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Search Publications by: Alexana Roshko (Fed)

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Displaying 76 - 100 of 172

High Degree of Crystalline Perfection in Spontaneously Grown GaN Nanowires

January 1, 2006
Author(s)
Kristine A. Bertness, Alexana Roshko, Albert Davydov, Igor Levin, Mark D. Vaudin, Joy Barker, John B. Schlager, Norman Sanford, Larry Robins
We have grown a variety of isolated GaN nanowires using gas-source molecular beam epitaxy (MBE) and characterized their structural and optical properties. The nanowires have demonstrated a number of promising materials characteristics, including low defect

Spontaneously grown GaN and AlGaN nanowires

January 1, 2006
Author(s)
Kristine A. Bertness, Alexana Roshko, Norman A. Sanford, Joy Barker, Albert Davydov
We have identified crystal growth conditions in gas-source molecular beam epitaxy (MBE) that lead to spontaneous formation of GaN nanowires with high aspect ratio on Si (1 1 1) substrates. The nanowires were oriented along the GaN c-axis and normal to the

GaAs Buffer Layer Morphology and Lateral Distributions of InGaAs Quantum Dots

May 1, 2005
Author(s)
Alexana Roshko, Todd E. Harvey, Susan Y. Lehman, Richard Mirin, Kristine A. Bertness, Brittany Hyland
Atomic force microscopy was used to study the morphology of GaAs buffer layers and the density and height distributions of self-assembled InGaAs quantum dots (QDs) grown on these buffers by molecular beam epitaxy. The surface roughness and terrace size of

Storage Conditions for High-Accuracy Composition Standards of AlGaAs

May 1, 2005
Author(s)
Kristine A. Bertness, Alexana Roshko, S. E. Asher, Craig L. Perkins
AlGaAs epitaxial films were stored under different environmental conditions and the resulting surface oxidation and contamination variations measured using several analytical techniques. Auger depth profiles confirmed that oxidation and carbon

Fabrication and Analysis of GaN Nanorods grown by MBE

January 1, 2005
Author(s)
Norman Sanford, Larry Robins, Matthew H. Gray, J E. Van Nostrand, C Stutz, R Cortez, Albert Davydov, Alexander J. Shapiro, Igor Levin, Alexana Roshko
GaN nanorods were grown on c-plane sapphire substrates under N-rich conditions by plasma-assisted molecular-beam epitaxy. Scanning electron microsopy revealed densely packed nanorods of hexagonal cross section with diameters ranging from roughly 40 to 100

EBSD Measurement of Strains in GaAs due to Oxidation of Buried AlGaAs Layers

February 27, 2004
Author(s)
T Keller, Alexana Roshko, R.H. Geiss, Kristine A. Bertness, T.P. Quinn
We have characterized elastic strain fields associated with the wet-thermal oxidation of buried Al xGa 1-xAs (x 0.98) layers of thickness 80 nm, situated between GaAs layers of thickness 200 nm, on a GaAs substrate. The compressive strains accompanying

Electron Backscatter Diffraction for Studies of Localized Deformation

July 1, 2003
Author(s)
Roy H. Geiss, Alexana Roshko, Kristine A. Bertness, R R. Keller
Electron backscatter diffraction (EBSD) was used to study localized deformation in two types ofconstrained-volume materials. We present a study of deformation in narrow aluminum interconnects afterlow frequency, AC cycling at high current density. Joule

Electron Backscatter Diffraction for Studies of Localized Deformation

March 1, 2003
Author(s)
R.H. Geiss, Alexana Roshko, Kristine A. Bertness, T Keller
Electron backscatter diffraction (EBSD) was used to study localized deformation in two types of constrained-volume materials. We present a study of deformation in narrow aluminum interconnects after low frequency, AC cycling at high current density. Joule

Biaxial Stress Dependence of the GaAs-Like and AlAs-Like Raman Lines in Al x Ga 1-x As

January 1, 2003
Author(s)
Grady S. White, Albert J. Paul, Kristine A. Bertness, Alexana Roshko
Raman peak shifts of Al xGa 1-xAs have been measured as a function of both x and applied biaxial stress in a backscatter geometry. Within the precision of the Raman measurements, the stress-induced peak shifts of the Raman singlet GaAs-like and AlAs-like

Interlaboratory comparison of InGaAsP EX-SITU characterization

January 1, 2003
Author(s)
Alexana Roshko, Kristine A. Bertness
A study to improve the accuracy of ex-situ characterization of InGaAsP materials for optoelectronics is underway. Six InGaAsP thin film specimens, with nominal photoluminescence wavelengths of 1.1, 1.3 and 1.5 mm, have been measured, with X-ray diffraction

Investigation of the Shape of InGaAs/GaAs Quantum Dots

January 1, 2003
Author(s)
Susan Y. Lehman, Alexana Roshko, Richard Mirin, John E. Bonevich
Three samples of self-assembled In 0.44Ga 0.56As quantum dots (QDs) grown on (001) GaAs by molecular beam epitaxy (MBE) were studied using atomic force microscopy (AFM)) and high-resolution transmission electron microscopy (TEM) in order to characterize

X-ray diffraction, photoluminescence and composition standards of compound semiconductors

January 1, 2003
Author(s)
Alexana Roshko, Kristine A. Bertness, J T. Armstrong, Ryna B. Marinenko, Marc L. Salit, Lawrence H. Robins, Albert J. Paul, R J. Matyi
Work is underway to develop composition standards and standardized assessment procedures for compound semiconductors. An AlGaAs composition standard with less than 2% uncertainty is being developed. The improved accuracy of this standard is being achieved