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Search Publications by Angela R. Hight Walker

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Displaying 1 - 25 of 151

Synthesis of Mixed-Valent Lanthanide Sulfide Nanoparticles

August 23, 2021
Pricilla Glaser, Orlando Stewart, Rida Atif, Dane Asuigui, Joel Swanson, Adam Biacchi, Angela R. Hight Walker, Gregory Morrison, Hans-Conrad zur Loye, Sarah Stoll
In targeting reduced valence lanthanides, we report the first nanoparticle synthesis of the mixed-valent ferromagnets Eu3S4 and EuSm2S4. Using divalent lanthanide halides with bis(trimethylsilyl)sulfide and oleylamine, we prepared nanoparticles of EuS

The importance of international standards for the graphene community

April 8, 2021
Charles Clifford, Erlon H. Martins Ferreira, Toshiyuki Fujimoto, Jan Herrmann, Angela R. Hight Walker, Denis Koltsov, Christian Punckt, Lingling Ren, Gregory J. Smallwood, Andrew J. Pollard
If graphene and related 2D materials are to be used commercially, buyers need to have confidence in the measured properties of the material they obtain from suppliers. Scientists from international standards committees describe how the first joint ISO/IEC

Comparative study of multiwall carbon nanotube nanocomposites by Raman, SEM, and XPS measurement techniques

March 3, 2021
Yanmei Piao, Vipin Tondare, Chelsea S. Davis, Justin Gorham, Elijah Petersen, Jeffrey W. Gilman, Keana Scott, Andras Vladar, Angela R. Hight Walker
Substantial ongoing research efforts are investigating the production of novel composite material enhanced by the incorporation of nanomaterial fillers such as multiwall carbon nanotubes (MWCNTs). While the addition of MWCNTs have been shown to improve the

The joint automated repository for various integrated simulations (JARVIS) for data-driven materials design

November 12, 2020
Kamal Choudhary, Kevin Garrity, Andrew C. Reid, Brian DeCost, Adam Biacchi, Angela R. Hight Walker, Zachary Trautt, Jason Hattrick-Simpers, Aaron Kusne, Andrea Centrone, Albert Davydov, Francesca Tavazza, Jie Jiang, Ruth Pachter, Gowoon Cheon, Evan Reed, Ankit Agrawal, Xiaofeng Qian, Vinit Sharma, Houlong Zhuang, Sergei Kalinin, Ghanshyam Pilania, Pinar Acar, Subhasish Mandal, David Vanderbilt, Karin Rabe
The Joint Automated Repository for Various Integrated Simulations (JARVIS) is an integrated infrastructure to accelerate materials discovery and design using density functional theory (DFT), classical force-fields (FF), and machine learning (ML) techniques

Design and Engineering Colloidal Magnetic Particles for Nanoscale Thermometry

September 2, 2020
Adam J. Biacchi, Thinh Q. Bui, Cindi L. Dennis, Solomon I. Woods, Angela R. Hight Walker
Thermometry based on magnetic nanoparticles (MNPs) is an emerging technology that allows for remote temperature measurements throughout a volume that are impossible to achieve using conventional probe-based or optical methods. This metrology is based on

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

High-throughput Density Functional Perturbation Theory and Machine Learning Predictions of Infrared, Piezoelectric and Dielectric Responses

May 27, 2020
Kamal Choudhary, Kevin F. Garrity, Vinit Sharma, Adam J. Biacchi, Francesca M. Tavazza, Angela R. Hight Walker
In this work, combining high-throughput (HT) density functional perturbation theory and supervised machine learning approaches, we explored the territory of compounds with interesting infrared, piezoelectric and dielectric properties. We have computed Γ

Enhanced magnetization in proton irradiated Mn3Si2Te6 van der Waals crystals

April 28, 2020
L. M. Martinez, H. Iturriaga, R. Olmos, L. Shao, Y. Liu, Thuc Mai, C. Petrovic, Angela R. Hight Walker, S. R. Singamaneni
van der Waals (vdW) engineering of magnetism is a topic of increasing research interest in the community at present. We study the magnetic properties of quasi-two-dimensional layered vdW Mn3Si2Te6 (MST) crystals upon proton irradiation as a function of

Comparable Enhancement of TERS signals from WeSe2 on Chromium and Gold.

April 6, 2020
Albert Davydov, Sergiy Krylyuk, Angela R. Hight Walker, Bojan R. Ilic, Andrey Krayev, Ashish Bhattarai, Alan G. Joly, Matej Velicky, Patrick Z. El-Khoury
Plasmonic tip-sample junctions, at which the incident and scattered optical fields are localized and optimally enhanced, are often exploited to achieve ultrasensitive and highly spatially localized tip-enhanced Raman scattering (TERS). Recent work has

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

Dielectric properties of Nb_x}W_1-x}Se_2} alloys

December 16, 2019
Albert Rigosi, Heather M. Hill, Sergiy Krylyuk, Nhan V. Nguyen, Angela Hight Walker, Albert Davydov, David Newell
The growth of transition metal dichalcogenide (TMDC) alloys provides an opportunity to experimentally access information elucidating how optical properties change with gradual substitutions in the lattice compared with their pure compositions. In this work

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

Global alignment of solution-based single-wall carbon nanotube films via machine-vision controlled filtration

September 11, 2019
Jeffrey A. Fagan, Angela R. Hight Walker, Adam J. Biacchi, Joshua S. Walker, William D. Rice, Thomas Searles, Valerie A. Kuehl
Over the past decade, substantial progress has been made in the chemical processing (chiral enrichment, length sorting, handedness selectivity, and filling substance) of single- wall carbon nanotubes (SWCNTs). Recently, it was shown that large

Short-Range Charge Density Wave Order in TaS2

June 25, 2019
Jaydeep D. Joshi, Heather M. Hill, Sugata Chowdhury, Christos D. Malliakas, Francesca M. Tavazza, Utpal Chatterjee, Angela R. Hight Walker, Patrick M. Vora
2H-TaS2 undergoes a charge density wave (CDW) transition at T_CDW ~ 75 K, however key questions regarding the onset of CDW order remain under debate. In this study, we explore the CDW transition through a combination of temperature and excitation-dependent

Correlating anisotropic mobility and intermolecular phonons in organic semiconductors to investigate transient localization

March 19, 2019
Emily G. Bittle, Adam J. Biacchi, Lisa A. Fredin, Andrew A. Herzing, Thomas C. Allison, Angela R. Hight Walker, David J. Gundlach
Charge transport in organic semiconductors is governed by a mix of polaron hopping and band- like transport mechanisms. The energy of polaron hopping and formation are similar in magnitude to the energies of inter- and intra- molecular modes, which points

Metrological Assessment of Single-Walled Carbon Nanotube Materials by Optical Methods

March 1, 2019
Jeffrey A. Fagan, Angela R. Hight Walker, Ming Zheng, Lefebvre Jacques, Paul Finnie
This chapter discusses the metrology – i.e. the science of measurement – of single-wall carbon nanotubes (SWCNTs) with optical methods. Professor Mildred (“Millie”) Dresselhaus was a strong advocate for nanotube metrology and a pioneer in carbon nanotube

Raman Imaging of Surface and Sub-Surface Graphene Oxide in Fiber Reinforced Polymer Nanocomposites

March 1, 2019
Amber D. McCreary, Qi An, Aaron M. Forster, Kunwei Liu, Siyao He, Chris Macosko, Andreas Stein, Angela R. Hight Walker
The incorporation of nanofillers, such as graphene oxide (GO) into fiber reinforced polymer composites to improve their mechanical properties is a significant research area for a variety of industrial applications. However, to date there is no reliable

Defect Evolution of Ion-Exposed Single-Wall Carbon Nanotubes

January 3, 2019
Jana Kalbacova, Elias J. Garratt, Raul D. Rodriguez, Angela R. Hight Walker, Kevin A. Twedt, Jeffrey Fagan, Teresa I. Madeira, Jabez J. McClelland, Babak Nikoobakht, Dietrich R. Zahn
A systematic evaluation of defects is essential to understand and engineer device properties and applications. Raman spectroscopy is employed for the characterization of carbon nanomaterials in particular to quantitatively evaluate defects from the

Utilizing confocal laser scanning microscopy for rapid optical characterization of graphene

November 20, 2018
Vishal Panchal, Yanfei Yang, Guangjun Cheng, Jiuning Hu, Mattias Kruskopf, Chieh-I Liu, Albert Rigosi, Christos Melios, Angela R. Hight Walker, David B. Newell, Olga Kazakova, Randolph Elmquist
Confocal laser scanning microscopy (CLSM) is a non-destructive, highly-efficient optical characterization method for large-area analysis of graphene on different substrates, which can be applied in ambient air, does not require additional sample