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

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Displaying 76 - 100 of 173

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

Tearing and scrolling of transferred graphene

April 29, 2014
Author(s)
Guangjun Cheng, Brent A. Sperling, James E. Maslar, Curt A. Richter, Angela R. Hight Walker
We present an investigation on tearing and scrolling of the transferred graphene on a Si/SiO2 substrate. Graphene grown by chemical vapor deposition (CVD) is transferred onto a Si/SiO2 substrate using a wet polymer-mediated process. Upon the removal of

Highly reproducible and reliable metal/graphene contact by UV-Ozone treatment

March 17, 2014
Author(s)
Wei Li, Christina A. Hacker, Guangjun Cheng, Angela R. Hight Walker, Curt A. Richter, David J. Gundlach, Yiran Liang, boyuan Tian, Xuelei Liang, Lianmao Peng
Resist residue from the device fabrication process is a significant source of contamination at the metal/graphene contact interface. Ultraviolet Ozone (UVO) treatment is proven here, by X-ray photoelectron spectroscopy (XPS) and Raman measurement, to be an

Isolation of Specific Small Diameter Single-Wall Carbon Nanotube Species via Aqueous Two-Phase Extraction

January 21, 2014
Author(s)
Jeffrey A. Fagan, Constantine Y. Khripin, Carlos A. Silvera Batista, Jeffrey R. Simpson, Angela R. Hight Walker, Ming Zheng
Aqueous two-phase extraction (ATPE) is demonstrated to enable isolation of multiple semiconducting and metallic single-wall carbon nanotube species from a small diameter synthetic mixture. Separation by ATPE is rapid and robust, with remarkable tunability

Thermal Conductivity of Monolayer MoS2 Obtained from Temperature-Dependent Raman Spectroscopy

December 30, 2013
Author(s)
Rusen Yan, Jeffrey R. Simpson, Simone Bertolazzi, Jacopo Brivio, Michael Watson, Xufei Wu, Andras Kis, Tengfei Luo, Angela R. Hight Walker, Huili G. Xing
Atomically thin molybdenum disulphide (MoS2) is emerging as a potential alternative to graphene due to presence of bandgap, which is particularly advantageous to optoelectronic applications. The temperature-dependent Raman spectra of exfoliated monolayer

Analyzing Surfactant Structures on Length and Chirality Resolved (6,5) Single-Wall Carbon Nanotubes by Analytical Ultracentrifugation

March 26, 2013
Author(s)
Jeffrey A. Fagan, Ming Zheng, Jeffrey R. Simpson, Vinayak Rastogi, Constantine Y. Khripin, Carlos A. Silvera Batista, Angela R. Hight Walker
The structure and density of the bound interfacial surfactant layer and associated hydration shell were investigated using analytical ultracentrifugation for length and chirality purified (6,5) single-wall carbon nanotubes (SWCNTs) in three different bile

Determination of graphene work function and graphene-insulator-semiconductor band alignment by internal photoemission spectroscopy

July 11, 2012
Author(s)
Rusen Yan, Qin Zhang, Wei Li, Irene G. Calizo, Tian T. Shen, Curt A. Richter, Angela R. Hight Walker, Xuelei X. Liang, David J. Gundlach, Nhan Van Nguyen, Huili G. Xing, Alan Seabaugh
We determined the band alignment of a graphene-oxide-silicon structure using internal photoemission spectroscopy. From the flatband voltage and Dirac voltage we infer a 4.3 10e11 cm-2 negative extrinsic charge present on the graphene surface. Also, we

Characteristics of Graphene for Quantized Hall Effect Measurements

June 1, 2012
Author(s)
Randolph E. Elmquist, Mariano A. Real, Irene G. Calizo, Brian G. Bush, Tian T. Shen, Nikolai N. Klimov, David B. Newell, Angela R. Hight Walker, Randall M. Feenstra
This paper describes concepts and measurement techniques necessary for characterization of graphene in the development of graphene-based quantized Hall effect (QHE) devices and resistance standards. We briefly contrast the properties of graphene produced

Relationship between Length and Surface-Enhanced Raman Spectroscopy signal Strength in Metal Nanoparticle Chains: Idea Models versus Nanofabrication

January 18, 2012
Author(s)
Angela R. Hight Walker, K. Stec, Shunpig Zhang, Hongxing Xu, Rene Lopez
We have employed capillary force deposition on ion beam patterned substrates to fabricate chains of 60nm gold nanospheres ranging in length from 1 to 9 nanoparticles. Measurements of the surface-averaged SERS enhancement factor strength for these chains