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Search Publications by: Jeffrey Simpson (Assoc)

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Displaying 1 - 19 of 19

Distinct magneto-Raman signatures of spin-flip phase transitions in CrI3

August 3, 2020
Amber D. McCreary, Thuc T. Mai, Franz Utermohlen, Jeffrey R. Simpson, Kevin F. Garrity, Xiaozhou Feng, Dmitry Shcherbakov, Yanglin Zhu, Jin Hu, Daniel Weber, Kenji Watanabe, Takashi Taniguchi, Joshua Goldberger, Zhiqiang Mao, Chun Ning Lau, Yuanming Lu, Nandini Trivedi, Rolando Valdes Aguilar, Angela R. Hight Walker
The discovery of 2-dimensional (2D) materials, such as CrI3, that retain magnetic ordering down to monolayer thickness, and even more have layer-dependent magnetic properties has led to a plethora of research in 2D magnetism. Here, we report a magneto

Quasi-two-dimensional magnon identification in antiferromagnetic FePS3 via magneto-Raman spectroscopy

February 18, 2020
Amber D. McCreary, Jeffrey R. Simpson, Thuc T. Mai, Robert D. McMichael, Jason E. Douglas, Nicholas P. Butch, Cindi L. Dennis, Rolando Valdes Aguilar, Angela R. Hight Walker
Recently it was discovered that van der Waals-bonded magnets retain long range magnetic ordering even down to a monolayer thickness, opening many avenues in fundamental physics and potential applications of these fascinating materials. One example is FePS3

Polarization-resolved Raman spectroscopy of \alpha-RuCl3 and evidence of room temperature two-dimensional magnetic scattering

October 14, 2019
Thuc T. Mai, Amber D. McCreary, P. Lampen-Kelley, Nicholas P. Butch, Jeffrey R. Simpson, J.-Q. Yan, S. E. Nagler, D. Mandrus, Angela R. Hight Walker, Rolando Valdes Aguilar
Polarization-resolved Raman spectroscopy was performed and analyzed from large, high quality, mono-domain single crystal of \alpha-RuCl3, a proximate Kitaev quantum spin liquid. Spectra were collected with laser polarizations parallel and perpendicular to

Alkane Encapsulation Induces Strain in Small Diameter Single-Wall Carbon Nanotubes

May 4, 2018
Jason K. Streit, Jochen I. Campo, Chad R. Snyder, Ming Zheng, Jeffrey R. Simpson, Angela R. Hight Walker, Jeffrey Fagan
Encapsulation of linear alkane molecules in the endohedral volumes of small diameter single- wall carbon nanotubes (SWCNTs) is shown to induce diameter dependent strain on the hexagonal lattice of carbon atoms composing the tubular structure. For the

Intricate Resonant Raman Response in Anisotropic ReS2

August 18, 2017
Amber McCreary, Jeffrey R. Simpson, Yuanxi Wang, Daniel Rhodes, Kazunori Fujisawa, Luis Balicas, Madan Dubey, Vincent H. Crespi, M. Terrones, Angela R. Hight Walker
Rhenium disulfide is an exciting material due to its strong in-plane anisotropy, thus offering an additional physical parameter that can be tuned for advanced applications. ReS2 provides a major advantage for optoelectronics as it is both stable in air and

Enhancing Single-Wall Carbon Nanotube Properties Through Controlled Endohedral Filling

May 10, 2016
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
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

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

December 30, 2013
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
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

Carbon Nanotubes: Measuring Dispersion and Length

August 26, 2010
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

Centrifugal Length Separation of Carbon Nanotubes

October 1, 2008
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

Optical Anisotropy of Semiconducting Single-Wall Carbon Nanotubes

January 1, 2007
Jeffrey Fagan, Erik K. Hobbie, Jeffrey R. Simpson, Lee J. Richter, Idan Mandelbaum, Vardhan Bajpai, Derek L. Ho, Barry J. Bauer, Angela HightWalker, Ryan Raffaelle
We measure the full optical anisotropy of individual semiconducting single-wall carbon nanotubes (SWNTs). Dispersion of aligned SWNTs in stretched polymer films is confirmed with small-angle scattering and near-infrared fluorescence spectroscopy. By

Comparative Measures of Single Wall Carbon Nanotube Dispersion

September 14, 2006
Jeffrey A. Fagan, Brian Landi, Idan Mandelbaum, Vardhan Bajpai, Barry J. Bauer, Kalman D. Migler, Jeffrey R. Simpson, Angela R. Hight Walker, Ryan Raffaelle, Erik K. Hobbie
Model polymer composites of DNA wrapped single-wall carbon nanotubes (SWNTs) dispersed in polyacrylic acid are used for a systematic comparison of the different metrologies currently used to evaluate SWNT dispersion. Application of a pH-controlled

Quantitative, Interactive Measurement of Tissue Engineering Scaffold Structure Using Immersive Visualization

January 1, 2006
Jeffrey Fagan, Erik K. Hobbie, Brian Landi, Idan Mandelbaum, Vardhan Bajpai, Barry J. Bauer, Kalman D. Migler, Jeffrey R. Simpson, Angela R. Hight Walker, Ryan Raffaelle
At NIST, we are using new approaches to better understand and quantify the structure of tissue engineering scaffolds. This approach uses immersive visualization (IV) and is inherently three dimensional, multivariate and interactive, providing real-time