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Search Publications by: Norman A. Sanford (Fed)

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Displaying 26 - 50 of 161

Measurement of the Electrostatic Edge Effect in Wurtzite GaN Nanowires

November 24, 2014
Author(s)
Alex Henning, Benjamin Klein, Kristine A. Bertness, Paul T. Blanchard, Norman Sanford, Yossi Rosenwaks
The electrostatic effect of the hexagonal corner on the electronic structure in wurtzite GaN nanowires (NWs) was directly measured using Kelvin probe force microscopy (KPFM). By correlating electrostatic simulations with the measured potential difference

GaN nanowire coated with atomic layer deposition of tungsten: a probe for near-field scanning microwave microscopy

September 25, 2014
Author(s)
Joel Weber, Paul T. Blanchard, Aric Sanders, Jonas Gertsch, Steven George, Samuel Berweger, Atif A. Imtiaz, Thomas Mitchell (Mitch) Wallis, Kris A. Bertness, Pavel Kabos, Norman A. Sanford, victor bright
We report on the fabrication of a GaN nanowire probe for near-field scanning microwave microscopy. The probe has a capacitive resolution of 0.03 fF, surpassing that of a commercial Pt tip. Imaging of MoS2 sheets found the probe to be immune to surface

Selective Area Growth of Ga- and N-polar GaN Nanowire Arrays on Non-Polar Si (111) Substrates

September 7, 2014
Author(s)
Matthew D. Brubaker, Shannon M. Duff, Todd E. Harvey, Paul T. Blanchard, Alexana Roshko, Aric W. Sanders, Norman A. Sanford
This study presents a technique for obtaining Ga- and N-polar Gallium Nitride nanowire (GaN NW) arrays on non-polar Si (111) substrates by use of polarity-controlled AlN/GaN buffer layers. AlN films are demonstrated to adopt Al-/N-polarity for N-/Al-rich

Imaging the p-n junction in a gallium nitride nanowire with a scanning microwave microscope

July 2, 2014
Author(s)
Atif A. Imtiaz, Thomas M. Wallis, Joel C. Weber, Kevin J. Coakley, Matthew D. Brubaker, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford
We used a broadband, atomic-force-microscope-based, scanning microwave microscope (AFM-SMM) to probe the axial dependence of the depletion in a GaN nanowire (NW) p-n junction structure. The NWs were c-axis oriented and grown by molecular beam epitaxy. The

Influence of morphology on current-voltage behavior of GaN nanowires

July 1, 2014
Author(s)
Paul T. Blanchard, Kristine A. Bertness, Matthew D. Brubaker, Todd E. Harvey, Aric W. Sanders, Norman A. Sanford
We demonstrate the effect that the different morphologies of MBE-grown GaN nanowires (NWs) can have upon current-voltage (I-V) behavior. Two main aspects of NW morphology were investigated. The first aspect was the NW diameter, dNW. For single-crystal Si

Establishing an upper bound on contact resistivity of ohmic contacts to n-GaN nanowires

April 1, 2014
Author(s)
Paul T. Blanchard, Kristine A. Bertness, Todd E. Harvey, Norman A. Sanford
Contact resistivity ρ c is an important figure of merit in evaluating and improving the performance of electronic and optoelectronic devices. Due to the small size, unique morphology, and uncertain transport properties of semiconductor nanowires (NWs)

Characterization of InGaN quantum disks in GaN nanowires

March 4, 2014
Author(s)
Alexana Roshko, Roy H. Geiss, John B. Schlager, Matthew D. Brubaker, Kristine A. Bertness, Norman A. Sanford, Todd E. Harvey
Catalyst-free GaN nanowires with InGaN quantum disks (QDs) were characterized by scanning/transmission elec-tron microscopy (S/TEM) and photoluminescence. A va-riety of structures, from QDs with large strain fields to apparently strain free QDs were

Characterization of InGaN quantum disks in GaN nanowires

February 27, 2014
Author(s)
Alexana Roshko, Roy H. Geiss, John B. Schlager, Matthew D. Brubaker, Kristine A. Bertness, Norman A. Sanford, Todd E. Harvey
Catalyst-free GaN nanowires with InGaN quantum disks (QDs) were characterized by scanning/transmission electron microscopy (S/TEM) and photoluminescence. A variety of structures, from QDs with large strain fields to apparently strain free QDs were observed

Laser-assisted atom probe tomography of MBE grown GaN nanowire heterostructures

February 24, 2014
Author(s)
Norman A. Sanford, Paul T. Blanchard, Matthew D. Brubaker, Kristine A. Bertness, John B. Schlager, R Kirchofer, David R. Diercks, Brian Gorman
Laser-assisted atom probe tomography (L-APT) was performed on GaN nanowires (NWs) and axial GaN/InGaN nanowire heterostructures. All samples were grown by MBE on Si(111) substrates. The laser pulse energy (PE) at 355 nm used in L-APT analysis of GaN NWs

In situ temperature measurements for selective epitaxy of GaN nanowires

February 17, 2014
Author(s)
Kristine A. Bertness, Matthew D. Brubaker, Todd E. Harvey, Shannon M. Duff, Aric W. Sanders, Norman A. Sanford
We demonstrate with spatially resolved, in situ temperature measurements and ex situ reflectance measurements that differences in appearance for masked and unmasked surfaces on patterned growth substrates arise from wavelength-dependent emissivity

Gallium Nitride Nanowire Probe for Near-Field Scanning Microwave Microscopy

January 15, 2014
Author(s)
Joel C. Weber, Paul T. Blanchard, Aric W. Sanders, Atif A. Imtiaz, Thomas M. Wallis, Kevin J. Coakley, Kristine A. Bertness, Pavel Kabos, Norman A. Sanford, Victor M. Bright
We report on the fabrication of a GaN nanowire probe for near-field scanning microwave microscopy. A single nanowire was Pt-bonded to a commercial Si cantilever prior to evaporation of a Ti/Al coating to provide a microwave signal pathway. Testing over a

Atom probe tomography evaporation behavior of C-axis GaN nanowires: Crystallographic, stoichiometric, and detection efficiency aspects

November 13, 2013
Author(s)
Norman A. Sanford, David R. Diercks, Brian Gorman, R Kirchofer, Kristine A. Bertness, Matthew D. Brubaker
The field evaporation behavior of c-axis GaN nanowires was explored in two different laser-pulsed atom probe tomography (APT) instruments. Transmission electron microscopy imaging before and after atom probe tomography analysis was used to assist in

On the Field Evaporation Behavior of c-axis GaN Nanowires in Laser-Pulsed Atom Probe Tomography

June 26, 2013
Author(s)
Matthew D. Brubaker, Kristine A. Bertness, Norman A. Sanford, Brian Gorman, David R. Diercks, R Kirchofer
GaN has seen use in many applications such as photovoltaics, blue and ultraviolet lasers, and light-emitting diodes with additional research into expanded and new applications. GaN in the form of nanowires present additional possibilities due to their high

Radio-Frequency and DC Electrical Characterization on a Modular MEMS Mechanical Test Platform for Nanomaterials

June 16, 2013
Author(s)
J. J. Brown, Thomas Mitchell (Mitch) Wallis, Pavel Kabos, Kristine A. Bertness, Norman Sanford, Victor Bright
In order to enable radio frequency (RF) data collection from a micromechanical system designed to strain nanomaterials, a coplanar electrical waveguide has been integrated with an actuated microscale stage. RF (100 MHz to 20 GHz) admittance measurements

Studies of photoconductivity and FET behavior in examining drift mobility, surface depletion, and transient effects in Si-doped GaN nanowires examined in vacuum and air

May 3, 2013
Author(s)
Norman A. Sanford, Lawrence H. Robins, Paul T. Blanchard, K. Soria, B. Klein, Kristine A. Bertness, John B. Schlager, Aric W. Sanders
Variable intensity photoconductivity (PC) performed under vacuum at 325 nm was used to estimate drift mobility and negative surface charge density sigma for c-axis oriented Si-doped GaN nanowires (NWs). In this approach we assumed that sigma was

Spatially-Resolved Dopant Characterization with a Scanning Microwave Microscope

March 25, 2013
Author(s)
Thomas M. Wallis, Atif A. Imtiaz, Alexandra E. Curtin, Pavel Kabos, Matthew D. Brubaker, Norman A. Sanford, Kristine A. Bertness
The scanning microwave microscope (SMM) is a tool for spatially-resolved microwave characterization of nanoelectronic materials and devices. The microscope incorporates a sharp, near-field probe, which measures local changes in reflected microwave signals

Gallium Nitride Nanowires for On-Chip Optical Interconnects on Ex-Situ Substrates

January 16, 2013
Author(s)
Matthew D. Brubaker, Paul T. Blanchard, John B. Schlager, Aric W. Sanders, Alexana Roshko, Shannon M. Duff, Jason Gray, Victor M. Bright, Norman A. Sanford, Kristine A. Bertness
In this letter we report on the fabrication, device characteristics, and optical coupling of a two-nanowire device comprising light-emitting diode and photoconductive GaN nanowires. Axial p-n junction GaN nanowires were grown by molecular beam epitaxy

Low-frequency noise in gallium nitride nanowire mechanical resonators

December 7, 2012
Author(s)
Jason Gray, Kristine A. Bertness, Norman Sanford, Charles T. Rogers
We report on the low-frequency 1/f (flicker) parameter noise displayed by the resonance frequency and resistance of doubly clamped c-axis gallium nitride nanowire (NW) mechanical resonators. The resonators are electrostatically driven and their mechanical

Temperature-dependent mechanical-resonance frequencies and damping in ensembles of gallium nitride nanowires

October 22, 2012
Author(s)
Kristine A. Bertness, Norman A. Sanford, J. R. Montague, H.S. Park, Victor M. Bright, Charles T. Rogers
We have measured singly clamped cantilever mechanical-resonances in ensembles of as-grown gallium nitridenanowires (GaN NWs), from 12 K to 320 K. Resonance frequencies are approximately linearly dependent on temperature near 300 K with relative shifts of

Optimization of Dispersion and Surface Pretreatment for Single GaN Nanowire Devices

September 28, 2012
Author(s)
Norman A. Sanford, Kristine A. Bertness, Andrew M. Herrero
The correlation of residual contamination with void formation at the contact/SiO2 interface for single GaN NW devices was investigated. The morphology at the metal/SiO2 interface was observed by removing the annealed Ni/Au films from the SiO2 with carbon

Noncontact measurement of charge carrier lifetime and mobility in GaN nanowires

August 27, 2012
Author(s)
Christopher M. Dodson, Patrick Parkinson, Kristine A. Bertness, Hannah J. Joyce, Laura M. Herz, Norman Sanford, Michael B. Johnston
The first noncontact photoconductivity measurements of gallium nitride nanowires (NWs) are presented, revealing a high crystallographic and optoelectronic quality achieved by use of catalyst-free molecular beam epitaxy. In comparison with bulk material

Microwave Measurements and Systematic Circuit-Model Extraction of Nanowire Metal Semiconductor Field Effect Transistors

August 24, 2012
Author(s)
Dazhen Gu, Thomas M. Wallis, Pavel Kabos, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford
We present detailed on-wafer scattering parameter measurements and equivalent circuit modeling of metal semiconductor field effect transistor (MESFET) that incorporates a GaN nanowire (NW). A systematic procedure is established to extract intrinsic model

Microwave measurements and systematic circuit-model extraction of nanowire metal semiconductor field-effect transistors

August 24, 2012
Author(s)
Dazhen Gu, Thomas M. Wallis, Pavel Kabos, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford
We present detailed on-wafer scattering parameter measurements and equivalent circuit modeling of metal semiconductor field effect transistor (MESFET) that incorporates a GaN nanowire (NW). A systematic procedure is established to extract intrinsic model