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Search Publications by: Kris A. Bertness (Fed)

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Displaying 26 - 50 of 351

Raman spectroscopy for dopant optimization in GaN nanowire light-emitting diodes

May 1, 2018
Author(s)
Kristine A. Bertness, Bryan T. Spann, Matthew D. Brubaker, Todd E. Harvey, Paul T. Blanchard
We apply Raman spectroscopy to optimize both n-type and p-type doping in GaN nanowire light- emitting diodes (LEDs) grown with selective epitaxy on Si(111) with molecular beam epitaxy. N-type doping with Si is characterized using the peak shift in the LO

Spectral tuning of localized surface phonon-polariton modes in selective area epitaxy GaN nanowire arrays

May 1, 2018
Author(s)
Bryan T. Spann, J. Ryan Nolen, Matthew D. Brubaker, Thomas G. Folland, Chase T. Ellis, Joseph G. Tischler, Todd E. Harvey, Joshua D. Caldwell, Kristine A. Bertness
Polar semiconductor materials, such as GaN, InP, SiC et al., offer a basis to manufacture innovative long-wavelength photonic devices.1 Such semiconductors can support propagating and localized surface phonon-polariton (SPhP) resonances that provide highly

GaN Nanowire MOSFET with Near-Ideal Subthreshold Slope

December 21, 2017
Author(s)
Kristine A. Bertness, Wenjun Li, Matthew D. Brubaker, Bryan T. Spann, Patrick Fay
Top-gated GaN nanowire MOSFETs using Al2O3 as gate oxide have been experimentally demonstrated. The fabricated devices exhibit a minimum subthreshold slope of 60 mV/dec, an average subthreshold slope of 68 mV/dec over three decades of drain current, drain

Dimensional Measurement of Nanostructures with Scanning Electron Microscopy

September 20, 2017
Author(s)
Kristine A. Bertness
Scanning electron microscopy (SEM) is widely used for the measurement of dimensions of nanostructures. This document describes the calibration of SEM magnification using the ASTM E766-14 practice with NIST Reference Material (RM) 8820 and the calculation

Lithographic sonication patterning of large area nanopillar forests

July 27, 2017
Author(s)
Joel C. Weber, Matthew D. Brubaker, Thomas M. Wallis, Kristine A. Bertness
This paper demonstrates a highly-scalable, material-independent method for patterning nanopillar forests known as lithographic sonication patterning. Through contact lithography, patterns with dimensions down to 3 υm were written across a 3-inch silicon

Comparison of CBED and ABF Atomic Imaging for GaN Polarity Determination

November 8, 2016
Author(s)
Alexana Roshko, Matthew D. Brubaker, Paul T. Blanchard, Kristine A. Bertness, Todd E. Harvey, Igor Levin, R.H. Geiss
A comparison of two electron microscopy techniques used to determine the polarity of GaN nanowires is presented. The techniques are convergent beam electron diffraction (CBED) in TEM mode and annular bright field (ABF) imaging in aberration corrected STEM

Raman spectroscopy based measurements of carrier concentration in n-type GaN nanowires grown by plasma-assisted molecular beam epitaxy

September 30, 2016
Author(s)
Lawrence H. Robins, Elizabeth Horneber, Norman A. Sanford, Kristine A. Bertness, John B. Schlager
The carrier concentration in ensembles of n-type GaN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy was determined by curve-fitting analysis of Raman spectra, based on modeling of the carrier concentration dependence of the longitudinal

Spontaneous growth of GaN nanowire nuclei on N- and Al-polar AlN: A piezoresponse force microscopy study of crystallographic polarity

March 2, 2016
Author(s)
Matthew D. Brubaker, Alexana Roshko, Paul T. Blanchard, Todd E. Harvey, Norman A. Sanford, Kristine A. Bertness
The polarity of gallium nitride (GaN) nanowire nuclei grown on AlN layers was studied by piezoresponse force microscopy (PFM). N- or Al-polar AlN layers were grown by molecular beam epitaxy (MBE) on Si (111) substrates by use of Al- or N-rich growth

Near-field control and imaging of free charge carrier variations in GaN nanowires

February 15, 2016
Author(s)
Samuel Berweger, Paul T. Blanchard, Matthew Brubaker, Kevin J. Coakley, Norman A. Sanford, Thomas Mitchell (Mitch) Wallis, Kris A. Bertness, Pavel Kabos
Despite their uniform crystallinity, the shape and faceting of semiconducting nanowires (NWs) can give rise to variations in structure and associated electronic properties. Here we investigate local variations in electronic structure across individual n

Polarity-Controlled GaN/AlN Nucleation Layers for Selective-Area Growth of GaN Nanowire Arrays on Si(111) Substrates by Molecular Beam Epitaxy

December 18, 2015
Author(s)
Matthew D. Brubaker, Shannon M. Duff, Todd E. Harvey, Paul T. Blanchard, Alexana Roshko, Aric W. Sanders, Norman A. Sanford, Kristine A. Bertness
We have demonstrated dramatic improvement in the quality of selective-area GaN nanowire growth by controlling the polarity of the underlying nucleation layers. In particular, we find that N- polarity is beneficial for the growth of large ordered nanowire

Periodic dynamics, localization metastability, and elastic interaction of colloidal particles with confining surfaces and helicoidal structure of cholesteric liquid crystals

December 4, 2014
Author(s)
Michael C. Varney, Qiaoxuan Zhang, Mykola Tasinkevych, Nuno M. Silvestre, Kristine A. Bertness, Ivan I. Smalyukh
Although nematic and cholesteric liquid crystals are three-dimensional fluids, they also possess long- range orientational ordering of their constituent molecules, supporting both topological defects and chiral superstructures. Implications of this

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