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Search Publications by: Angela R. Hight Walker (Fed)

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Displaying 76 - 100 of 195

Separation of Double-Wall Carbon Nanotubes by Electronic Type and Diameter

January 24, 2017
Author(s)
Jason K. Streit, Stephanie Lam, Yanmei Piao, Angela R. Hight Walker, Jeffrey A. Fagan, Ming Zheng
In this work, we introduce a new procedure for the efficient isolation and subsequent separation of double-wall carbon nanotubes (DWCNTs). A simplified rate zonal ultracentrifugation (RZU) process is first applied to obtain samples of highly enriched

The rheo-Raman microscope: Simultaneous chemical, conformational, mechanical, and microstructural measures of soft materials

October 4, 2016
Author(s)
Anthony P. Kotula, Matthew Meyer, Francesca De Vito, Jan Plog, Angela R. Hight Walker, Kalman D. Migler
We describe the design and demonstrate performance of an instrument capable of simultaneous Raman spectroscopy, rheology, and optical microscopy of materials. The instrument couples a Raman microscope with a rotational rheometer through an optically

Toward Clean Suspended CVD Graphene

August 26, 2016
Author(s)
Alexander Yulaev, Guangjun Cheng, Angela R. Hight Walker, Ivan Vlassiouk, Alline Myers, Marina S. Leite, Andrei Kolmakov
The application of suspended graphene as electron transparent supporting media in electron microscopy, vacuum electronics, and micromechanical devices requires the least destructive and maximally clean transfer from their original growth substrate to the

Charge Carrier Dynamics and Mobility Determined by Time-Resolved Terahertz Spectroscopy on Films of Nano-to-Micrometer-Sized Colloidal Tin(II) Monosulfide

August 1, 2016
Author(s)
Brian Alberding, Adam Biacchi, Angela R. Hight Walker, Edwin J. Heilweil
Tin(II) monosulfide (SnS) is a semiconductor material with an intermediate band gap, high absorption coefficient is the visible range, and consists of earth abundant, non-toxic elements. For these reasons, SnS has generated much interest for incorporation

Enhancing Single-Wall Carbon Nanotube Properties Through Controlled Endohedral Filling

May 10, 2016
Author(s)
Jochen I. Campo, Yanmei Piao, Stephanie Lam, Christopher Stafford, Jason K. Streit, Jeffrey R. Simpson, Angela R. Hight Walker, Jeffrey Fagan
Chemical control of the endohedral volume of single-wall carbon nanotubes (SWCNTs) via liquid-phase filling is demonstrated to be a facile strategy to controllably modify properties of the nanotubes in manners significant for processing and proposed

Intensity Ratio of Resonant Raman Modes for (n,m) Enriched Semiconducting Carbon Nanotubes

April 29, 2016
Author(s)
Yanmei Piao, Jeffrey R. Simpson, Jason K. Streit, Geyou Ao, Ming Zheng, Angela R. Hight Walker
Relative intensities of resonant Raman spectral features, specifically the radial breathing mode (RBM) and G modes, of eleven chirality-enriched single-wall carbon nanotube (SWCNT) species were established under second-order optical transition excitation

Field Effects of Current Crowding at Metal-MoS2 Contacts

March 10, 2016
Author(s)
Hui H. Yuan, Guangjun Cheng, Sheng Yu, Angela R. Hight Walker, Curt A. Richter, Qiliang Li
Gate assisted contact-end Kelvin test structures and gate assisted 4-probe structures have been designed and fabricated to measure the field effects of current crowding at the source/drain contacts of top-gate MoS2 field effect transistors. The transistors

Lightweight, flexible, high-performance carbon nanotube cables by scalable flow coating*

January 21, 2016
Author(s)
Nathan D. Orloff, Francesca Mirri, Aaron M. Forster, Rana NMN Ashkar, Robert Headrick, E. A. Bengio, Christian J. Long, April Choi, Yimin Luo, Angela R. Hight Walker, Paul Butler, Kalman D. Migler, Matteo Pasquali
Coaxial cables for data transmission are ubiquitously used in telecommunications, aerospace, automotive and robotics industries. Unfortunately, the metals used to make commercial cables are heavy and stiff. These undesirable traits are particularly

Fe-catalyzed etching of exfoliated graphite through carbon hydrogenation

January 8, 2016
Author(s)
Guangjun Cheng, Christina A. Hacker, Curt A. Richter, Angela R. Hight Walker
We present an investigation on the etching of graphite catalyzed by the particles produced by dewetting Fe thin films on graphite in forming gas. Raman mapping of the etched graphite shows the thickness variation in the etched channels and reveals that the

Broadband Optical Properties of Graphene by Spectroscopic Ellipsometry

December 11, 2015
Author(s)
Wei Li, Nhan Van Nguyen, Guangjun Cheng, Angela R. Hight Walker, David J. Gundlach, Yiran Liang, boyuan Tian, Xuelei Liang, Lian-Mao Peng
The broadband (0.7 eV to 9.0 eV) optical properties of chemical-vapor-deposition (CVD) grown graphene are determined by spectroscopic ellipsometry. The optical absorption follows the fine structure constant in the energy range from 1.0 eV to 2.0 eV, but

Detecting Carbon in Carbon: Application of Differential Charging to Obtain Information on the Chemical Identity and Spatial Location of Carbon Nanotube Aggregates in Composites by Imaging X-ray Photoelectron Spectroscopy

October 24, 2015
Author(s)
Justin M. Gorham, William A. Osborn, Jeremiah W. Woodcock, Keana C. Scott, John M. Heddleston, Angela R. Hight Walker, Jeffrey W. Gilman
The surface contributions and dispersion properties of multiwalled carbon nanotubes (MWCNT) within a composite are important measurements to perform on nano-enabled products in order to help answer environmental health and safety questions associated with

Mesomorphic Pathway in Early Stage Crystallization of Polyethylene

June 18, 2015
Author(s)
Kalman D. Migler, Angela R. Hight Walker, Anthony P. Kotula
The kinetic pathway by which a molten polymer transforms into a multi-length scale semi-crystalline structure upon cooling is an unsolved problem in polymer physics, yet it is critical to the processing, properties and ultimate performance of these

How Large Can We Go? Isolation of > 1 nm Diameter Single-Wall Carbon Nanotubes Species using Aqueous Two Phase Extraction

April 14, 2015
Author(s)
Jeffrey A. Fagan, Erik Haroz, Rachelle Ihly, Hui Gui, Jeffrey Blackburn, Jeffrey R. Simpson, Stephen K. Doorn, Stephanie Lam, Angela R. Hight Walker, Ming Zheng
We demonstrate the effective separation of near-monochiral single-wall carbon nanotube (SWCNT) species with diameters > 1 nm through multi-stage aqueous two phase extraction (ATPE), and report an empirical function for the surfactant concentrations at

Redox sorting of carbon nanotubes

March 17, 2015
Author(s)
Hui Gui, Jason K. Streit, Jeffrey Fagan, Angela R. Hight Walker, Chongwu Zhou, Ming Zheng
This work expands the redox chemistry of single-wall carbon nanotube (SWCNT) by investigating its role in a number of SWCNT sorting processes. Using a polyethylene glycol (PEG)/dextran (DX) aqueous two-phase system, we show that electron-transfer reaction

Influence of Metal?MoS2 Interface on MoS2 Transistor Performance: Comparison of Ag and Ti Contacts

December 16, 2014
Author(s)
Hui H. Yuan, Guangjun Cheng, Lin You, Haitao Li, Hao Zhu, Wei Li, Joseph J. Kopanski, Yaw S. Obeng, Angela R. Hight Walker, David J. Gundlach, Curt A. Richter, D. E. Ioannou, Qiliang Li
In this work, we present a study of enhancing MoS2 transistor performance by using proper metal contact. We found that the on-state current of MoS2 field-effect transistors with 30 nm Au/ 30 nm Ag contacts is enhanced more than 60 times and the

High-Speed Coherent Raman Fingerprint Imaging of Biological Tissues

July 20, 2014
Author(s)
Charles H. Camp, Young J. Lee, John M. Heddleston, Christopher M. Hartshorn, Angela R. Hight Walker, Jeremy N. Rich, Justin D. Lathia, Marcus T. Cicerone
We have developed a coherent Raman imaging platform using broadband coherent anti-Stokes Raman scattering (BCARS) that provides an unprecedented combination of speed, sensitivity, and spectral breadth. The system utilizes a unique configuration of laser

State of the Art Raman Techniques for Biological Applications

July 1, 2014
Author(s)
Angela R. Hight Walker, Alasdair Rae, Rainer Stosch, Petr Klapetek, Debdulal Roy
Raman spectroscopy is a powerful tool for the elucidation of qualitative and quantitative information from biological systems and has huge potential in areas such as biotechnologies, drug discovery, agro-chemical research and clinical diagnostics. This