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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 3068-3073 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new transmission grating spectrograph for soft x-ray measurement in pulsed plasmas was designed and studied. The spectrograph has an adjustment system with three degrees of freedom, together with an electronic-controlled camera. This design makes it easy to align and use for laser-produced plasmas or the plasma focus. The spectrograph provides spatially resolved spectrum in two dimensions and has a wavelength range of 0.3–30 nm. A transmission grating was used to obtain spatially resolved spectra from plasmas produced by laser-irradiated solid target and gas filled plasma focus. Such a spectrograph is suitable for coupling with a soft x-ray streak camera or a soft x-ray charge coupled device detector for time-resolved studies. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 6041-6051 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An analytic model and molecular dynamics (MD) simulations are used to describe the collisional energy transport and sputtering initiated by a 1–4 eV atom or molecule in low temperature, solid Ar, O2, and N2. In these systems energetic exothermic processes, such as repulsive relaxation events following electronic excitation by a fast ion, an electron or an ultra violet photon, can give kinetic energy to an atom or molecule initiating a sequence of low energy collisions, a minicascade. When such an event occurs near the surface in a low-temperature, condensed-gas solid, atomic or molecular ejection can result. Using MD calculations the moving particles are tracked and the energy and angular spectra of the ejected particles determined. For a distribution of excitations which is uniform with depth, the average number of particles ejected is shown to be proportional to the average initial kinetic energy divided by the sublimation energy. The proportionality constant is only weakly dependent on the condensed-gas solid, since, for the molecular solids studied, the amount of the initial energy transferred into vibrational excitation of the ejecta is small. Therefore, measured electronic-sputtering yields provide an estimate of the energy release in energetic, nonradiative relaxation events. The ejecta exhibit a nearly E−2 kinetic energy spectra for recoil energies, E, much greater than the sublimation energy. The MD calculation of the yields and of the ejecta energy and angular distributions are interpreted here using an analytic model of a cascade of collisions in which the collisions in the solid are not assumed to be binary. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An 8.5 cm multipole ion source for an MM-2U neutral beam injector has been developed. The source is operated with a discharge current of more than 200 A. The saturation ion current at the plasma grid is 300 mA/cm2. A hydrogen ion current of 9 A has been obtained at an accel. voltage of 25 kV with 50 ms pulse duration. This article describes the experiment apparatus and the experimental results.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 887-888 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Metal-semiconductor-metal photodetectors with 100-nm finger spacing and width on a silicon-on-insulator substrate that has a scaled active layer were fabricated and characterized using electro-optic sampling. The unique device structure cuts off carriers generated deep inside the semiconductor substrate, resulting in a measured response time of 3.2 ps and a bandwidth of 140 GHz. Furthermore, the detector structure makes the detector's speed independent of the light penetration depth and thus the light wavelength. Good metal-semiconductor Schottky contact and low detector dark current have been achieved.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 3256-3258 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A dual beam thermal wave probe has been used to measure the thickness of opaque thin films in a noncontact, nondestructive manner. The method relies on the measurement of the differential phase of two interferometrically determined photodisplacement signals. The technique does not require calibration against standard samples and can be used to determine film thicknesses from a few tens of nanometers up to several micrometers. Alternatively, if the film thickness is known, thermal material properties like diffusivity or conductivity can be determined. The conditions under which the system is expected to give the most accurate results are analyzed.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2507-2509 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ultrafast characteristics of crystalline-silicon metal-semiconductor-metal (MSM) photodiodes with 300 nm finger width and spacing were measured with a subpicosecond electro-optic sampling system. Electrical responses with full width at half maximum as short as 5.5 and 11 ps, at corresponding 3 dB bandwidths of 75 and 38 GHz, were generated by violet and red photons, respectively. The difference is attributed to the photon penetration depth which is much larger than the diode finger spacing at red, but smaller at violet. Light-intensity dependence was also examined at different wavelengths, indicating a linear relation and a higher sensitivity in the violet. These results not only demonstrated the fastest silicon photodetector reported to date, but also pinpointed the dominant speed-limiting factor of silicon MSM photodiodes. A configuration is suggested to improve the speed of these detectors at long wavelengths.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The incorporation of the InAs layer as the blocking layer into the GaSb side of the GaSb/AlSb/InAs single-barrier interband tunneling structure resulting in a GaSb/InAs/GaSb/AlSb/InAs resonant interband tunneling structure has been proven to greatly enhance negative differential resistance peak-to-valley current ratios and peak current density. The role of the InAs layer induced electron and light hole coupling related to the device performance is then investigated. A three-band model, incorporating the coupling effect of the spin-orbit split-off hole band, is employed to probe the effect of the InAs layer thickness on the peak current densities and the subband properties of the GaSb/InAs/GaSb/AlSb/InAs resonant interband tunneling structures. The calculated peak current densities are in reasonable agreement with the experimental data reported previously. The transmission coefficients based on the three-band calculation can be used to interpret the variations of the peak current densities well. In addition, the "repulsion'' of the conduction subbands in the InAs well and light-hole subbands in the GaSb well is observed for larger InAs layer thickness. A "transition energy region'' resulting from the crossing of the respective subbands in the InAs and GaSb wells is also observed. The effect of the InAs layer induced subband properties related to the carrier transport in the peak current of the GaSb/InAs/GaSb/AlSb/InAs structure is also discussed.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6222-6226 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-band model that considers the coupling effects among the conduction band, light-hole band, and spin-orbit split-off–hole band is used to investigate carrier transport in InAs/AlSb/GaSb interband tunneling structures. The E-k relations and the boundary conditions suitable for the three-band model are derived from the Hamiltonian. Good agreement in the peak current density and peak voltage between experiments and model has been achieved. It is also found that the three-band model shows better agreement in the peak current densities than those of two-band model. It indicates the importance of the coupling effects of the spin-orbit split-off–hole band to the InAs/AlSb/GaSb interband tunneling structures. The valley current components, the key ingredient of the peak-to-valley current ratios, such as the thermionic currents and hole tunneling current, are studied to fit the experimental peak-to-valley current ratios. It is found that the thermionic currents can be neglected due to the large band offset (barrier height). The hole tunneling current, the major part of valley current, decreases with the AlSb barrier thickness. However, deviations from the experiments still exist. Furthermore, the effect of the band bending at the interfaces influences the I-V characteristics.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The voltage V versus current I of a high-quality YBa2Cu3O7−x thin film with zero-resistance temperature equal to 90.8 K was measured at temperatures near Tc (85, 87, and 90 K, respectively) under different magnetic fields (0–7 T). A significant result is that the critical-current density of the film reached 1.37×104 A/cm2 (zero field) even at 90 K, implying that strong pinning centers exist in our sample. However, a small applied magnetic field will diminish the critical-current densities remarkably. The pinning-force densities are found to follow Kramer's scaling law in both perpendicular and parallel directions of the magnetic fields to the c axis of the film. A possible influence of thermally activated flux creep on the pinning mechanism is confirmed.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 75-83 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Material line folding is studied in two-dimensional chaotic cavity flows. Line folding is measured by the local curvature k=l×l′/||l||3, where l(q) is an infinitesimal vector in the tangential direction of the line, q is a coordinate along the line, and l′ is the derivative of l with respect to q. It is shown both analytically and numerically that folding is always accompanied by compression. The vector l′ plays a crucial role as a driving force for the stretching and folding processes. A material line is stretched when l′ is tangential to the line and it is folded when l′ is normal to the line. The spatial structure of the curvature field is computed numerically. The short-time structure of the curvature field is similar to the structure of unstable manifolds of periodic hyperbolic points, and closely resembles patterns observed in tracer mixing experiments and in stretching field computations. The long time structure of the field asymptotically approaches an entirely different time-independent structure. Probability density functions of curvature are independent of both time and initial conditions. © 1996 American Institute of Physics.
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