Engineering Commons^™

Exploring The Electrical Properties Of Twisted Bilayer Graphene, William Shannon

Senior Theses

Two-dimensional materials exhibit properties unlike anything else seen in conventional substances. Electrons in these materials are confined to move only in the plane. In order to explore the effects of these materials, we have built apparatus and refined procedures with which to create two-dimensional structures. Two-dimensional devices have been made using exfoliated graphene and placed on gold contacts. Their topography has been observed using Atomic Force Microscopy (AFM) confirming samples with monolayer, bilayer, and twisted bilayer structure. Relative work functions of each have been measured using Kelvin Probe Force Microscopy (KPFM) showing that twisted bilayer graphene has a surface potential …

Measuring The Double Layer Capacitance Of Electrolyte Solutions Using A Graphene Field Effect Transistor, Agatha Ulibarri

Senior Theses

When operating graphene field effect transistors (GFETs) in fluid, a double layer capacitance (C_dl) is formed at the surface. In the literature, the C_dl is estimated using values obtained using metal electrode experiments. Due to the distinctive electronic and surface properties of graphene, there is reason to believe these estimates are inadequate. This work seeks to directly characterize the double layer capacitance of a GFET. A unique method for determining the C_dl has been implemented, and data has been obtained for three electrolytes and one ionic fluid. The results yield dramatically lower C_dl values than …

Fabrication And Characterization Of Graphene Based 2d Materials For Supercapacitors, Anishkumar Manoharan

Graduate Theses and Dissertations

Supercapacitors have attracted a lot attention due to their efficient energy storage. In comparison to batteries, supercapacitors have high capacitance, energy, and power densities per unit mass than conventional capacitors. Carbon based materials are most promising in supercapacitor application due to their outstanding physical and electrochemical behavior. In this work, a facile method to synthesize a nanocomposite electrode consisting of annealed carbon from carbon ink and MoS2 was demonstrated. Effects of various aqueous and solid electrolytes were studied. It was found that the nanocomposite electrode with 10% MoS2 and 1M Na2SO4 as the aqueous electrolyte tested using the three electrode …

Thermoelectric Transport And Energy Conversion Using Novel 2d Materials, Luke J. Wirth

Browse all Theses and Dissertations

Nanomaterials hold great promise for applications in thermal management and thermoelectric power generation. Defects in these are important as they are generally inevitably introduced during fabrication or intentionally engineered to control the properties of the nanomaterials. Here, we investigate how phonon-contributed thermal conductance in narrow graphene, boron nitride (BN), and silicene nanoribbons (NRs), responds to the presence of a vacancy defect and the corresponding geometric distortion, from first principles using the non-equilibrium Green's function method. Analyses are made of the geometries, phonon conductance coefficients, and local densities of states (LDOS) of pristine and defected nanoribbons. It is found that hydrogen …

Synthesis Of Graphene And Its Applications For Dye-Sensitized Solar Cells, Hui Wang

Dissertations, Master's Theses and Master's Reports - Open

Graphene, which is a two-dimensional carbon material, exhibits unique properties that promise its potential applications in photovoltaic devices. Dye-sensitized solar cell (DSSC) is a representative of the third generation photovoltaic devices. Therefore, it is important to synthesize graphene with special structures, which possess excellent properties for dye-sensitized solar cells.

This dissertation research was focused on (1) the effect of oxygen content on the structure of graphite oxide, (2) the stability of graphene oxide solution, (3) the application of graphene precipitate from graphene oxide solution as counter electrode for DSSCs, (4) the development of a novel synthesis method for the three-dimensional …

Synthesis And Characterization Of Graphene Oxide/Sulfur Nanocomposite For Lithium-Ion Batteries, Aaron Joseph Blake

Browse all Theses and Dissertations

The growing need for clean and efficient energy storage systems has recently peaked due to concerns of climate change and increased global energy consumption. However, efficiently integrating renewable resources such as solar and wind energy into society will require a complex electrical energy storage (EES) system capable of storing and expending significant amounts of energy. A battery based on the lithium/sulfur couple can yield a theoretical specific energy of 2600Wh/kg, which is about five times higher than that offered by present Li-ion batteries, and hence, is a promising and attractive technology. Despite recent developments in addressing various issues inherent to …