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  • 1
    Electronic Resource
    Electronic Resource
    Site-selective spectroscopy of hydrogenic sites in CaF2:Er3+ crystals (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 521-544 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Laser selective excitation and optical absorption studies of hydrogenated CaF2:0.05% Er3+ crystals have revealed 16 Er3+ ion sites involving H− or D− ion charge compensation. The relative occurrence of these sites can be controlled over a wide range by varying the duration of the hydrogenation treatment. The hydrogenic nature of these sites is established by the observation of local mode absorption lines in the infrared, Er3+ ion electronic line isotope shifts and associated local mode vibronic lines involving the H− and D− ions. Local mode infrared absorption frequencies of four sites are reported for most rare-earth ions. Five new Er3+−F− sites were identified in the laser selective excitation study. For 〈100〉 and 〈111〉 oriented crystals the fluorescence spectra of several of the sites exhibit well-defined polarization which determines their Er3+ ion site symmetries. Symmetry confirmations are also established for the two previously reported single Er3+ ion sites involving fluoride ion compensation. Eleven of the hydrogenic sites reported here are classified into two families, each derived from a single Er3+ ion site of the parent crystal, while three others are attributed to sites of nearly cubic Er3+ ion symmetry. Detailed spectroscopic results for these sites are presented, together with a crystal-field analysis for the C4v symmetry sites and some model assignments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452304
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  • 2
    Electronic Resource
    Electronic Resource
    Computer control and data-acquisition system for the rf test facility (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1904-1906 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The radio frequency test facility (RFTF) at Oak Ridge National Laboratory, used to test and evaluate high-power ion cyclotron resonance heating (ICRH) systems and components, is monitored and controlled by a multicomponent computer system. This data-acquisition and control system consists of three major hardware elements: (1) an Allen-Bradley PLC-3 programmable controller, (2) a VAX 11/780 computer, and (3) a CAMAC serial highway interface. Operating in LOCAL as well as REMOTE mode, the programmable logic controller (PLC) performs all the control functions of the test facility. The VAX computer acts as the operator's interface to the test facility by providing color mimic panel displays and allowing input via a trackball device. The VAX also provides archiving of trend data acquired by the PLC. Communications between the PLC and the VAX are via the CAMAC serial highway. Details of the hardware, software, and the operation of the system are presented in this paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138790
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  • 3
    Electronic Resource
    Electronic Resource
    Apparatus and technique for reconstruction of flaws using model-based elastic wave inverse ultrasonic scattering (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 3089-3098 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An automated multiviewing ultrasonic apparatus and signal processing routine have been developed for utilization in nondestructive evaluation (NDE) of materials. The instrument has been developed to take advantage of recent advances in long and intermediate wavelength inverse scattering of elastic waves, and provides a 3-D reconstruction of a flaw. Although the reconstruction obtained does not contain fine details of the flaw's structure, it provides sufficient information about the flaw (size, orientation, and selected materials properties) so that failure-predictive decisions can be made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139211
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  • 4
    Electronic Resource
    Electronic Resource
    Planar channeling in GaAs/InxGa1−xAs/GaAs strained-layer structures (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1510-1515 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Planar {110} channeling measurements with 1–2-MeV He+ ions have been used to investigate strained-layer structures of (100) GaAs/InxGa1−xAs/GaAs with x=0.07–0.17. Beam-steering effects in the surface GaAs layer are observed to have a major influence on {110} planar angular scans carried out in the InxGa1−xAs layers resulting generally in a double or more complex-shaped angular dip. A simple computer simulation has been developed which determines the main features of the experimental angular scan data. Comparison of simulation and experimental data allows a reasonable determination of the kink angle θK between the {110} planes for the surface GaAs and underlying strained layer. Only in limiting cases is it possible to unequivocally determine θK from the experimental data alone. They are as follows: (i) when θK=0; (ii) θK〉2ψ pc (ψ pc is the critical angle for {110} planar channeling); and (iii) when the thickness t of the top layer is thin (t(very-much-less-than)2d/ψ pc, where d is the {110} interplanar spacing).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342966
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  • 5
    Electronic Resource
    Electronic Resource
    Conversion of the SRS to a higher brilliance lattice (invited) : International conference on synchrotron radiation instrumentation (1989)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 60 (1989), S. 1377-1381 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The SRS at Daresbury has been upgraded by the addition of quadrupoles which reduce the emittance by a factor of 15. In order to do this without disturbing the beamlines, all 16 straight sections were rebuilt. Additional sextupole and octupole magnets were included, as was additional pumping capacity. Completely new beam monitor and vertical steering systems have been incorporated. The SRS was shut down on 1 October 1986 and, after recommissioning, regular scheduled operation for users at the rate of nearly 6000 h per year has been in effect again since June 1987. Scheduled operation is at 2 GeV with the 5T wiggler operational. The gain in brightness is as expected. Maximum beam current at 2 GeV is now 280 mA. Beam lifetime is 20 h at 200 mA. Diffraction patterns of small angle scattering from muscle obtained with an electronic area detector show that with the improved brilliance, diffraction lines corresponding to spacings exceeding 15 000 A(ring) can be clearly resolved. Work is about to start on the provision of a second superconducting wiggler with 6T field feeding five new experimental stations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140996
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  • 6
    Electronic Resource
    Electronic Resource
    Bessel beam ultrasonic transducer: Fabrication method and experimental results (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2066-2068 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report experimental results from a first-of-a-kind ultrasonic transducer that generates a beam with a Bessel function profile. Using a technique of nonuniform poling, an axially symmetric Bessel function pattern is "polarized into'' a piezoelectric ceramic element. The resulting circular-disk transducer has the usual full-plating electrode configuration, but produces an ultrasonic beam with a radial displacement profile approximating that of the Bessel function J0 (r), both in amplitude and in phase. The radiation field of a 1-in.-diam, 2.25 MHz Bessel transducer mapped out with a point probe shows good agreement with calculated results using a Gauss-Hermite model. Bessel transducers are of particular interest in attempts to achieve "diffractionless'' beams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102107
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  • 7
    Electronic Resource
    Electronic Resource
    Highly oriented Tl2Ba2Ca2Cu3O10 thin films by pulsed laser evaporation (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 760-762 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated superconducting thin films on MgO(100) substrates with nearly pure Tl2Ba2Ca2Cu3O10 (2:2:2:3) phase using pulsed laser evaporation and post-annealing. The films had c axes perpendicular to the substrates. Superconducting films with onset temperatures of 125 K and zero resistance at 110 K were obtained. X-ray microprobe fluorescence measurements indicate that a typical composition of films is Tl0.66Ba1.77Ca1.46Cu3Ox, which is low in Tl compared to that expected for the 2:2:2:3 phase. A typical grain size is greater than 10 μm as revealed by scanning electron microscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101473
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  • 8
    Electronic Resource
    Electronic Resource
    Experimental study of implantation-induced disordering in InGaAsP strained multiple-quantum-well heterostructures (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1239-1241 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of strain on F+ and Si+ implantation-induced compositional disordering in InGaAsP strained layer multiple-quantum-well (MQW) heterostructures has been studied by investigating the temperature dependence of the photoluminescence (PL) spectra and spatial distribution of degree of polarization of PL for both compressive and tensile strained, and unstrained MQW heterostructures. It was found that under similar implantation and anneal conditions a spectral blueshift occurs which is largest in the compressively strained structure and the smallest in the tensile one. This behavior is explained in terms of implantation-enhanced interdiffusion, by taking into account the composition differences of elements between the wells and barriers. The development of strain related to the process of interdiffusion has been experimentally observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112082
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  • 9
    Electronic Resource
    Electronic Resource
    Group V incorporation in InGaAsP grown on InP by gas source molecular beam epitaxy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3021-3027 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The incorporation of the group V components in In1−xGaxAsyP1−y, grown lattice matched to InP by gas source molecular beam epitaxy, has been studied over the entire alloy range, 0≤y≤1, as a function of the group V source composition, the V/III beam flux ratio, and the substrate surface orientation. Several aspects of the group V incorporation are most easily understood in terms of a simple model involving a constant incorporation coefficient and an As "underpressure'' condition. An improved description of the results at lower values of the V/III flux ratio is provided by a thermodynamic model based on equilibrium reactions for the formation of the binary constituents, and using the bulk properties of the solid solution. However, the thermodynamic model is quantitatively incorrect for large values of the V/III flux ratio. Furthermore, the results for different surface orientations reveal additional weaknesses in the thermodynamic model and suggest the need to account for the surface bonding configurations in describing the group V incorporation in epitaxial growth. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361241
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  • 10
    Electronic Resource
    Electronic Resource
    Electrical properties of p-type InGaAsP and InGaAs irradiated with He+ and N+ (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5580-5583 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: He+ and N+ ion irradiation of epitaxial p-type In0.76Ga0.24As0.58P0.42 and In0.53Ga0.47As was performed at 300 K to obtain high-resistivity regions. In both the ternary and quaternary samples the resistivity first increases with ion dose. A maximum is reached at a critical dose depending on the ion species and initial doping concentration. Above this dose the conductivity converts to n type and the resistivity steadily decreases to ∼102 Ω cm in InGaAsP and ∼2 Ω cm in InGaAs. After thermal annealing the type converted samples revert to p type. However, for ion doses ≥1013 cm−2 the high resistivities remain stable up to 700 K. The results suggest that simple point defects, rather than complexes are responsible for the changes in the electrical properties of the samples. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359199
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