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  • 1
    Electronic Resource
    Electronic Resource
    Effects of substrate temperature on chemical structure of amorphous carbon films (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 2243-2248 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous carbon thin films were prepared at 30, 200, and 450 °C by magnetron sputtering of a graphite target. The surface structure and chemical bonding (sp2/sp3) of the carbon films were characterized by scanning tunneling microscopy (STM) and Raman spectroscopy. STM images show that graphite microcrystallites of 20–40 A(ring) in size are present at the surfaces of all the films and the number of the microcrystallites increases with increasing substrate temperature. The microcrystallites often contain structural defects. Raman measurements show that increasing the substrate temperature results in an increase in the sp2-bonded fraction of carbon atoms and a decrease in the microstructural defects. These results indicate that the microstructural changes are correlated with changes in the chemical bonding ratio (sp3/sp3) and no diamond microcrystallites are present in the amorphous carbon. A three-dimensional atomic structure of the graphite microcrystallites is discussed in terms of turbostratic graphite.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351122
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  • 2
    Electronic Resource
    Electronic Resource
    Efficient time integration of a viscoplastic model for shock waves (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 1356-1358 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An unconditionally stable numerical procedure is developed to integrate the stiff differential equation associated with the flow rule for viscoplasticity used by Swegle and Grady [J. Appl. Phys. 58, 692 (1985)] to predict shock structure. Following the work of Rubin [J. Appl. Math. Phys. ZAMP 40, 846 (1989)] the flow rule is integrated implicitly and is converted into a scalar equation. It is shown that for the Swegle–Grady model this scalar equation reduces to a quadratic equation that can be solved without iteration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346682
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of viscoplasticity in 6061-T6 aluminum (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4523-4530 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results from a previous analysis of experimental data on 6061-T6 aluminum have been used to determine values for material parameters in constitutive equations for viscoplasticity and hardening. In contrast to previous work, the present model includes the continued hardening observed in Hopkinson bar tension experiments and predicts the wave structure measured in plate impact experiments reasonably well. An interesting conclusion of the present work is that the structure of the unsteady portions of weak shocks measured in plate impact experiments can provide a sensitive measure of hardening near the onset of plasticity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.346157
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  • 4
    Electronic Resource
    Electronic Resource
    Modeling of hardening at very high strain rates (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 2742-2747 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A modification of the Bodner–Partom elastic-viscoplastic constitutive model is proposed to account for strain rate dependence of the evolution of hardening. The suggested procedure is for the rate of hardening in the hardening evolution equation to be a direct function of total strain rate. Material constants are determined for oxygen-free-electronic copper and simulations of response behavior at very high rates of straining appear to be consistent with test observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357578
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  • 5
    Electronic Resource
    Electronic Resource
    Homoepitaxial growth of GaN using molecular beam epitaxy (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2195-2198 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, experimental results are presented for the homoepitaxial deposition of a GaN overlayer onto a bulk single-crystal GaN substrate using molecular beam epitaxy. Transmission electron microscopy shows a superior structural quality of the deposited GaN overlayer when compared to heteroepitaxially grown layers. Photoluminescence shows narrow excitonic emission (3.467 eV) and the very weak yellow luminescence, whereas the bulk substrate luminescence is dominated by this deep level emission. These results show that homoepitaxy of GaN can be used to establish benchmark values for the optoelectronic properties of GaN thin films. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363112
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  • 6
    Electronic Resource
    Electronic Resource
    Continuum model of dispersion caused by an inherent material characteristic length (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 4054-4063 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Modifications of the Helmholtz free energy and the stress associated with general constitutive equations of a simple continuum are proposed to model dispersive effects of an inherent material characteristic length. These modifications do not alter the usual restrictions on the unmodified constitutive equations imposed by the first and second laws of thermodynamics. The special case of a thermoelastic compressible Newtonian viscous fluid is considered with attention focused on uniaxial strain. Within this context, the linearized problems of wave propagation in an infinite media and free vibrations of a finite column are considered for the simple case of elastic response. It is shown that the proposed model predicts the dispersive effects observed in wave propagation through a chain of springs and masses as the wavelength decreases. Also, the nonlinear problems of steady wave propagation of a soliton in the absence of viscosity and of a shock wave in the presence of viscosity are discussed. In particular it is shown that the presence of the dispersive terms can cause the stress in a shock wave to overshoot the Hugoniot stress by as much as 50%. This phenomenon may cause an underprediction of the threshold level for failure determined by analysis of stress in shock experiments. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359488
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  • 7
    Electronic Resource
    Electronic Resource
    Refractive index changes of Pd-coated magnesium lanthanide switchable mirrors upon hydrogen insertion (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 408-413 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical effect upon insertion of hydrogen into Pd-coated magnesium lanthanide switchable mirrors is investigated in terms of the changes of their complex refractive indices. A significant change in the optical constants of LnMg layers is seen between the as-deposited state and the dehydrided state after one cycle. Furthermore, the optical effect of switching the Pd cap layer to a PdH cap layer was determined. It is shown that the Pd layer mainly limits the visible transmittance of the hydrided stack to about 35%–40%. Whereas the extinction coefficient of dehydrided LnMg layers at 550 nm is between 2.2 and 3.1, it is as low as 10−4 in the transparent state. This is of great promise to applications requiring large optical contrast (e.g., optical switches). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369399
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  • 8
    Electronic Resource
    Electronic Resource
    Hollow-anode plasma source for molecular beam epitaxy of gallium nitride : Proceedings of the 6th international conference on ion sources (1996)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 905-907 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: GaN films have been grown by molecular beam epitaxy (MBE) using a hollow-anode nitrogen plasma source. The source was developed to minimize defect formation as a result of contamination and ion damage. The hollow-anode discharge is a special form of glow discharge with very small anode area. A positive anode voltage drop of 30–40 V and an increased anode sheath thickness leads to ignition of a relatively dense plasma in front of the anode hole. Driven by the pressure gradient, the "anode'' plasma forms a bright plasma jet streaming with supersonic velocity towards the substrate. Films of GaN have been grown on (0001) SiC and (0001) Al2O3 at 600–800 °C. The films were investigated by photoluminescence, cathodoluminescence, x-ray diffraction, Rutherford backscattering, and particle-induced x-ray emission. The film with the highest structural quality had a rocking curve width of 5 arcmin, the lowest reported value for MBE growth to date. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146834
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  • 9
    Electronic Resource
    Electronic Resource
    Erratum: "Thermodynamic and kinetic processes involved in the growth of epitaxial GaN thin films'' [Appl. Phys. Lett. 62, 1242 (1993)] (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 424-424 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110818
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  • 10
    Electronic Resource
    Electronic Resource
    1.54-μm photoluminescence from Er-implanted GaN and AlN (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 992-994 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the observation of the 1.54-μm luminescence of optically excited Er3+ in ion-implanted epitaxially grown GaN and AlN films using below band-gap excitation. The Er-implanted layers were co-implanted with oxygen. At room temperature, this luminescence for GaN grown on sapphire is nearly as intense as it is at 6 or 77 K and exhibits many resolved transitions between crystal-field levels of the 4I13/2 first excited multiplet and the 4I15/2 ground multiplet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112172
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