Susan E. Babcock

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The discovery of superconductivity at 39 K in magnesium diboride offers the possibility of a new class of low-cost, high-performance superconducting materials for magnets and electronic applications. This compound has twice the transition temperature of Nb3Sn and four times that of Nb-Ti alloy, and the vital prerequisite of strongly linked current flow has(More)
GaAs-based multiple quantum well (MQW) heterostructures comprised of metastable alloys such as GaAs1 ySby-GaAs1 zNz have potential for realizing high-performance and low temperature-sensitivity lasers in the 1.55 mm wavelength region. However, straininduced ‘lattice-latching’ and Sb-surface segregation effects limit the Sb-mole fractions in the(More)
Grain morphology and crystallographic texture were investigated by electron microscopy in four different polycrystalline forms of superconducting MgB2. The materials included a hot-pressed sintered MgB2 pellet, a pellet reacted in situ from Mg and B, an in situ reacted MgB2 filament and a pulsed-laser-deposited thin film grown on a single crystalline [111](More)
An important predicted, but so far uncharacterized, property of the new superconductor MgB2 is electronic anisotropy arising from its layered crystal structure. Here we report on three c-axis oriented thin films, showing that the upper critical field anisotropy ratio H ‖ c2/H ⊥ c2 is 1.8 to 2.0, the ratio increasing with higher resistivity. Measurements of(More)
We have examined the morphology and composition of embedded nanowires that can be formed during molecular beam epitaxy of GaAs(1-x)Bi(x) using high angle annular dark field ('Z-contrast') imaging in an aberration-corrected scanning transmission electron microscope. Samples were grown in Ga-rich growth conditions on a stationary GaAs substrate. Ga-rich(More)
The Ag/Bi-Sr-Ca-Cu-0 (BSCCO) interface in Ag-clad Bi-2212 tapes was investigated by high-resolution transmission electron microscopy. The interface was found to be well bonded and free of nonsuperconducting second phases. However, a one-half-unit-cell-thick layer of the Bi-2201 phase was observed between the Bi-2212 phase and the Ag-cladding. A very strong(More)
The metal organic vapor-phase epitaxy (MOVPE) growth conditions and properties of fully strained GaAs1 y zSbyNz/InP multiquantum wells (MQWs) are investigated. Higher Sb incorporation within the strained GaAs1 ySby layers was observed when using a higher Sb/(As+Sb) precursor ratio and higher growth temperature. However, lattice-latching effects and the(More)
The effects of thermal annealing on the emission and microstructural characteristics of GaAs0.88Sb0.10N0.02/InP multiple quantum well (QW) structures were studied by photoluminescence (PL) spectroscopy and transmission electron microscopy (TEM). The results show that the optimum annealing conditions lead to improved PL intensity accompanied by only a small(More)
Diffraction-contrast TEM, focused probe electron diffraction, and high-resolution X-ray diffraction were used to characterize the dislocation arrangements in a 16μm thick coalesced GaN film grown by MOVPE LEO. As is commonly observed, the threading dislocations that are duplicated from the template above the window bend toward (0001). At the coalescence(More)
The growth of pseudomorphically strained GaAs1 ySby layers with high Sb-mole fractions of yX0.35 are desired on GaAs substrates for making lasers and detectors in the mid-infrared range. The effect of gas-phase precursor chemistry on the strained-layer Sbincorporation efficiency in metalorganic vapor phase epitaxy (MOVPE) was determined using four(More)