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  • 1
    Electronic Resource
    Electronic Resource
    Epitaxial Y1Ba2Cu3O7 thin films on CeO2 buffer layers on sapphire substrates (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 3986-3988 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pulsed laser deposition has been used to deposit Y1Ba2Cu3O7 layer on CeO2 buffer layers on (11(underbar)02) sapphire. Both layers are epitaxial with the 〈110〉 direction of the CeO2 layer aligned with the 〈2(underbar)021〉 direction of the sapphire substrate. The c-axis Y1Ba2Cu3O7 layer has its 〈100〉 direction alligned with the 〈110〉 direction of the CeO2. Cross-sectional transmission electron microscopy shows the epitaxy to be coherent and the interfaces to be abrupt at an atomic level. The best films have a critical current of 9 × 106 A/cm2 at 4.2 K and lower microwave surface resistance than copper at 77 K and at a frequency of 31 GHz.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349166
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  • 2
    Electronic Resource
    Electronic Resource
    Photodissociation of molecular chlorine in xenon matrices (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2825-2833 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation of Cl2 in crystalline Xe is examined using synchrotron radiation for all state of Cl2 from the C 1Π1u state to the region of Xe exciton absorption. Isolation of atomic chlorine in two dominant trapping sites is observed following photodissociation throughout the spectral region studied. The production efficiency of the thermally stable trapping site was found to increase significantly with temperature and was most pronounced in the region of the onset of the Xe2Cl excitation feature. Correlation between these two processes is explained in terms of a charge-transfer-induced dissociation mechanism involving the formation of a Xe+(Cl2)− intermediate. In contrast to Ar and Kr matrices, photodissociation of Cl2 in Xe appears to occur without a pronounced cage effect. This observation is rationalized in terms of the larger lattice parameters of Xe which allows isolation of Cl2 and Cl at single substitutional and octahedral interstitial sites, respectively. From this structural information, simple models are presented for the production of Cl in the two different kinds of trapping sites. Thus production of the thermally unstable site involves the symmetric dissociation of Cl2 with both Cl atoms occupying octahedral interstitial sites separated by a single lattice constant of Xe. The thermally stable site involves the isolation of one Cl atom at the substitutional site originally occupied by the Cl2 parent molecule and the other at an octahedral interstitial site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461979
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  • 3
    Electronic Resource
    Electronic Resource
    Rydberg series of charge-transfer excitations: Cl and H in rare gas crystals (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1466-1472 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Rydberg series observed in the excitation spectra of Cl and H atoms isolated in the rare gas (Rg) crystals Kr and Xe are associated with the charge transfer species Cl−Rg+ and H−Rg+. The progressions originate from hole states of Rg+ which converge to the top of the rare gas valence band in an analogous manner to the convergence of conventional exciton states to the bottom of the conduction band. A model based on the effective mass approximation and a quantum defect concept predicted such progressions in Xe and Kr crystals and it is supported by the present results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461061
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  • 4
    Electronic Resource
    Electronic Resource
    Spectroscopy and photodissociation of molecular chlorine in argon matrices (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 1039-1045 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A structureless band observed at 180 nm in the absorption and excitation spectra of Cl2/Ar matrices is tentatively assigned as the spin forbidden 3Σ+u ← X 1Σ+g transition of molecular chlorine. Having an absorption cross section of approximately 10−18 cm2 in the solid, a twofold order of magnitude increase in the transition probability is observed relative to the gas phase. Wavelength specific measurements of the photodissociation of molecular chlorine in crystalline argon samples showed that a dominant threshold exists in the 130 nm band at 9.2 eV corresponding to absorption into the bound 1 1Σ+u state. The maximum quantum yield for permanent dissociation in the 130 nm band was found to be 0.3. Luminescence evidence indicates that this dissociation does not involve a charge-transfer mechanism but a crossing from the bound 1 1Σ+u state to a repulsive potential on which an impulsive cage escape occurs. Photoexcitation in the 180 nm band also results in the permanent dissociation of chlorine as well as the molecular A→X emission. The dissociation efficiency of this band was found however to be significantly less than in the 130 nm band and very sample preparation dependent, viz., sample crystallinity. In crystalline samples dissociation efficiencies were typically two orders of magnitude less than in noncrystalline samples. No dissociation occurs following excitation into the lower energy 1Π(1u) band at 300 nm irrespective of sample preparation conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460060
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  • 5
    Electronic Resource
    Electronic Resource
    Interpretation and modeling of buried InAs quantum dots on GaAs and InP substrates (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 1784-1787 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Comparisons of buried InAs/GaAs and InAs/InP quantum dots (QDs) utilizing transmission electron microscopy display interesting parallels and differences between the two systems. The higher 7.2% misfit in the InAs/GaAs system produces small (∼20 nm diameter) QDs with a majority displaying a predominately round shape. The lower 3.2% misfit in the InAs/InP system produces larger QDs (∼35 nm diameter) with the majority also displaying a predominately round shape. In both systems, the size of the QDs can be varied by changes in growth procedures and the largest QDs in any population show evidence of faceting © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1384861
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  • 6
    Electronic Resource
    Electronic Resource
    Spectroscopy and photodissociation of chlorine monomers and clusters in argon matrices (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 155-164 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Steady-state and time-resolved emission spectroscopy of the A–X system of Cl2 is used to distinguish molecular chlorine isolated as monomers and clusters in solid argon samples. The lifetime of the metastable A' 3Π2u state is measured to be an order of magnitude less, when chlorine is present as clusters, than when it is truly isolated. Photodissociation of molecular chlorine clusters was found to be insignificant as monitored by the emission of Ar2Cl at 260 nm. Measurement of the dissociation threshold of molecular chlorine in the 9 eV region as a function of temperature showed little variation. Using spectroscopic data it is concluded that dissociation is occurring by an impulsive mechanism involving curve-crossing from the initially populated Ar+(Cl2)− charge transfer state to repulsive potentials correlating with ground state atomic chlorine and not via a harpooning mechanism. A simple microscopic model, drawn from experimental data and pairwise addition of ArCl potential terms, is constructed to describe the steps involved in this dissociation process in the solid lattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462885
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  • 7
    Electronic Resource
    Electronic Resource
    Determination of the size, shape, and composition of indium-flushed self-assembled quantum dots by transmission electron microscopy (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 2272-2277 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Single and multiple layers of self-assembled InAs quantum dots (QDs) produced by the indium-flush technique have been studied by transmission electron microscopy (TEM) in an effort to develop techniques to reproducibly grow QDs of uniform size and shape. To monitor the changes in QD dimensions, plan-view samples of capped single layers were studied as well as cross-sectional samples of QDs in multiple layers and stacks. The changes in the observed round- and square-shaped QD images under various plan-view TEM imaging conditions, as well as the contrast reversal in the center of QD images viewed in cross-section are modeled using the many-beam Bloch-wave approach, including strain. The sizes and shapes of the QDs are determined through the interpretation of the observed (primarily strain) contrast in plan-view and the observed (primarily atomic number) contrast in cross-sectional TEM. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1287226
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  • 8
    Electronic Resource
    Electronic Resource
    Quantum-well intermixing for optoelectronic integration using high energy ion implantation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3697-3705 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The technique of ion-induced quantum-well (QW) intermixing using broad area, high energy (2–8 MeV As4+) ion implantation has been studied in a graded-index separate confinement heterostructure InGaAs/GaAs QW laser. This approach offers the prospect of a powerful and relatively simple fabrication technique for integrating optoelectronic devices. Parameters controlling the ion-induced QW intermixing, such as ion doses, fluxes, and energies, post-implantation annealing time, and temperature are investigated and optimized using optical characterization techniques such as photoluminescence, photoluminescence excitation, and absorption spectroscopy. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359948
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  • 9
    Electronic Resource
    Electronic Resource
    Physical and electrical investigation of ohmic contacts to AlGaAs/GaAs heterostructures (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7966-7972 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanism by which Ni-Au-Ge metallizations establish electrical contact to the two-dimensional electron gas (2DEG) in modulation-doped AlGaAs/GaAs heterostructures is investigated. Transmission electron microscopy was used to examine samples after electrical characterization by magnetoresistance measurements at cryogenic temperatures. We present a picture in which a 2DEG of reduced electron density exists under the deposited metallization. The success of the contacting procedure is described in terms of the magnitude of this density and the size, areal density, and penetration depth of a series of metallic spikes which establish the electrical link to the 2DEG. We suggest that the electrical behavior is not dominated by the current injection process at the spike/2DEG interface but is instead dictated by scattering from the array of antidots formed by the spikes and by a dependence of the 2DEG density on the size of the metallic pad. The implications of this picture for future nanostructure devices, featuring patterned ohmic metallization smaller than a micron, are discussed and preliminary results are reported. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357908
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  • 10
    Electronic Resource
    Electronic Resource
    Electrodeposition and characterization of magnetic Ni-Fe thin films on InP(100) surfaces (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 5795-5799 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electrodeposited magnetic Ni-Fe films are used in storage devices and are applicable as magnetic sensors. In this work, we demonstrate the electrochemical conditions for deposition of permalloy Ni-Fe nanocrystalline films onto InP(100) surfaces. The prepared Ni-Fe films were analyzed by scanning electron microscopy to determine surface morphology and by Auger electron spectroscopy for compositional depth profiling. Permalloy films with bulk composition of 81% Ni and 18% Fe were obtained by electrodeposition at −1.2 V (versus standard calomel electrode) in a bath of 0.5 M NiSO4, 0.02 M FeSO4, 0.4 M H3BO3, pH=3. Transmission electron microscopy measurements show that these films consist of fcc Ni-Fe nanocrystallites embedded in an amorphous matrix. The films also show good magnetic hysteresis loops, with low coercivity. The magnetic properties of these films are improved by an extended anneal at 100 °C. Interdiffusion occurred between Ni-Fe and the InP substrate after the sample was heated to 300 °C, and consequently a loss of ferromagnetic behavior was observed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359643
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