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Search Publications by: Norman A. Sanford (Fed)

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Displaying 51 - 75 of 161

Microstructure evolution and development of annealed Ni/Au contacts to GaN nanowires

August 21, 2012
Author(s)
Andrew M. Herrero, Paul T. Blanchard, Aric W. Sanders, Matthew D. Brubaker, Norman A. Sanford, Alexana Roshko, Kristine A. Bertness
The development of Ni/Au contacts to Mg-doped GaN nanowires (NWs) is examined. Current-voltage (I-V) measurements of these Mg-doped nanowire devices frequently exhibit a strong degradation after annealing in N 2/O 2. This degradation originates from the

Photoluminescence Polarization in Strained GaN/AlGaN Core/Shell Nanowires

August 17, 2012
Author(s)
G. Jacopin, L. Rigutti, S. Bellei, P. Lavenus, F. H. Julien, Albert Davydov, Denis Tsvetkov, Kristine A. Bertness, Norman Sanford, John B. Schlager, M. Tchemycheva
The polarization properties of GaN/AlGaN core/shell nanowire (NW) heterostructures have been investigated using polarization resolved micro-photoluminescence (µ-PL) and interpreted in terms of a strain dependent 6x6 k.p theoretical model. The NW

A near-field scanning microwave microscope for characterization of inhomogeneous photovoltaics

August 10, 2012
Author(s)
Joel C. Weber, Kristine A. Bertness, John B. Schlager, Norman A. Sanford, Atif A. Imtiaz, Thomas M. Wallis, Pavel Kabos, Kevin J. Coakley, Victor Bright, Lorelle M. Mansfield
We present a near field scanning microwave microscope (NSMM) optimized for imaging photovoltaic samples. Our system incorporates a cut Pt-Ir tip inserted into an open ended coaxial cable to form a weak resonator, allowing the microwave reflection S11

Sensing Trace Amounts of Nitro-Aromatic Explosives using Nanowire-Nanocluster Hybrids

August 1, 2012
Author(s)
Geetha G. Aluri, Abhishek Motayed, Albert Davydov, Vladimir P. Oleshko, Kristine A. Bertness, Norman A. Sanford
The threat of terrorism and the need for homeland security calls for advanced technologies to detect the concealed explosives safely and efficiently. We demonstrated highly sensitive and selective detection of traces of nitro-aromatic explosive compounds

Anisotropic Field Evaporation of Diatomic Species from Oxides and Nitrides

May 21, 2012
Author(s)
Matthew D. Brubaker, David R. Diercks, R Kirchofer, Kristine A. Bertness, Norman A. Sanford, Brian Gorman
Recent work using laser-assisted atom probe tomography on non-metallic materials has indicated that for many data collection conditions, anisotropic evaporation can occur. In some cases this can be attributed to a high laser energy leading to uneven

Methanol, Ethanol, and Hydrogen Sensing using Metal-Oxide and Metal (TiO subscript 2-Pt) Composite Nanoclusters on GaN Nanowires: A New Route towards Tailoring the Selectivity of Nanowire-Nanocluster based Chemical Sensors.

May 12, 2012
Author(s)
Geetha G. Aluri, Abhishek Motayed, Albert Davydov, Vladimir Oleshko, Kristine A. Bertness, Norman Sanford, Mulpuri V. Rao
We demonstrate a new method for tailoring the selectivity of chemical sensors using nanowires decorated with multicomponent nanoclusters (metal and metal-oxide)-based hybrid sensors. In the present study we demonstrate the change of selectivity of titanium

Catalyst-free GaN Nanowires as Nanoscale Light Emitters

March 1, 2012
Author(s)
Kristine A. Bertness, Norman A. Sanford, John B. Schlager, Alexana Roshko, Todd E. Harvey, Paul T. Blanchard, Matthew D. Brubaker, Andrew M. Herrero, Aric W. Sanders
Catalyst-free growth of GaN nanowires with molecular beam epitaxy produces material of exceptionally high quality with long minority carrier lifetimes and low surface recombination velocity. The nanowires grow by thermodynamic driving forces that enhance

MOSFETs made from GaN nanowires with fully conformal cylindrical gates

December 2, 2011
Author(s)
Paul T. Blanchard, Kristine A. Bertness, Todd E. Harvey, Aric W. Sanders, Norman A. Sanford, Steven M. George, Dragos Seghete
We report novel metal-oxide-semiconductor field effect transistors (MOSFETs) based on individual gallium nitride (GaN) nanowires with fully conformal cylindrical gates. The W/Al 2O 3 gates were deposited by atomic layer deposition. Reverse-bias breakdown

Capacitive readout technique for studies of dissipation in GaN nanowire mechanical resonators

November 11, 2011
Author(s)
Kristine A. Bertness, Joshua R. Montague, Norman A. Sanford, Victor Bright, Charles T. Rogers
A variable-temperature, homodyne reflectometry measurement technique for detecting nanoscale mechanical motion has recently been developed. We have extended this technique to make the first all-electrical measurements of an ensemble of as-grown, c-axis

Gallium nitride nanowires achieve crystalline perfection

October 25, 2011
Author(s)
Kristine A. Bertness, Norman A. Sanford, John B. Schlager
A new method of growing a common semiconductor provides an avenue for fabricating perfect crystals in a form that takes advantage of their unique optical, electrical, and mechanical properties.

Homoepitaxial n-core: p-shell gallium nitride nanowires: HVPE overgrowth growth on MBE nanowires

October 25, 2011
Author(s)
Aric Sanders, Paul T. Blanchard, Kristine A. Bertness, Matthew D. Brubaker, Ann Chiaramonti Debay, Christopher M. Dodson, Todd E. Harvey, Andrew M. Herrero, Devin M. Rourke, John B. Schlager, Norman Sanford, Albert Davydov, Abhishek Motayed, Denis Tsvetkov
We present the homoepitaxial growth of p-type, magnesium-doped gallium nitride shells using halide vapor phase epitaxy on n-type gallium nitride nanowires grown by plasma-assisted molecular beam epitaxy. Scanning electron microscopy shows clear dopant

Abstract of the presentation: Position- and polarization- resolved microphotoluminescence of GaN/AlGaN core-shell nanowires

October 17, 2011
Author(s)
Albert Davydov, G. Jacopin, S. Bellei, Denis Tsvetkov, Kristine A. Bertness, L. Rigutti, Norman A. Sanford, John B. Schlager, M. Tchernycheva, F. H. Julien
Over the past decade, core-shell nanowires (NWs) have been intensively used as the building blocks of novel optoelectronic devices as solar cells [1], LEds [2], naolasers [3]. Indeed, this geometry not only allows to passivate surface states, but also

Effect of AlN Buffer Layer Properties on the Morphology and Polarity of GaN Nanowires Grown by Molecular Beam Epitaxy

September 8, 2011
Author(s)
Matthew D. Brubaker, Kristine A. Bertness, Norman A. Sanford, Albert Davydov, Igor Levin, Devin M. Rourke, Victor M. Bright
Low temperature AlN buffer layers grown by plasma-assisted Molecular Beam Epitaxy (MBE) on Si (111) were found to significantly affect the subsequent growth morphology of GaN nanowires. The AlN buffer layers exhibited nanowire-like columnar protrusions

Catalyst-free GaN nanowire growth and optoelectronic characterization

August 19, 2011
Author(s)
Kristine A. Bertness, Norman A. Sanford, John B. Schlager
We discuss the present state-of-the-art concerning the growth mechanism, optical luminescence and electrical properties for GaN nanowires grown with catalyst-free molecular beam epitaxy. These nanowires are essentially defect-free and display long

Gallium nitride nanowire electromechanical resonators with piezoresistive readout

August 11, 2011
Author(s)
Kristine A. Bertness, Jason M. Gray, Norman A. Sanford, Charles T. Rogers
We report on the fabrication, piezoresistive readout, and frequency response of doubly-clamped c-axis gallium nitride (GaN) nanowire (NW) resonators that show mechanical quality factors exceeding 10,000. The devices are fabricated using a combination of

GaN Nanowires Grown by Molecular Beam Epitaxy

August 1, 2011
Author(s)
Kristine A. Bertness, Norman A. Sanford, Albert Davydov
The unique properties of GaN nanowires grown by molecular beam epitaxy are reviewed. These properties include the absence of residual strain, exclusion of most extended defects, long photoluminescence lifetime, low surface recombination velocity,and high

Highly Selective GaN-nanowire/TiO2-nanocluser Hybrid Sensors for Detection of Benzene and Related Environment Pollutants

July 22, 2011
Author(s)
Geetha G. Aluri, Abhishek Motayed, Albert Davydov, Vladimir Oleshko, Kristine A. Bertness, Norman Sanford
Nanowire-nanocluster hybrid chemical sensors were realized by functionalizing gallium nitride (GaN) nanowires with titanium dioxide (TiO2) nanoclusters for selectively sensing benzene and other related aromatic compounds. Hybrid sensor devices were

Electrical Characterization of Photoconductive GaN Nanowire Devices from 50 MHz to 33 GHz

July 1, 2011
Author(s)
Thomas M. Wallis, Dazhen Gu, Atif A. Imtiaz, Pavel Kabos, Paul T. Blanchard, Norman A. Sanford, Kristine A. Bertness, Christpher Smith
The electrical response of two-port., photoconductive GaN nanowire devices was measured from 50 MHz to 33 GHz. The admittance of individual contacted nanowires showed an increase on the order of 10% throughout the measured frequency range after exposure to

GaN nanowires grown by molecular beam epitaxy

July 1, 2011
Author(s)
Kristine A. Bertness, Norman A. Sanford, Albert Davydov
The unique properties of GaN nanowires grown by molecular beam epitaxy are reviewed. These properties include defect-free growth mode with no residual strain, long photoluminescence lifetime, low surface recombination velocity and high mechanical quality

Deembedding parasitic elements of GaN nanowire MESFETs by use of microwave measurements

June 3, 2011
Author(s)
Dazhen Gu, Thomas M. Wallis, Paul T. Blanchard, SangHyun S. Lim, Atif A. Imtiaz, Kristine A. Bertness, Norman A. Sanford, Pavel Kabos
We present a deembedding roadmap for extracting parasitic elements of a nanowire (NW) MESFET device from full two-port scattering-parameter measurements in the frequency range from 0.1 GHz to 25 GHz. The NW MESFET is integrated in a microwave coplanar

Analysis of high-Q, gallium nitride nanowire resonators in response to deposited thin films

January 1, 2011
Author(s)
J. R. Montague, M. Dalberth, J. M. Gray, D. Seghete, Kristine A. Bertness, S M. George, Victor M. Bright, Charles T. Rogers, Norman Sanford
Gallium nitride nanowires (GaN-NWs) are systems of interest for mechanical resonance-based sensors due to their small mass and, in the case of c-axis NWs, high mechanical quality (Q) factors of 10,000-100,000. We report on singly-clamped NW mechanical