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  • American Institute of Physics (AIP)  (329)
  • American Geophysical Union (AGU)
  • 1995-1999  (329)
  • 1
    Electronic Resource
    Electronic Resource
    Photovoltaic effects in porphyrin polymer films and heterojunctions (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3381-3389 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electropolymerized porphyrin films on indium–tin–oxide substrates have been characterized using Rutherford backscattering spectrometry, absorption spectroscopy, electrical characterization methods and with step profiling. With these methods the density of the films (ρ=1.35 g/cm3) and the absorption coefficients α(λ) have been determined. For film thicknesses exceeding 40 nm, silver electrical contacts without shunts are achieved by evaporation. The dark conductivity of the films amounts to 10−13–10−12 Ω−1 cm−1. When applying a band model for the conduction in the films, the dark space charge limited current and the exponent in the relation between photoconductivity and illumination intensity (σ∼Iγ, γ=0.65±0.05) indicate an exponential trap distribution in the band gap of the films. From the action spectra, filter effects of the photoconductance and low mobilities are inferred. Spin coating of acceptor layers on top of the polymer films results in the formation of heterojunctions showing photovoltaic behavior, with an open-circuit voltage 0.4–0.6 V. The short-circuit current is controlled by electron transfer at the donor/acceptor interface only and is limited by filter effects in the bulk and by the low conductivity of the materials. The optoelectrical properties of the layers are different if analyzed using a mercury contact (higher dark conductivity, no photoconductivity) which is attributed to the intro- duction of dopants from ambient air in this case. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363203
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  • 2
    Electronic Resource
    Electronic Resource
    Highly reflective, long wavelength AlAsSb/GaAsSb distributed Bragg reflector grown by molecular beam epitaxy on InP substrates (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 66 (1995), S. 329-331 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Surface normal optoelectronic devices operating at long wavelengths ((approximately-greater-than)1.3 μm), require distributed Bragg reflectors (DBRs) with a practical number (≤50) of mirror layers. This requirement implies a large refractive index difference between the mirror layers, which is difficult to achieve in the traditionally used phosphide compounds. We demonstrate a highly reflective AlAsSb/GaAsSb DBR grown nominally lattice matched to an InP substrate by molecular beam epitaxy. Reflectivity measurements indicate a stop band centered at 1.74 μm with maximum reflectivity exceeding 98%, which is well fitted by our theoretical predictions. Atomic force microscopy and transmission electron microscopy indicate reasonable crystal quality with some defects due to an unintentional lattice mismatch to the substrate. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114202
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  • 3
    Electronic Resource
    Electronic Resource
    The 2 3Πg and 3 3Πg states of 7Li2: Optical–optical double resonance spectroscopy and ab initio calculations (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5898-5903 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The (2p+2p) 2 3Πg and (2s+3p) 3 3Πg states of 7Li2 have been studied both experimentally and theoretically. Vibrational levels v=0–41 of the 2 3Πg state and v=6–10 of the 3 3Πg state have been observed by perturbation facilitated optical–optical double resonance (PFOODR) spectroscopy. Our ab initio calculations show that the 2 3Πg state, although dissociating into 2p+2p atomic limit, is a Rydberg state and strongly mixed with the (2s+3p) 3 3Πg and (2s+3d) 4 3Πg Rydberg states. Our theoretical calculations show good agreement with our experimental results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470469
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  • 4
    Electronic Resource
    Electronic Resource
    Development of the laser evaporation ion source for lithium beam generation on the Particle Beam Fusion Accelerator (PBFA-II) (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3697-3716 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Laser Evaporation Ion Source (LEVIS) active lithium ion source has been developed for use on the focusing ion diode operated on the 10 TW Particle Beam Fusion Accelerator-II (PBFA-II) [J. P. VanDevender and D. L. Cook, Science 232, 831 (1986)] at Sandia National Laboratories. The source configuration consists of two laser pulses impinging on a heated (200 °C) thin-film LiAg layer on the anode surface. A short-pulse Nd:YAG laser creates a high-density vapor, which is then ionized by a long-pulse dye laser using the LIBORS (laser ionization based on resonant saturation) ionization method. Small-scale experiments determined that this dual laser-based approach can produce a source plasma of adequate density and confinement for acceleration and transport. Hardware modifications were undertaken to correct problems of premature impedance collapse and lack of beam lithium seen on previous PBFA-II experiments. As much as 85 kJ of Li is measured at the beam focus, but the source may not have been operating in a fully active (i.e., preformed) manner. Focusing performance appears superior to a passive LiF ion source operated on PBFA-II with the same magnetic field topology. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873629
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  • 5
    Electronic Resource
    Electronic Resource
    A large-area plasma source excited by a tunable surface wave cavity (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2331-2337 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A large-area high-density microwave plasma is successfully generated at low pressure by a tunable surface wave cavity which consists of a 12 period vane-type slow wave structure. This cavity is operated in the π mode and resonant at 2.45 GHz. The plasma area is in excess of 50 cm×25 cm with a uniformity of ±10% at pressures less than 30 mTorr. A plasma surface wave has been excited so that a plasma density as high as 1.0×1012 cm−3 can be achieved at 30 mTorr for a microwave power of 2.0 kW. The plasma temperature is ∼1.5 eV and the plasma potential is ∼12 V. Above all, the number of the periods of the π-mode cavity can be increased without changing the resonance frequency and the distribution of the microwave fields such that this plasma source is easy to up-scaled. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149759
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  • 6
    Electronic Resource
    Electronic Resource
    ac ohm meter for low-temperature thermometry (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2365-2371 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A high accuracy, low excitation ohm meter optimized for cryogenic thermometry is described. While the instrument simply measures the ac voltage induced across a resistance thermometer for a fixed applied current, a number of design innovations were necessary in order to maintain a high signal-to-noise ratio and absolute accuracy of greater than 10−4 with excitation voltages as low as 50 μV. Among these are a very high stability ac oscillator, a precision current source both stable and accurate with large capacitance loads, and an amplitude locked feedback loop to permit effective filtering of low level 60 Hz pickup. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149764
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  • 7
    Electronic Resource
    Electronic Resource
    Measurement of the permeability of thin films (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 2072-2073 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A system has been developed to directly measure the flow of inert gases through an arbitrary thin film. The system employs a porous aluminum silicate ceramic as the substrate for film deposition, a flow control apparatus to hold the substrate under vacuum and allow a helium gas pressure differential to be established across the substrate, and a helium leak detector to measure the flow of helium through the substrate/film combination. This allows calculation of the permeability of the film. The permeability of plasma enhanced chemical vapor deposited diamondlike carbon films and sputter deposited silicon nitride, and nickel films were measured. A thermally grown silicon dioxide film was also tested. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149714
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  • 8
    Electronic Resource
    Electronic Resource
    Wannier–Stark localization in a strained-layer InxGa1−xAs/InyGa1−yP superlattice (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7161-7163 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present an observation of the Wannier–Stark effect in a strained InGaAs/InGaP superlattice grown on a GaAs substrate. A blueshift of the effective absorption edge is observed in room and low-temperature photocurrent and transmission measurements. A ∼2000 cm−1 absorption change due to the transition of the absorption edge from a broad to a sharp quantum well-like excitonic shape was obtained for as little as a 2 V change in bias voltage. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361487
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  • 9
    Electronic Resource
    Electronic Resource
    Detailed analysis of room-temperature photoreflectance of strained InxGa1−xAs/AlyGa1−yAs undoped single quantum wells (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 4338-4347 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report a detailed analysis of room-temperature photoreflectance data of four InxGa1−xAs/AlyGa1−yAs undoped strained single quantum wells with x≈0.20 and y≈0, 0.05, 0.10, and 0.20. We have compared our results with theoretical calculations based on an effective mass formalism, where possible variations of well and barrier composition and thickness have been included. For all the samples studied we have identified both allowed and forbidden transitions in the spectra and obtain good fits assuming a conduction-band offset Qc of 60%±5%. This detailed analysis shows for the first time that room-temperature photoreflectance measurements alone can be used to determine the well composition and thickness together with the barrier composition and the barrier offset. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361743
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetism in URhSi : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5221-5223 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Our neutron-powder-diffraction experiment revealed that URhSi crystallizes in the orthorhombic TiNiSi (space group Pnma) structure and orders ferromagnetically at low temperatures with the U magnetic moments of 0.11 μB aligned along the c axis. Anomalies in the temperature dependence of the magnetic susceptibility, specific heat and electrical resistivity indicate that URhSi orders below 9.5 K. The enhanced Cp/T value (extrapolated to 0 K) of 186 mJ/mol K2 can be partially reduced in magnetic fields, which indicates a considerable magnetic contribution even at very low temperatures. The ferromagnetic ground state is documented also by magnetization measurements at low temperatures. The high-field magnetization data obtained on oriented powder reveal a strong magnetocrystalline anisotropy. All the results obtained on polycrystalline samples classify URhSi as an itinerant 5f ferromagnet with very reduced U magnetic moments. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361347
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