Physics Commons^™

Enhanced Li Capacity In Functionalized Graphene: A First Principle Study With Van Der Waals Correction, Rajiv K. Chouhan, Pushpa Raghani

Pushpa Raghani

We have investigated the adsorption of Li on graphene oxide using density functional theory. We show a novel and simple approach to achieve a positive lithiation potential on epoxy and hydroxyl functionalized graphene, compared to the negative lithiation potential that has been found on prestine graphene. We included the van der Waals correction into the calculation so as to get a better picture of weak interactions. A positive lithiation potential suggests a favorable adsorption of Li on graphene oxide sheets that can lead to an increase in the specific capacity, which in turn can be used as an anode material …

Enhanced Li Capacity In Functionalized Graphene: A First Principle Study With Van Der Waals Correction, Rajiv K. Chouhan, Pushpa Raghani

Physics Faculty Publications and Presentations

We have investigated the adsorption of Li on graphene oxide using density functional theory. We show a novel and simple approach to achieve a positive lithiation potential on epoxy and hydroxyl functionalized graphene, compared to the negative lithiation potential that has been found on prestine graphene. We included the van der Waals correction into the calculation so as to get a better picture of weak interactions. A positive lithiation potential suggests a favorable adsorption of Li on graphene oxide sheets that can lead to an increase in the specific capacity, which in turn can be used as an anode material …

Tunneling Experiments With Dirac Electrons In Graphene Heterojunctions, Shivani Rajput

Theses and Dissertations

This dissertation presents results of scanning tunneling microscopy/spectroscopy experiments performed on graphene, a two-dimensional membrane of carbon atoms arranged in a honeycomb lattice, where charge carriers behave like massless fermions described by the Dirac equation. Our findings demonstrate that interface engineering is a viable route to control and further enhance the electronic properties of graphene.

In the first experiment, by transferring chemical vapor deposited (CVD) graphene onto substrates of opposite polarization - H-terminated Si-face and C-faces of hexagonal silicon carbide (SiC), we show that the type of charge carrier in graphene can be controlled by substrate polarization. Furthermore, we find …

Measuring Charge Carrier Mobility In Graphene, Christina A. Harmon

Senior Theses

This research reports measurements of electron mobility in Graphene Field Effect Transistors (GFET), gated with liquid. Mobility is a quantity describing how easily charge carriers move through a material. GFET biosensors have the greatest sensitivity when the mobility is high; therefore, increasing mobility should improve sensitivity of these and similar devices. An optimal method was established for preparing samples and taking measurements of a liquid-gate device. Sheet conductivity was measured using van der Pauw geometry and carrier density was determined from measurements of the liquid-gate capacitance. It is shown that mobility improves after the graphene surface is cleaned by an …

Modelling Transient Terahertz Magneto-Spectroscopy Measurements Of P-Type Cvd Graphene Leading To A Negative Photoconductivity., Rhyan Foo Kune

Macalester Journal of Physics and Astronomy

Ultrafast Terahertz (THz) Magneto-Spectroscopy (UTMS) measurements were performed on p-type CVD graphene sample to investigate the intrinsic carrier dynamics of the material. We investigated static and time-resolved THz transmission measurements, in which the sample was photo-excited by a near infrared (NIR) pump pulse, in order to study its behavior in a magnetic field. In these measurements the free carriers were probed to independently measure the carrier density and scattering rate in this film. We observed, in our graphene sample, an increase in transmission related to a negative photoconductivity (decrease in conductivity after photoexcitation) consistent with previous research. This decrease is …

Mid-Ir Excitation Of Graphene, Andrew R. Banman, James Heyman

Macalester Journal of Physics and Astronomy

In this research we investigate how the conductivity of graphene changes in response to mid-infrared photoexcitation. Our p-type sample was formed through chemical vapor deposition. Pump/probe methodology produced the time-resolved Terahertz transmission, from which the photoconductivity was calculated. We probed the sample with energies above and below the Fermi energy, which was determined by Fourier transform infrared spectroscopy. Our results support a model in which heating of the electron gas, leading to high carrier scattering rates, is responsible for a decrease in conductivity. We observe this negative photoconductivity at all pump energies, allowing us to rule out the possibility of …

Optical Characterization Of Carbon Nanotube Forests, Brian D. Wood

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Carbon nanotube forests are vertically grown tubular formations of graphene. Due to their inherent microstructure and geometry, they are ideal light absorbers over a broad spectrum, making this material an excellent absorber in applications such as radiometry, optical calibration, and stray light suppression. Samples were made with several growth conditions and substrates to provide forests of different morphologies. Optical data of these samples were gathered by taking spectroscopic reflectance and transmittance measurements in the mid-infrared spectral range. Results were correlated to the various forest morphologies. From this, the conditions necessary to maximize the absorption of the forests were found and …

Mirror Buckling Transitions In Freestanding Graphene Membranes Induced Through Scanning Tunneling Microscopy, James Kevin Schoelz

Graduate Theses and Dissertations

Graphene has the ability to provide for a technological revolution. First isolated and characterized in 2004, this material shows promise in the field of flexible electronics. The electronic properties of graphene can be tuned by controlling the shape of the membrane. Of particular interest in this endeavor are the thermal ripples in graphene membranes. Years of theoretical work by such luminaries as Lev Landau, Rudolf Peierls, David Mermin and Herbert Wagner have established that 2D crystals should not be thermodynamically stable. Experimental research on thin films has supported this finding. Yet graphene exists, and freestanding graphene films have been grown …

So(8) Fermion Dynamical Symmetry In Graphene, Matthew Murphy

Chancellor’s Honors Program Projects

No abstract provided.

The Science Of Two Dimensional Materials (Powerpoint), Jun Yan

Nanotechnology Teacher Summer Institutes

Graphene is a single atomic sheet of graphite.

Exercise: how much graphene do we need to cover the surface of the empire state building?

Electronic Transport Properties Of Carbon Nanotubes: The Impact Of Atomic Charged Impurities, Ryuichi Tsuchikawa

Electronic Theses and Dissertations

Even changing one atom in nanoscale materials is expected to alter their properties due to their small physical sizes. Such sensitivity can be utilized to modify materials' properties from bottom up and is essential for the utility of nanoscale materials. As such, the impact of extrinsic atomic adsorbates was measured on pristine graphene and a network of carbon nanotubes using atomic hydrogen, cesium atoms, and dye molecules. In order to further quantify such an atomic influence, the resistance induced by a single potassium atom on metallic and semiconducting carbon nanotubes was measured for the first time. Carbon nanotubes are sensitive …

Using Graphene To Control Magnetic Anisotropy And Interaction Between Supported Clusters, Sanjubala Sahoo, M Fhokrul Islam, Shiv N. Khanna

Physics Publications

Stabilization of magnetic order in clusters/nanoparticles at elevated temperatures is a fundamentally challenging problem. The magnetic anisotropy energy (MAE) that prevents the thermal fluctuations of the magnetization direction can be around 1–10 K in free transition metal clusters of around a dozen atoms. Here we demonstrate that a graphene support can lead to an order of magnitude enhancement in the anisotropy of supported species. Our studies show that the MAE of supported Co5 and Co13 clusters on graphene increase by factors of 2.6 and 25, respectively. The enhancement is linked to the splitting of selected electronic orbitals that leads to …

Nanoelectronic Devices Using Carbon Nanotubes And Graphene Electrodes: Fabrication And Electronic Transport Investigations, Narae Kang

Electronic Theses and Dissertations

Fabrication of high-performance electronic devices using the novel semiconductors is essential for developing future electronics which can be applicable in large-area, flexible and transparent displays, sensors and solar cells. One of the major bottlenecks in the fabrication of high-performance devices is a large interfacial barrier formation at metal/semiconductor interface originated from Schottky barrier and interfacial dipole barrier which causes inefficient charge injection at the interface. Therefore, having a favorable contact at electrode/semiconductor is highly desirable for high-performance devices fabrication. In this dissertation, the fabrication of nanoelectronic devices and investigation of their transport properties using carbon nanotubes (CNTs) and graphene as …

Nano And Nanostructured Materials For Optical Applications, Panit Chantharasupawong

Electronic Theses and Dissertations

Nano and nanostructured materials offer unique physical and chemical properties that differ considerably from their bulk counterparts. For decades, due to their fascinating properties, they have been extensively explored and found to be beneficial in numerous applications. These materials are key components in many cutting-edge optic and photonic technologies, including photovoltaics, waveguides and sensors. In this dissertation, the uses of nano and nanostructured materials for optical applications are investigated in the context of optical limiting, three dimensional displays, and optical sensing. Nanomaterials with nonlinear optical responses are promising candidates for self-activating optical limiters. In the first part of this study, …

Synthesis, Integration, And Physical Characterization Of Graphene And Carbon Nanotubes, David P. Hunley

Theses and Dissertations--Physics and Astronomy

Graphene and carbon nanotubes are among the hottest topics in physics today. Both materials exhibit numerous remarkable mechanical, electrical, optical, and thermal properties that make them promising materials for use in a large number of diverse applications, especially in the field of nanotechnology. One of the ultimate goals driving the fields of nanoscience and nanotechnology has been the attainment of atomically precise construction of intricate integrated systems consisting of materials with diverse behavior. Specifically, it is desirable to have high performance conductors, semiconductors, and insulators integrated into complex atomically precise arrangements. This dissertation represents the culmination of work that has …