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  • 1
    Electronic Resource
    Electronic Resource
    Heteroepitaxial wurtzite and zinc-blende structure GaN grown by reactive-ion molecular-beam epitaxy: Growth kinetics, microstructure, and properties (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 189-204 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reactive-ion molecular-beam epitaxy has been used to grow epitaxial hexagonal-structure α-GaN on Al2O3(0001) and Al2O3(011¯2) substrates and metastable zinc-blende-structure β-GaN on MgO(001) under the following conditions: growth temperature Ts=450–800 °C; incident N+2/Ga flux ratio JN+2/JGa=1–5; and N+2 kinetic energy EN+2=35–90 eV. The surface structure of the α-GaN films was (1×1), with an ≈3% contraction in the in-plane lattice constant for films grown on Al2O3(0001), while the β-GaN films exhibited a 90°-rotated two-domain (4×1) reconstruction. Using a combination of in situ reflection high-energy electron diffraction, double-crystal x-ray diffraction, and cross-sectional transmission electron microscopy, the film/substrate epitaxial relationships were determined to be: (0001)GaN(parallel) (0001)Al2O3 with [21¯1¯0]GaN(parallel)[11¯00]Al2O3 and [11¯00]GaN(parallel)[12¯10]Al2O3, (21¯1¯0)GaN(parallel)(011¯2)Al2O3 with [0001]GaN(parallel)[01¯11]Al2O3 and [01¯10]GaN(parallel)[21¯1¯0]Al2O3, and (001)GaN(parallel)(001)MgO with [001]GaN(parallel)[001]MgO.Films with the lowest extended defect number densities (nd(approximately-equal-to)1010 cm−2 threading dislocations with Burgers vector a0/3〈112¯0(approximately-greater-than)) and the smallest x-ray-diffraction ω rocking curve widths (5 min) were obtained using Al2O3(0001) substrates, Ts≥650 °C, JN+2/JGa≥3.5, and EN+2=35 eV. Higher N+2 acceleration energies during deposition resulted in increased residual defect densities. In addition, EN+2 and JN+2/JGa were found to have a strong effect on film growth kinetics through a competition between collisionally induced dissociative chemisorption of N2 and stimulated desorption of Ga as described by a simple kinetic growth model. The room-temperature resistivity of as-deposited GaN films grown at Ts=600–700 °C with EN+2=35 eV increased by seven orders of magnitude, from 10−1 to 106 Ω cm, with an increase in JN+2/JGa from 1.7 to 5.0. Hall measurements on the more conductive samples yielded typical electron carrier concentrations of 2×1018 cm−3 with mobilities of 30–40 cm2 V−1 s−1. The room-temperature optical band gaps of α-GaN and β-GaN were 3.41 and 3.21 eV, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353882
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  • 2
    Electronic Resource
    Electronic Resource
    Defect ordering in epitaxial α-GaN(0001) (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 8195-8197 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The microstructure of nominally undoped epitaxial wurtzite-structure α-GaN films, grown by gas-source molecular-beam epitaxy, plasma-assisted molecular-beam epitaxy, and metalorganic chemical-vapor deposition, has been investigated by transmission electron microscopy (TEM) and high-resolution TEM. The results show that undoped α-GaN films have an ordered point-defect structure. A model of this defect-ordered microstructure, based upon a comparison between experimental results and computer simulations, is proposed. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357873
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  • 3
    Electronic Resource
    Electronic Resource
    How Recognizing “Comorbidities” in Psychopathology May Lead to an Improved Research Nosology (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Clinical psychology 1 (1994), S. 0 
    Details
    ISSN: 1468-2850
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Psychology
    Notes: A short history of the roots of DSM-III and the politics of its creation help to explain the extensive occasions it offers for fulfilling criteria for multiple diagnoses. With use of standardized interviews, it becomes possible to discover all the diagnoses a single person can qualify for. This should prompt rethinking how diagnoses are selected and what rules for preemptions accord with the nature of psychopathology.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1468-2850.1994.tb00010.x
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  • 4
    Electronic Resource
    Electronic Resource
    Crystal growth and electronic properties of ultrahigh vacuum ion-beam sputter deposited Sb-doped Si(001)2×1 (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1398-1400 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality homoepitaxial Sb-doped Si(001)2×1 films have been grown on p-type Si(001) substrates by ultrahigh vacuum ion-beam sputter deposition (IBSD) at temperatures Ts between 450 and 750 °C. The load-locked multichamber system is equipped with in situ reflection high-energy electron diffraction. Sputter deposition was carried out using a 1 keV Kr+ ion beam generated by a modified Kaufman-type ion source with post-extraction electrostatic ion optics. All films were 1 μm thick and deposited at a rate of 0.35 μm h−1. Results of plan-view, cross-sectional, and convergent-beam transmission electron microscopy analyses showed that as-deposited films are highly perfect with no visible defects. Sb incorporation probabilities σSb ranged from (approximately-equal-to)0.1 at Ts=750 °C to (approximately-equal-to)1 for Ts≤550 °C with no indication by secondary-ion mass spectrometry (SIMS) of Sb surface segregation. These σSb values are one to three orders of magnitude larger than for coevaporative Sb doping during molecular beam epitaxy where extensive Sb surface segregation is observed. A comparison of calibrated SIMS and Hall-effect measurements established that the incorporated Sb exhibited complete electrical activity. SIMS analyses also showed no detectable Kr (detection limit (approximately-equal-to)5×1017 cm−3). Temperature-dependent (15–300 K) electron mobilities were equal to the best reported bulk Si values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111895
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  • 5
    Electronic Resource
    Electronic Resource
    Growth of GaN(0001)1×1 on Al2O3(0001) by gas-source molecular beam epitaxy (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 60 (1992), S. 2505-2507 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Gas-source molecular beam epitaxy (GSMBE), utilizing Ga and NH3, has been used to grow single-crystal GaN(0001)1×1 on Al2O3(0001) substrates at temperatures Ts between 700 and 850 °C. In situ reflection high-energy electron diffraction studies show a transition from three-dimensional to two-dimensional growth at Ts(approximately-greater-than)770 °C. For (approximately-equal-to)1-μm-thick GaN layers, the best room-temperature carrier mobilities, 100–110 cm2 V−1 s−1, with carrier concentrations of 1–4×1018 cm−3, were obtained at Ts≥780 °C. These are the highest reported mobilities for MBE GaN. Band-to-band photoluminescence was observed in these films at room temperature. Cross-sectional transmission electron microscopy showed that the primary defects in the films were threading dislocations, with Burgers vectors a0/3〈21¯1¯0〉, and stacking faults.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.106948
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  • 6
    Electronic Resource
    Electronic Resource
    Low-temperature Si(001) epitaxy using low-energy (〈E 〉(approximately-equal-to)18 eV) Si atoms (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 3236-3238 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The use of energetic (average energy (approximately-equal-to)18 eV), rather than thermal ((approximately-equal-to)0.2 eV), Si beams during deposition at R=1 A(ring) s−1 was found to increase the Si(001) epitaxial thickness te (100 A(ring)–1.2 μm) by up to an order of magnitude over the growth temperature range Ts=80–300 °C. The overall increase in te is attributed primarily to a more effective filling of interisland trenches which form during growth in the low adatom mobility two-dimensional multilayer mode and provide preferential sites for the nucleation of the terminal amorphous phase. In addition, the behavior of te(Ts) at constant R and te(R) at constant Ts is quite different than that reported for films grown by molecular-beam epitaxy. A decrease in the slope of ln(te) versus −1/Ts at Ts〈225 °C indicates an additional increase in the epitaxial thickness at very low growth temperatures while at constant Ts, 150 °C, te increases with decreasing R, reaches a maximum, and then decreases. These latter effects are explained in terms of changes in average island sizes giving rise to corresponding changes in interlayer mass transport. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112423
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  • 7
    Electronic Resource
    Electronic Resource
    Deracemization via Highly Enantioselective Enolate Protonation Using a Chiral Aniline as the "Acid" (1994)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 116 (1994), S. 2175-2176 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00084a080
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  • 8
    Electronic Resource
    Electronic Resource
    Vietnam veterans' rapid recovery from heroin addiction: a fluke or normal expectation? (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Addiction 88 (1993), S. 0 
    Details
    ISSN: 1360-0443
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Notes: Between 1972 and 1974, the outcomes of army enlisted men who had served in Vietnam during 1970–71 were evaluated and compared with that of a matched group. This paper reports the major findings of that study with respect to frequency of narcotic addiction in and after Vietnam, and the major risk factors for Vietnam addiction and later relapse. Extraordinary access to records facilitated drawing the sample, locating it, and verifying interview responses. The surprisingly low levels of readdiction and the rarity of addiction to narcotics alone as compared with poly-substance dependence are findings still not entirely incorporated into public and scientific views of heroin addiction. Some defenses against that incorporation are examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1360-0443.1993.tb02123.x
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  • 9
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    Pregnancies, Childrearing, and Mental Health Problems in Adolescents (1990)
    Beverley Hills, Calif. : Periodicals Archive Online (PAO)
    Youth and Society. 21:4 (1990:June) 483 
    Details
    ISSN: 0044-118X
    Topics: Psychology , Sociology
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:c446-1990-021-04-000004
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  • 10
    Electronic Resource
    Electronic Resource
    Conduct Disorder (1991)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of child psychology and psychiatry 32 (1991), S. 0 
    Details
    ISSN: 1469-7610
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine , Psychology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1469-7610.1991.tb00008.x
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