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  • 1
    Electronic Resource
    Electronic Resource
    Free excitonic transitions in GaN, grown by metal-organic chemical-vapor deposition (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 7001-7004 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamic processes of the free excitonic transitions in GaN grown by metal-organic chemical-vapor deposition (MOCVD) have been studied. The recombination lifetimes of the A and B excitons have been measured at different temperatures and excitation intensities, from which radiative recombination lifetimes of about 0.35 and 0.3 ns for the A and B excitons, respectively, have been obtained. An increase in excitation power has resulted in a drastic enhancement in the radiative decay rate as well as in the exciton photoluminescence quantum yield, suggesting the excitonic transitions may provide gain for laser actions in GaN. The high quality as well as high purity of the investigated MOCVD sample has been demonstrated by the observations of (1) the free A- and B-excitonic transitions, (2) excited states of the free excitons, (3) narrow free excitonic emission linewidths (1.7 meV at 10 K), (4) low electron concentration, and (5) high electron mobilities (∼600 cm2/V s). © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362448
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  • 2
    Electronic Resource
    Electronic Resource
    An HREELS study of π* and σ* negative ion resonances of c(8×2) benzoate on Cu(110) (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 5942-5947 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: For the c(8×2) benzoate on Cu(110) system, multiple unoccupied states have been measured through negative ion resonances by high-resolution electron-energy-loss spectroscopy (HREELS). Based on the azimuthal and polar angle dependences, we assign contributions from B2 and A1 states to a resonant feature in the 〈001〉 direction and contributions from B1 and A1 states in the 〈110〉 direction. The B2 state is observed close to 4.7 eV and the B1 feature is centered at 6.5 eV. The angular and azimuthal dependence of the C–H stretch intensity in HREELS at resonance is consistent with their assignment and the results of ab initio calculations. Overtone intensity shows an exponential decay as a function of overtone quantum number. From the overtone frequencies, an anharmonicity of 0.0272 is obtained which leads to a dissociation energy of the C–H bond of about 81 kcal/mol. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476005
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  • 3
    Electronic Resource
    Electronic Resource
    Vacuum arc plasma transport through a magnetic duct with a biased electrode at the outer wall (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 3329-3331 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Metal plasma formed by a vacuum arc plasma source can be passed through a toroidal-section magnetic duct for the filtering of macroparticles from the plasma stream. In order to maximize the plasma transport efficiency of the filter the duct wall should be biased, typically to a positive voltage of about 10–20 V. In some cases it is not convenient to bias the duct, for example if the duct wall is part of the grounded vacuum system. However, a positively biased electrode inserted into the duct along its outer major circumference can serve a similar purpose. In this article, we describe our results confirming and quantifying this effect. We also show the parametric dependence of the duct transport on the experimental variables. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149913
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  • 4
    Electronic Resource
    Electronic Resource
    The effect of the coupling agent on the packing density and corrosion behavior of NdFeB and SmCo bonded magnets (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5684-5686 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of the coupling agent addition on the specific density and corrosion behavior of NdFeB and SmCo bonded magnets have been investigated. The application of LICA44, a titanate coupling agent, improved the filled volume of the epoxy-based bonded magnets, especially at high compression pressures. When molded at 10.5 T/cm2, specific densities of 6.2 and 6.5 g/cm3 have been obtained for the NdFeB and SmCo bonded magnets, respectively. Incorporating a coupling agent was found to eliminate visible cracks on the SmCo bonded magnets, possibly due to the improvements in the wettability and compatibility of the system. The percentage of the filled volume was increased by 2%–7%. Incorporating LICA44 also improved corrosion resistance of the bonded magnets. For NdFeB, LICA44 reduced the steady state corrosion current Icorr from 69 to 38 μA/cm2. No significant changes in the Icorr were observed for SmCo due to the stable nature of SmCo. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369840
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  • 5
    Electronic Resource
    Electronic Resource
    Temperature-mediated phase selection during growth of GaN on (111)A and (1¯1¯1¯)B GaAs substrates (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 3759-3761 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: GaN layers having the zinc blende and wurtzite structures can be selectively deposited on (111)A and (1¯1¯1¯)B GaAs substrates by varying the growth temperature. Using the growth temperature as a variable, layers having the two structures have been sequentially deposited. The as-grown structures have been examined by cross-sectional high resolution electron microscopy. Results indicate that the two phases once formed are structurally stable in the temperature range examined. Furthermore, the transition from GaN (zinc blende) to GaN (wurtzite) is sharp, whereas a faulted region is observed during the reverse transition. Arguments have been developed to rationalize these observations. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115374
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  • 6
    Electronic Resource
    Electronic Resource
    A study on the exchange coupling of NdFeB-type nanocomposites using Henkel plots (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5917-5919 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The phase transformation and magnetic properties of (Nd0.95La0.05)9.5FebalCo5Nb2B10.5 nanocomposite have been investigated systematically via thermomagnetic analysis, vibration sample magnetometer, x-ray diffraction, and conventional transmission electron microscopy. The Henkel plot was employed to quantify the strength of the exchange coupling between the hard and soft magnetic phases in the as-spun and the thermally treated samples. It was found that remanence Br, coercivity Hci, and maximum energy product BHmax obtained were affected by the magnetic phases present as well as the grain size of constituent phases and their distribution. The Henkel plot successfully interpreted the effect of the exchange coupling on Br, Hci, and BHmax obtained for samples treated below 750 °C. However, it became inadequate for samples treated above 750 °C. Although similar shapes of ΔM–H curves were obtained in the Henkel plot, severe degradation in Br, Hci, and BHmax was found when the thermal treatment temperature was increased from 750 to 850 °C. This degradation may be attributed to the grain growth of the main phases, from 45 to 68 nm, and the development of precipitates. In conjunction with the mass balance, the precipitated phases (presumably borides) may explain the increase in the Tc of Nd2(FeCo)14B and the decreased amount of α-Fe and Fe3B with increasing thermal processing temperature. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369913
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  • 7
    Electronic Resource
    Electronic Resource
    Magnetic coupling in boron-rich NeFeB nanocomposites (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5920-5922 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article, we report types of magnetic domain patterns caused by either dipolar coupling or exchange coupling inside a heat-treated boron-rich NdFeB melt-spun ribbon. The average grain size of the sample was about 38 nm. Single particle domains were commonly observed in Fresnel images all through the specimen, suggesting little exchange coupling among the grains in these regions. Snake-shaped long interactive domains consisting of chains of grains were found in many Foucault images at the regions where exchange coupling is weak. These domains are caused by dipolar coupling along the chains. Wider domains consisting of many grains were also observed by Fresnel images, although they were much less common than the single particle domains. The grains inside a wider domain are believed to be exchange coupled with each other. The magnetic properties of such boron-rich NdFeB composites are influenced more by the dipolar coupling than by exchange coupling between the nanocrystalline grains. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369914
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  • 8
    Electronic Resource
    Electronic Resource
    Super ESCA: First beamline operating at ELETTRA : Proceedings of the 5th international conference on synchrotron radiation instrumentation (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 1618-1620 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The Super-ESCA beamline has been designed for high resolution core level spectroscopy of adsorbates on single crystal surfaces using soft x-ray synchrotron radiation. It receives the light from an 81 period undulator with 5.6 cm period and 4.5 m length in the storage ring ELETTRA. The tunability of this insertion device, at a storage ring electron energy of 2.0 GeV and the connected modified SX700 monochromator allows the performance of experiments at this beamline in the photon energy range 100–2000 eV. This beamline is now operational and first absorption spectra are presented which show available resolving powers varying from 8000 to 3000 for photon energies between 240 and 850 eV. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145862
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  • 9
    Electronic Resource
    Electronic Resource
    The breakdown of asymptotic hydrodynamic models of liquid spreading at increasing capillary number (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 2631-2639 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Complex hydrodynamics near the moving contact line control spreading of a fluid across a solid surface. In the confined region near the contact line, velocity gradients in the fluid are large and viscous forces control the shape of the fluid/fluid interface. The present model for liquid spreading describes the viscous effect on the dynamic interface shape to lowest order in capillary number, Ca. Using videomicroscopy and image analysis techniques, we have examined the shape of liquid/air interfaces very near moving contact lines for Ca≥0.10 where the interfaces are in capillary depression. We find that the theory correctly describes the data up to Ca=0.10 for distances from 20 to 400 μm from the contact line. As Ca increases, the model fails to describe the data in a region near the contact line, which grows as Ca increases. In this expanding region, the model predicts too large a curvature for the interface. We explore the origins of this breakdown by examining the fundamental assumptions of the model. The geometry-dependent part of the solution to O(1) in Ca is sufficient even at Ca=0.44. The breakdown of the model arises from the low order of the geometry-free part of the perturbation solution and/or contributions to the interface shape from the unique hydrodynamics very near the moving contact line. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868711
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  • 10
    Electronic Resource
    Electronic Resource
    Scattered refractive index profiles of thin silicon oxide film on silicon substrate (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 5868-5870 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Randomly scattered depth profiles of refractive index are experimentally observed on thin silicon dioxide films on silicon substrates by means of conventional ellipsometry and gradually chemical etching. Computer simulations with an abrupt model and random uncertainties in ellipsometric angles Ψ and Δ show very similar behavior as experiments, and the distribution of the measured profile in the near interface region is in good agreement with 0.02° standard deviation in Ψ. Simulations also indicate that even very small errors in Ψ, as small as 0.001°, can result in divergent depth profile of the refractive index in the near interface region. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.366404
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