Sandra C. Hernández

United States Naval Research Laboratory

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Co-Authors

Scott G. Walton

United States Naval Research Laboratory

Virginia D. Wheeler

United States Naval Research Laboratory

D. Kurt Gaskill

United States Naval Research Laboratory

Jeremy T. Robinson

United States Naval Research Laboratory

Nosang V. Myung

University of Notre Dame

Charles R. Eddy

Office of Naval Research

Rachael L. Myers‐Ward

United States Naval Research Laboratory

David R. Boris

United States Naval Research Laboratory

Paul E. Sheehan

Defense Advanced Research Projects Agency

Anindya Nath

GlobalFoundries (United States)

Cooperative Institutions

United States Naval Research Laboratory

United States Navy

University of Maryland, College Park

IBM Research - Thomas J. Watson Research Center

Lawrence Berkeley National Laboratory

University of California, Riverside

National Academies of Sciences, Engineering, and Medicine

K Lab (United States)

University of California, Berkeley

University of Virginia

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Single Polypyrrole Nanowire Ammonia Gas Sensor

Electroanalysis (2007)

Sandra C. Hernández Debangshu Chaudhuri Wilfred Chen Nosang V. Myung Ashok Mulchandani

Abstract We report the synthesis, electrical characterization and ammonia gas sensing with single nanowire of conducting polypyrrole. Three hundred nanometer in diameter and 50 to 60 μm long polypyrrole nanowires were synthesized by chemical polymerization inside SiO 2 coated alumina membranes. Temperature dependent electrical resistance studies established that the chemically synthesized nanowires were more ordered compared to electrochemically synthesized nanowires. We further demonstrated that gas sensors based on single polypyrrole nanowire exhibited good sensitivity towards ammonia, and provided a reliable detection at concentration as low as approximately 40 ppm.

Polypyrrole

Ammonia gas

Nanometre

10.1002/elan.200703933

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Citations (175)

Hybrid ZnO/SWNT Nanostructures Based Gas Sensor

Electroanalysis (2012)

Sandra C. Hernández James Kakoullis Jae Hong Lim Syed Mubeen Carlos M. Hangarter

Abstract Zinc oxide (ZnO) nanoparticles decorated single walled carbon nanotubes (SWNTs) were electrochemically synthesized where the deposition conditions were systematically explored to tailor the size, density, and microstructure of the ZnO nanoparticles and correlated to the gas sensing performance. Room temperature conductometric detection of various analytes including CO, CO 2 , NO 2 , NH 3 , SO 2 , H 2 S with ZnO/SWNT hybrid nanostructures demonstrated uncharacteristic selectivity towards H 2 S with little to no response for the other analytes examined. Optimal ZnO/SWNTs gas sensor devices showed a significantly increased in H 2 S sensitivity over unfunctionalized SWNT networks (i.e. 4.96 % per ppm V vs. 0.225 % ppm V ) with a lower detection limit in the ppb range. Additionally, the H 2 S sensing performance was greatly improved by enhancing the crystallinity of ZnO nanoparticles.

10.1002/elan.201200135

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Citations (22)

Selective recognition of xylene isomers using ZnO–SWNTs hybrid gas sensors

The Analyst (2012)

Sandra C. Hernández Carlos M. Hangarter Ashok Mulchandani Nosang V. Myung

We demonstrate a hybrid ZnO nanoparticle decorated SWNT network device that can conductometrically differentiate between xylene isomers at room temperature with minimal interference from background VOCs. Field effect transistor measurements are conducted to identify the sensing mechanism which is attributed to enhanced SWNT transduction of chemical interaction with ZnO surfaces.

10.1039/c2an35168d

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Citations (13)

New insights in electrochemical surface oxidation enhanced raman scattering

Luis Romay Sandra C. Hernández Martín Pérez Estébanez Juan Víctor Perales Rondón Aránzazu Heras

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Electrochemically Prepared Polycrystalline Copper Surface for the Growth of Hexagonal Boron Nitride

Crystal Growth & Design (2017)

Karthik Sridhara Boris N. Feigelson James A. Wollmershauser Jennifer K. Hite Anindya Nath

The controlled and reproducible growth of hexagonal boron nitride (h-BN) by chemical vapor deposition on polycrystalline copper foil substrates remains a challenge as typical growth surfaces contain microscopic ridges (height ≈ 100 μm) arising from the foil manufacturing process. In this work, we report a method to prepare commercially cold-rolled polycrystalline copper substrates for greatly improved growth of h-BN by a combination of thermal annealing in a reducing environment and electrochemical polishing to create an excellent surface that enables control of BN nucleation sites. We report a root mean square roughness of ∼1.2 nm for the Cu substrate after electropolishing and a reduction of nucleation sites along with enlargement of h-BN crystals with this combined approach. We also assess the potential role of surface features that exist on the Cu surface as nucleation sites. The development of an electrochemical process to prepare two-dimensional (2D) material growth substrates and demonstration of greatly improved growth of 2D materials directly point to more pragmatic large scale processing of 2D materials since such techniques are already utilized in large scale industrial processing.

Electropolishing

10.1021/acs.cgd.6b01665

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Citations (11)

Plasma-based chemical modification of epitaxial graphene with oxygen functionalities

Surface and Coatings Technology (2013)

Sandra C. Hernández Virginia D. Wheeler M. S. Osofsky Glenn G. Jernigan V. Karthik Nagareddy

Chemical modification

Surface Modification

10.1016/j.surfcoat.2013.11.015

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Citations (20)

Fabrication and test of prototype ring magnets for the ALS [Advanced Light Source]

J. Tanabe R. Avery Ryan Caylor M.I. Green E. Hoyer

Prototype Models for the Advanced Light Source (ALS) Booster Dipole, Quadrupole and Sextupole and the Storage Ring Gradient Magnet, Quadrupole and Sextupole have been constructed. The Booster Magnet Prototypes have been tested. The Storage Ring Magnets are presently undergoing tests and magnetic measurements. This paper reviews the designs and parameters for these magnets, briefly describes features of the magnet designs which respond to the special constraints imposed by the requirements for both accelerator rings, and reviews some of the results of magnet measurements for the prototype. 13 refs., 7 figs., 1 tab.

Booster (rocketry)

Quadrupole magnet

Dipole magnet

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Electron Beam Generated Plasmas for Ultra Low T_eProcessing

ECS Journal of Solid State Science and Technology (2015)

Scott G. Walton David R. Boris Sandra C. Hernández Evgeniya H. Lock Tz. B. Petrova

The Naval Research Laboratory (NRL) has developed a processing system based on an electron beam-generated plasma. Unlike conventional discharges produced by electric fields (DC, RF, microwave, etc.), ionization is driven by a high-energy (∼ few keV) electron beam, an approach that can be attractive to atomic layer processing applications. In particular, high electron densities (1010- 1011 cm−3) can be produced in electron beam generated plasmas, where the electron temperature remains between 0.3 and 1.0 eV. Accordingly, a large flux of ions can be delivered to substrate surfaces with kinetic energies in the range of 1 to 5 eV. This provides the potential for controllably etching and/or engineering both the surface morphology and chemistry with monolayer precision. This work describes the electron beam driven plasma processing system, with particular attention paid to system characteristics and the ability to control the generation and delivery of ions to the surface and their energies.

Plasma Processing

10.1149/2.0071506jss

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Citations (88)

Template-Directed Electrodeposition of Iron-Palladium Nanowires and Their Electrical Transport and Sensing Properties

Journal of The Electrochemical Society (2017)

Sandra C. Hernández Carlos M. Hangarter Jong Ryoul Kim Yong‐Ho Choa Nosang V. Myung

Template-directed electrodeposition was utilized to fabricate FexPd1-x nanowires where the dimension was controlled by template pore size (i.e., 30 and 200 nm) whereas the composition was tuned by varying the Fe+2/Pd+2 metal ion ratio in ammonium chloride baths at fixed deposition current density of 5 mA cm−2. A wide range of composition (i.e., Pd-rich, near equiatomic, and Fe-rich) were successfully fabricated and their magnetic properties were examined. Additionally, single nanowire was also integrated on to microfabricated gold electrodes by magnetic alignment, followed by post-annealing in a reducing environment to make good electrical contacts. Assembled single nanowire was utilized to determine their electrical transport properties including temperature-dependent resistance (TCR) and magnetoresistance (MR). Additionally, the feasibility of FexPd1-x nanowire based hydrogen sensor was examined at room temperature.

Atmospheric temperature range

10.1149/2.0091802jes

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Citations (2)

In Situ Study of Fluorine-Functionalized and Tri-Methyl Aluminum Dosed Epitaxial Graphene on SiC(0001)

Bulletin of the American Physical Society (2015)

Zachary R. Robinson Virginia D. Wheeler Sandra C. Hernández Glenn G. Jernigan Rachael L. Myers‐Ward

Fluorine

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