Search Results

Unexpected Structures for Intercalation of Sodium in Epitaxial Graphene-SiC Interfaces

Description: In this paper, the authors show using scanning tunneling microscopy, spectroscopy, and ab initio calculations that several intercalation structures exist for Na in epitaxial graphene on SiC(0001). Intercalation takes place at room temperature and Na electron-dopes the graphene. It intercalates in-between single-layer graphene and the carbon-rich interfacial layer. It also penetrates beneath the interfacial layer and decouples it to form a second graphene layer. This decoupling is accelerated by annealing and is verified by direct Na deposition onto the interface layer. The authors' observations show that intercalation in graphene is fundamentally different than in graphite and is a versatile means of electronic control.
Date: February 2012
Creator: Sandin, Andreas; Jayasekera, Thushari; Rowe, J. E.; Kim, Ki Wook; Buongiorno Nardelli, Marco & Dougherty, Daniel B.
Item Type: Paper
Partner: UNT College of Arts and Sciences

Phonon engineering in nanostructures: Controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions

Description: Article discussing phonon engineering in nanostructures and controlling interfacial thermal resistance in multilayer-graphene/dielectric heterojunctions.
Date: September 13, 2012
Creator: Mao, R.; Kong, Byoung Don; Kim, Ki Wook; Jayasekera, Thushari; Calzolari, Arrigo & Buongiorno Nardelli, Marco
Item Type: Article
Partner: UNT College of Arts and Sciences

Brittle and Ductile Behavior in Carbon Nanotubes

Description: Article discussing research on the response of carbon nanotubes to a tensile load.
Date: November 23, 1998
Creator: Buongiorno Nardelli, Marco; Yakobson, Boris I. & Bernholc, Jerry
Item Type: Article
Partner: UNT College of Arts and Sciences

On the mechanism for plasma hydrogenation of graphene

Description: This article discusses the mechanism for plasma hydrogenation of graphene.
Date: December 6, 2010
Creator: Jones, Jason D.; Hoffmann, William D.; Jesseph, Aaron V.; Morris, Christopher; Verbeck, Guido F. & Pérez, José M.
Item Type: Article
Partner: UNT College of Arts and Sciences

Biocompatible Graphene-based Growth of Cancer Cells: A Work in Progress

Description: Poster presentation for the 2012 University Scholars Day at the University of North Texas. This poster discusses research on the biocompatible graphene-based growth of cancer cells. Graphene is made of a single layer of carbon atoms. Recently is has been used to successfully differentiate stem cells in neural cells.
Date: April 19, 2012
Creator: Parks, Melissa & Verrill, Diane
Item Type: Poster
Partner: UNT Honors College

Enhancements of Mechanical, Thermal Stability, and Tribological Properties by Addition of Functionalized Reduced Graphene Oxide in Epoxy

Description: The effects of octadecylamine-functionalized reduced graphene oxide (FRGO) on the frictional and wear properties of diglycidylether of bisphenol-A (DGEBA) epoxy are studied using a pin-on-disk tribometer. It was observed that the addition of FRGO significantly improves the tribological, mechanical, and thermal properties of epoxy matrix. Graphene oxide (GO) was functionalized with octadecylamine (ODA), and then reduction of oxygen-containing functional groups was carried out using hydrazine monohydrate. The Raman and x-ray photoelectron spectroscopy studies confirm significant reduction in oxygen-containing functional groups and formation of ODA functionalized reduced GO. The nanocomposites are prepared by adding 0.1, 0.2, 0.5 and 1.0 wt % of FRGO to the epoxy. The addition of FRGO increases by more than an order of magnitude the sliding distance during which the dynamic friction is ≤ 0.1. After this distance, the friction sharply increases to the range of 0.4 - 0.5. We explain the increase in sliding distance during which the friction is low by formation of a transfer film from the nanocomposite to the counterface. The wear rates in the low and high friction regimes are approximately 1.5 x 10-4 mm3/N·m and 5.5 x 10-4 mm3/N·m, respectively. The nanocomposites exhibit a 74 % increase in Young’s modulus with 0.5 wt. % of FRGO, and an increase in glass transition and thermal degradation temperatures.
Date: August 2014
Creator: Shah, Rakesh K.
Partner: UNT Libraries

Direct Atomic Level Controlled Growth and Characterization of h-BN and Graphene Heterostructures on Magnetic Substrates for Spintronic Applications

Description: Epitaxial multilayer h-BN(0001) heterostructures and graphene/h-BN heterostructures have many potential applications in spintronics. The use of h-BN and graphene require atomically precise control and azimuthal alignment of the individual layers in the structure. These in turn require fabrication of devices by direct scalable methods rather than physical transfer of BN and graphene flakes, and such scalable methods are also critical for industrially compatible development of 2D devices. The growth of h-BN(0001) multilayers on Co and Ni, and graphene/h-BN(0001) heterostructures on Co have been studied which meet these criteria. Atomic Layer Epitaxy (ALE) of BN was carried out resulting in the formation of macroscopically continuous h-BN(0001) multilayers using BCl3 and NH3 as precursors. X-ray photoemission spectra (XPS) show that the films are stoichiometric with an average film thickness linearly proportional to the number of BCl3/NH3 cycles. Molecular beam epitaxy (MBE) of C yielded few layer graphene in azimuthal registry with BN/Co(0001) substrate. Low energy electron diffraction (LEED) measurements indicate azimuthally oriented growth of both BN and graphene layers in registry with the substrate lattice. Photoemission data indicate B:N atomic ratios of 1:1. Direct growth temperatures of 600 K for BN and 800 to 900 K for graphene MBE indicate multiple integration schemes for applications in spintronics.
Date: August 2016
Creator: Beatty, John D.
Partner: UNT Libraries

The Effects of Residual Gases on the Field Emission Properties of ZnO, GaN, ZnS Nanostructures, and the Effects of Light on the Resistivity of Graphene

Description: In this dissertation, I present that at a vacuum of 3×10-7 Torr, residual O2, CO2, H2 and Ar exposure do not significantly degrade the field emission (FE) properties of ZnO nanorods, but N2 exposure significantly does. I propose that this could be due to the dissociation of N2 into atomic nitrogen species and the reaction of such species with ZnO. I also present the effects of O2, CO2, H2O, N2, H2, and Ar residual gas exposure on the FE properties of GaN and ZnS nanostructure. A brief review of growth of ZnO, GaN and ZnS is provided. In addition, Cs deposition on GaN nanostructures at ultra-high vacuum results in 30% decrease in turn-on voltage and 60% in work function. The improvement in FE properties could be due to a Cs-induced space-charge layer at the surface that reduces the barrier for FE and lowers the work function. I describe a new phenomenon, in which the resistivity of CVD-grown graphene increases to a higher saturated value under light exposure, and depends on the wavelength of the light—the shorter the wavelength, the higher the resistivity. First-principle calculations and theoretical analysis based on density functional theory show that (1) a water molecule close to a graphene defect is easier to be split than that of the case of no defect existing and (2) there are a series of meta-stable partially disassociated states for an interfacial water molecule. Calculated disassociation energies are from 2.5 eV to 4.6 eV, that match the experimental observation range of light wavelength from visible to 254 nm UV light under which the resistivity of CVD-grown graphene is increased.
Date: May 2014
Creator: Mo, Yudong
Partner: UNT Libraries

Rationally designed graphene-nanotube 3D architectures with a seamless nodal junction for efficient energy conversion and storage

Description: This article discusses the development of a strategy of creating 3D graphene-carbon nanotube hollow fibers with radially aligned CNTs (RACNTs) seamless sheathed by a cylindrical graphene layer through a one-step chemical vapor deposition using an anodized aluminum wire template.
Date: September 4, 2015
Creator: Xue, Yuhua; Ding, Yong; Niu, Jianbing; Xia, Zhenhai; Roy, Ajit; Chen, Hao et al.
Item Type: Article
Partner: UNT College of Engineering

Effects of light on the resistivity of chemical vapor deposited graphene films

Description: This article reports that the resistance of a chemical vapor deposition (CVD) grown graphene film transferred onto an SiO₂ substrate increases to higher saturation values upon exposure to light of decreasing wavelength from the visible to ultraviolet.
Date: October 24, 2016
Creator: Mo, Yudong; Pérez, José M.; Ye, Zhou; Zhao, Lei; Yang, Shizhong; Tan, Liuxi et al.
Item Type: Article
Partner: UNT College of Arts and Sciences