mechanical Exfoliation of Graphene is an often-overlooked portion of the fabrication of quantum devices, and to create more devices quickly, optimizing this process to generate better flakes is critical. In addition, it would be valuable to simulate test pulls quickly, to gain insight on flake quality of various materials and exfoliation conditions. Physical pulls of graphene at various temperatures, pull forces, and pull repetitions were analyzed and compared to the results of ANSYS simulations, solved for similar results. Using ANSYS’ ability to predict trends in exfoliations, flake thickness and coverage using stress and deflection analyses were investigated. Generally, both strongly …

Etching Of Silicon Wafer In Preparation Of Graphene Transfer, Floyd T. Lancaster Iii

Graduate Theses and Dissertations

Following the research done on graphene looking at its unique properties it has been found that graphene can be used as a varying capacitor. What has been observed is that graphene acts almost like a torrential ocean constantly fluctuating. What we use is a silicon wafer with multiple etched layers to create a stable platform on which to capture this energy. In this paper we will discuss the general setup and step-by-step procedures required to create a functioning variable capacitor out of graphene, gold, and Silicon dioxide (SiO2) substrate. Electron Beam Lithography (EBL) is used to create the initial design …

Circuitry And Semiconductor Studies For Making A Graphene Energy Harvesting Device, Ferdinand Harerimana

Graduate Theses and Dissertations

Freestanding graphene has constantly moving ripples. Due to its extreme flexibility, graphene responds to ambient vibrations and changes its curvature from concave to convex and vice versa. During a ripple inversion 10,000 atoms move together, suggesting the presence of kinetic energy which can be harvested. In this study we present circuitry and semiconductor studies for harvesting energy from graphene vibrations. The goal of the study is to develop a graphene energy harvesting chip which can serve as a battery replacement in low power electronics. In the first study we determined the best circuit for harvesting vibrational low power. To do …

Analysis And Application Of Finite Element And High-Order Finite Difference Methods For Maxwell’S Equations In Complex Media, Li Zhu

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Perfectly Matched Layer (PML) technique is an effective tool introduced by B´erenger [13] to reduce the unbounded wave propagation problem to a bounded domain problem. This dissertation focuses on two different PML models and their applications to wave propagation problems with Maxwell’s equation in complex media. We investigate these models using two popular numerical methods: the Finite Difference Method (FDM) in Chapters 2 and 3, and the Finite Element Method (FEM) in Chapters 4 and 5.In Chapter 2, we focus on analyzing the stability of a PML developed by B’ecache et al. [10] for simulating wave propagation in the …

Analog Cosmology And Superfluidity In Atomic Gases And Electronic Materials, Anshuman Bhardwaj

LSU Doctoral Dissertations

We present a study of analog cosmological models in Bose-Einstein condensates (BEC) and in graphene, and superfluidity in a box-shaped traps. We start by examining the dynamics of a Bose-Einstein condensate (BEC) trapped inside an expanding toroid that can realize an analog inflationary universe. The expanding condensate forces phonons to undergo redshift and damping due to quantum pressure, owing to the thinness of the ring. We predict that such expanding BECs can exhibit spontaneous phonon creation from the vacuum state and show how it would manifest in the atom density and density correlations and discuss connections with the inflationary theory. …

A Study Of Single Molecule Detection With Graphene Hall Bars, Kenneth Stephen Stephenson

Theses and Dissertations

In 2007, detection of individual molecules with a solid-state gas sensor was reported for first time by Schedin et al. where they used micromechanically-cleaved graphene for their sensing material, which exhibits isotropic and homogeneous conduction [1]. However, despite the novelty and popularity of their work, it has never been repeated. Further, we found their associated calculations to be self-inconsistent by a factor of 103 . So, hoping to account for and resolve this discrepancy, we outline the plan we had to reproduce their experiment. We also justify any substantial modifications, particularly our choice to use epitaxial graphene instead. Then, we …

Low Energy Photon Detection, Tianyi Guo

Graduate Thesis and Dissertation 2023-2024

Detecting long wave infrared (LWIR) light at room temperature has posed a persistent challenge due to the low energy of photons. The pursuit of an affordable, high-performance LWIR camera capable of room temperature detection has spanned several decades. In the realm of contemporary LWIR detectors, they can be broadly classified into two categories: cooled and uncooled detectors. Cooled detectors, such as MCT detectors, excel in terms of high detectivity and fast response times. However, their reliance on cryogenic cooling significantly escalates their cost and restricts their practical applications. In contrast, uncooled detectors, exemplified by microbolometers, are capable of functioning at …

Towards The Electronic Response Of Carbon-Based Van Der Waals Heterostructures In A Diamond Anvil Cell, George Thomas Foskaris

UNLV Theses, Dissertations, Professional Papers, and Capstones

The nanoscale regime of materials has been at the forefront of research and interest in condensed matter physics for many years. In a merger of the fields of two-dimensional (2D) materials and high pressure physics, we present an investigation of the electronic response of carbon-based, van der Waals (vdW) heterostructures in a diamond anvil cell (DAC). Combining these fields presents us with the ability to study the characteristics of such systems both optically, and through electrical transport. Properties such as conductance, band structure, and layer number are considered. The samples in this study are assembled using exfoliation and stacking techniques …

Plasmon Damping Rates In Coulomb-Coupled 2d Layers In A Heterostructure, Dipendra Dahal, Godfrey Gumbs, Andrii Iurov, Chin-Sen Ting

Publications and Research

The Coulomb excitations of charge density oscillation are calculated for a double-layer heterostructure. Specifically, we consider two-dimensional (2D) layers of silicene and graphene on a substrate. From the obtained surface response function, we calculated the plasmon dispersion relations, which demonstrate how the Coulomb interaction renormalizes the plasmon frequencies. Most importantly, we have conducted a thorough investigation of how the decay rates of the plasmons in these heterostructures are affected by the Coulomb coupling between different types of two- dimensional materials whose separations could be varied. A novel effect of nullification of the silicene band gap is noticed when graphene is …

Custom Calibration And Correction Of Photoemission Electron Microscope Images Using Graphene, Henry Bell

Macalester Journal of Physics and Astronomy

The Photoemission Electron Microscope (PEEM) is a full-field electron microscope that utilizes the photoelectric effect to image a surface. Due to a spatial resolution on the order of 10 nanometers and its ability to image both the morphology of a surface and its band structure, it is a useful tool for understanding the properties of materials for use in electronic devices. To correct for random sample misalignment and the experimental frame of reference in the spectroscopy mode of the PEEM, the 3D dataset must be rotated in both the momentum and energy coordinates which requires pixel calibration and energy alignment. …

Design, Fabrication, And Characterization Of An Array Of Graphene Based Variable Capacitors, Millicent Nkirote Gikunda

Graduate Theses and Dissertations

Since it was first isolated and characterized in 2004, graphene has shown the potential for a technological revolution. This is due to its amazing physical properties such as high electrical conductivity, high thermal conductivity, and extreme flexibility. Freestanding graphene membranes naturally possesses an intrinsic rippled structure, and these ripples are in constant random motion even room temperatures. Occasionally, the ripples undergo spontaneous buckling (change of curvature from concave to convex and vice versa) and the potential energy associated with this is a double well potential. This movement of graphene is a potential source of vibrational energy.

In this dissertation, we …

Ab Initio Studies Of Structure And Properties Of Group-Iv Monochalcogenide Monolayers, Shiva Prasad Poudel

Graduate Theses and Dissertations

The goal of this dissertation is to study the structure of ferroelectric group-IV monochalcogenide monolayers (MMLs) and their material properties. This work also established a new buckled honeycomb phase of these monolayers. Chapter 1 serves as an introduction where the motivation for these studies is established. In chapter 2, I used eight different exchange-correlation functionals (XC) to study the structure of these 2D ferroelectrics and found that their properties are independent of the choice of XC functionals. These findings reveal that the ground-state ferroelectric unit cell can be described by only five independent parameters, whereas their paraelectric (square or rectangular) …

Strain‑Induced Quantum Hall Phenomena Of Excitons In Graphene, Oleg L. Berman, Roman Ya. Kezerashvili, Yurii E. Lozovik, Klaus G. Ziegler

Publications and Research

We study direct and indirect pseudomagnetoexcitons, formed by an electron and a hole in the layers of gapped graphene under strain‑induced gauge pseudomagnetic field. Since the train‑induced pseudomagnetic field acts on electrons and holes the same way, it occurs that the properties of single pseudomagnetoexcitons, their collective effects and phase diagram are cardinally different from those of magnetoexcitons in a real magnetic field. We have derived wave functions and energy spectrum of direct in a monolayer and indirect pseudomagnetoexcitons in a double layer of gapped graphene. The quantum Hall effect for direct and indirect excitons was predicted in the monolayers …

Theoretical Investigation On Optical Properties Of 2d Materials And Mechanical Properties Of Polymer Composites At Molecular Level, Geeta Sachdeva

Dissertations, Master's Theses and Master's Reports

The field of two-dimensional (2D) layered materials provides a new platform for studying diverse physical phenomena that are scientifically interesting and relevant for technological applications. Theoretical predictions from atomically resolved computational simulations of 2D materials play a pivotal role in designing and advancing these developments. The focus of this thesis is 2D materials especially graphene and BN studied using density functional theory (DFT) and molecular dynamics (MD) simulations. In the first half of the thesis, the electronic structure and optical properties are discussed for graphene, antimonene, and borophene. It is found that the absorbance in (atomically flat) multilayer antimonene (group …