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Search Publications by: Angela R. Hight Walker ()

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Displaying 101 - 125 of 173

Towards clean and crackless transfer of graphene

January 2, 2012
Author(s)
Xuelei X. Liang, Brent A. Sperling, Irene G. Calizo, Guangjun Cheng, Christina Hacker, Qin Zhang, Yaw S. Obeng, Kai Yan, Hailin Peng, Qiliang Li, Xiaoxiao Zhu, Hui Yuan, Angela R. Hight Walker, Zhongfan Liu, Lianmao Peng, Curt A. Richter
We present the results of a thorough study of wet chemical methods for transferring chemical vapor deposition grown graphene from the metal growth substrate to a device compatible substrate. Based on these results, we have developed a "modified RCA clean"

A Highly Practical Route for Large-Area, Single Layer Graphene from Liquid Carbon Sources such as Benzene and Methanol

October 28, 2011
Author(s)
Gadipelli Srinivas, Irene G. Calizo, Jamie Ford, Guangjun Cheng, Angela R. Hight Walker, Taner N. Yildirim
Through a detailed systematic study, we determined the parameters critical for high-quality, single-layer graphene formation and developed a straightforward synthesis that requires no explosive hydrogen or methane gas flow. The synthesis is further

Separation of Empty and Water-Filled Single-Wall Carbon Nanotubes

April 11, 2011
Author(s)
Jeffrey A. Fagan, Jeffrey R. Simpson, JiYeon Huh, Jeffrey Blackburn, Larsen A. Brian, Josh M. Holt, Angela R. Hight Walker
The separation of empty and water-filled laser ablation and electric arc synthesized nanotubes is reported. Centrifugation of these large-diameter nanotubes dispersed with sodium deoxycholate using specific conditions produces isolated bands of empty and

Evolution of Microscopic Localization in Graphene in a Magnetic Field: From Scattering Resonances to Quantum Dots.

January 9, 2011
Author(s)
Suyong S. Jung, Gregory M. Rutter, Nikolai Klimov, David B. Newell, Irene G. Calizo, Angela R. Hight Walker, Nikolai Zhitenev, Joseph A. Stroscio
Graphene is a unique material displaying high-mobility transport in monolayer-thin films. However, its properties are strongly dependent on interactions with substrates, local charges and environment. Scanned probe microscopies can be used to locally probe

Carbon Nanotubes: Measuring Dispersion and Length

August 26, 2010
Author(s)
Jeffrey A. Fagan, Barry J. Bauer, Erik K. Hobbie, Matthew Becker, Angela R. Hight Walker, Jeffrey R. Simpson, Jae H. Chun, Jan Obrzut, Vardhan Bajpai, Frederick R. Phelan Jr., Daneesh O. Simien, JiYeon Huh, Kalman D. Migler
Advanced technological uses of single-wall carbon nanotubes (SWCNTs) rely on the production of single length and chirality populations that are currently only available through liquid phase post processing. The foundation of all of these processing steps

Separation and Characterization of Double Wall Carbon Nanotube Sub-Populations

July 8, 2010
Author(s)
JiYeon Huh, Angela R. Hight Walker, Hyun W. Ro, Jan Obrzut, Jeffrey Fagan
We present the separation of surfactant encapsulated double wall carbon nanotubes (DWCNTs) synthesized by the high pressure carbon monoxide decomposition (HiPco) process by length and electronic characteristics using density gradient ultracentrifugation

Sample Preparation Protocols for Realization of Reproducible Characterization of Single-walled Carbon Nanotubes

December 1, 2009
Author(s)
Angela R. Hight Walker, Jeffrey A. Fagan, Stephanie A. Hooker, Michael T. Postek, Stephen A. Wise, Andras Vladar, Rolf L. Zeisler
Harmonized sample pre-treatment is an integral first step in ensuring metrological quality of measurements as regards repeatability, inter-laboratory reproducibility and commutability. The development of standard preparation methods for SWCNT samples is

Multimodal, Nanoscale, Hyperspectral Imaging Demonstrated on Heterostructures of Quantum Dots and DNA-Wrapped Single-Wall Carbon Nanotubes

October 21, 2009
Author(s)
Hyeong G. Kang, Matthew L. Clarke, Jianyong Tang, John T. Woodward IV, Shin G. Chou, Zhenping Zhou, Angela R. Hight Walker, Tinh Nguyen, Jeeseong Hwang
A multimodality imaging technique integrating atomic force, polarized Raman, and fluorescence lifetime microscopy and a 2D autocorrelation image analysis is applied to study the properties of a mesoscopic heterostucture of nanoscale materials. This

Probing the Growth and Aging of Colloidal Cobalt Nanoparticles

June 11, 2009
Author(s)
Guangjun Cheng, Cindi L. Dennis, Robert D. Shull, Angela R. Hight Walker
We have combined transmission electron microscopy (TEM) and magnetic measurements to characterize the growth of colloidal cobalt (Co) nanoparticles during synthesis and their subsequent stability in air. During the growth, TEM measurements have shown the

Dipolar Chains formed by synthesized cobalt nanocubes

May 11, 2009
Author(s)
Guangjun Cheng, Robert D. Shull, Angela R. Hight Walker
Cobalt nanocubes with an average edge length of 50 nm and the epsilon crystalline structure were synthesized via thermo-decomposition in 1,2-dichlorobenzene at 120 oC in the presence of the surfactants. These nanocubes form dipolar chains upon drying in

Centrifugal Length Separation of Carbon Nanotubes

October 1, 2008
Author(s)
Jeffrey A. Fagan, Matthew Becker, Jae H. Chun, Barry J. Bauer, Jeffrey R. Simpson, Angela R. Hight Walker, Erik K. Hobbie
Separation of single wall carbon nanotubes (SWCNTs) by length via centrifugation in a high density medium, and the characterization of both the separated fractions and the centrifugation process are presented. Significant quantities of the separated SWCNTs

Surface-Enhanced Raman Spectroscopy via Gold Nanostars

September 28, 2008
Author(s)
Emren Nalbant-Esenturk, Angela R. Hight Walker
Anisotropic metallic nanoparticles have unique optical properties, which lend them to applications such as Surface Enhanced Raman Spectroscopy (SERS). Branched and star-shaped gold nanoparticles have been prepared in aqueous phase by seed-mediated growth

Influence of the Colloidal Environment on the Magnetic Behavior of Cobalt Nanoparticles

November 6, 2007
Author(s)
Guangjun Cheng, Cindi L. Dennis, Robert D. Shull, Angela R. Hight Walker
The magnetic properties of 10 nm cobalt (Co) nanoparticles in 1,2-dicholorbenenze (DCB) are investigated via a series of magnetization (M) vs. temperature (T) measurements. A rapid rise in magnetization around 250 K during warming and a sudden drop at 240

Synthesis and Characterization of Cobalt/Gold Bimetallic Nanoparticles

April 1, 2007
Author(s)
Guangjun Cheng, Angela R. Hight Walker
Cobalt/gold (Co/Au) bimetallic nanoparticles are prepared by synthesizing Au via chemical reduction in the presence of pre-synthesized Co nanoparticles. Transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorption spectrometry, and a