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Search Publications by: Alexana Roshko ()

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Displaying 51 - 75 of 88

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

Ex-situ Characterization of InGaAsP

November 11, 2002
Author(s)
Alexana Roshko, Kristine A. Bertness
An interlaboratory comparison was undertaken to assess differences in X-ray and photoluminescence measurements from different laboratories. Six InGaAsP specimens, with nominal photoluminescence peak wavelengths of 1.1, 1.3 and 1.5 υm, were measured

Formation of InAs/GaAs quantum dots by dewetting during cooling

July 1, 2002
Author(s)
Richard P. Mirin, Alexana Roshko, M. van der Puijl, Andrew G. Norman
We describe a method to form InAs quantum dots on GaAs by cooling an InAs film that is deposited at high substrate temperatures. The reflection high-energy electron diffraction pattern taken after deposition of 1.9 monolayers of InAs on (100) GaAs at 540

InGaAsP Ex-situ characterization

July 1, 2002
Author(s)
Alexana Roshko, Kristine A. Bertness
An interlaboratory comparison has been undertaken of X-ray and photoluminescence measurements of InGaAsP on InP. Six 1 cm 2 specimens are being measured, with nominal photoluminescence wavelengths of 1.1, 1.3 and 1.5 υm (2 of each). Preliminary maps of the

Comparison of AlGaAs oxidation in MBE and MOCVD grown samples

January 1, 2002
Author(s)
Y Chen, Alexana Roshko, Kristine A. Bertness, Dennis W. Readey, Marc A. Mansfield, M. Tan, A. Tandon
Simultaneous wet thermal oxidation of MBE and MOCVD grown Al xGa 1-xAs layers showed that the epitaxial growth method does not influence the oxidation rate. Nearly identical oxidation depths were measured for samples grown by both techniques. It was found

Passive and Active Characterization of Hybrid Glass Substrates for Telecommunication Applications

January 1, 2002
Author(s)
Joseph S. Hayden, Robert D. Simpson, Samuel D. Conzone, Robert K. Hickernell, Berton Callicoatt, Alexana Roshko, Norman Sanford
Phosphate glasses have become increasingly popular for planar waveguide devices owing in part to the development of a number of different commercial compositions with a wide range of optical, physical, chemical and laser properties. In addition, the recent

Hybrid glass substrates for waveguide device manufacture

April 15, 2001
Author(s)
Samuel D. Conzone, Joseph S. Hayden, David S. Funk, Alexana Roshko, D. L. Veasey
Hybrid glass substrates composed of active (ER/Yb co-doped) and passive phosphate glass were prepared by a novel, low temperature joining process. The resulting hybrid substrates are chemically and physically robust; they can be cut, ground and polished by

Evolution of the Shapes of InAs and InGaAs Quantum Dots

January 1, 2001
Author(s)
Richard P. Mirin, Alexana Roshko, M. van der Puijl, Andrew G. Norman
The exact shape of self-assembled quantum dots is still a controversial subject in the literature, despite the fact that this knowledge is of paramount importance for modeling the energy levels and electron wavefunctions in the quantum dots. We will

Optical constants of (Al 0.98 Ga 0.02 ) x O y native oxides

December 14, 1998
Author(s)
K. J. Knopp, Richard Mirin, David H. Christensen, Kristine A. Bertness, Alexana Roshko, R A. Synowicki
We report the optical constants of oxidized crystalline and low-temperature-grown (LTG) Al 0.98Ga 0.02As films, as determined by variable angle spectroscopic ellipsometry. Data were acquired at three angles of incidence over 240-1700nm and fit to a Cauchy

Comparison of heteroepitaxial YBa 2 Cu 3 O 7-d and TiO 2 thin film growth

December 31, 1997
Author(s)
Alexana Roshko, F. J. Stork, David A. Rudman, D. J. Aldrich, P. A. Hotsenpiller
The growth of heteroepitaxial YBa 2Cu 3O 7-δ and TiO 2 thin films has been investigated as a function of deposition rate. film thickness, and deposition temperature. In spite of the fact that the two materials are grown at very different rates and

Imaging of domain-inverted gratings in LiNbO 3 by electrostatic force microscopy

July 7, 1997
Author(s)
H. Bluhm, A. Wadas, R. Wiesendanger, Alexana Roshko, J. A. Aust, Dong-Ha Nam
Ferroelectric domains in LiNbO 3 have been investigated by means of electrostatic force microscopy. Polarization-inverted gratings with 4 υm periodicity were fabricated by titanium diffusion into both + c and - c faces of single-domain LiNbO 3 crystals

Growth morphologies of heteroepitaxial rutile films on sapphire substrates

July 1, 1997
Author(s)
P. A. Morris-Hotsenpiller, Alexana Roshko, J. B. Lowekamp, G. S. Rohrer
The growth morphologies of (1 0 0), (1 0 1) and (0 0 1) rutile films grown on sapphire substrates by the ion-beam sputter deposition technique have been examined as a function of film/substrate orientation, film thickness, substrate surface preparation

Surface resistance and morphology of YBCO films as a function of thickness

June 1, 1997
Author(s)
F. J. Stork, James A. Beall, Alexana Roshko, Donald C. DeGroot, David A. Rudman, Ronald H. Ono, Jerzy Krupka
We have examined the thickness dependence of the growth morphology and surface resistance Rs of laser ablated YBa 2Cu 3O 7-x films with transition temperatures over 89 K and critical current densities greater than 10 6 A/cm2 at 76 K. The thickness was

Passively Q-switched Nd-doped waveguide laser

November 15, 1994
Author(s)
J. A. Aust, K. J. Malone, D. L. Veasey, Norman Sanford, Alexana Roshko
A passively Q-switched waveguide laser operating at 1.054 υm has been demonstrated in a Nd-doped phosphate glass. The channel waveguide was fabricated by K-ion exchange from a nitrate melt. Passively Q-switched pulses were achieved by placement of an