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  • American Institute of Physics (AIP)  (15)
  • The American Association for Clinical Chemistry (AACC)  (1)
  • 1
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time resolved photoluminescence (PL) characteristics of a SiN cap disordered GaAs/AlGaAs multiple quantum well (MQW) structure exhibit a decrease in carrier lifetime in conjunction with an increase in quantum well disordering (QWD) as the SiN capping layer thickness is increased. The decrease in carrier lifetime is attributed to enhanced carrier trapping due to the defects introduced during dielectric cap quantum well disordering and the relaxation of the momentum conservation during radiative recombination by QWD. Potential applications of these effects on high speed optical devices such as laser diodes (LD's) and optical modulators are discussed. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence (PL) measurements at 10 K were performed in order to investigate the influence of electric fields on the exciton states in Al0.4Ga0.6As/GaAs asymmetric coupled multiple quantum wells (ACMQW) grown by molecular-beam epitaxy. The coupling of the electronic energy levels in the wells led to an enhancement of the quantum-confined Stark effect. The PL intensity decreased as the electric field increased. Calculated values of the intersubband transition energies were in good agreement with the experimental values for the ACMQW, and these values showed a similar behavior as those for the step quantum well. When the external applied field was very strong, Stark-ladder transitions were observed, and the measured dependence of the field-induced energy shifts of the Stark-ladder transitions for the ACMQW agreed with theory. These results indicate that the Stark effect and the Stark-ladder transitions in a unique ACMQW based on the AlxGa1−xAs/GaAs structure were observed simultaneously. © 1995 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3809-3811 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Probabilities are utilized to arrive at a relationship that defines the boundary for the monocrystalline region in terms of the partial pressure of the source gas and the deposition temperature. Also derived is a relationship for the average grain size of polycrystalline film. The results are restricted to the complete or near-complete condensation case of nucleation. © 1995 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Photoluminescence (PL) measurements were performed in order to investigate the carbon impurity effects on the intermixing behavior of GaAs/AlAs multiple quantum wells (MQWs) grown by molecular-beam epitaxy. The GaAs/AlAs MQWs were annealed with a carbon source in a furnace annealing system. The PL spectra show that the magnitude of the intermixing of Al and Ga induced by thermal annealing in GaAs/AlAs MQWs increases with depth. This behavior is not in agreement with the intermixing mechanism considering vacancy injection of the surface. The nonuniformity of the intermixing as a function of the depth originated from the carbon impurities which were injected during thermal treatment. © 1995 American Institute of Physics.
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  • 5
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A nine-channel interferometer/polarimeter system is designed for the RTP tokamak (Rijnhuizen Tokamak Project, a =0.16 m, R =0.72 m, BT =2.5 T, Ip ≤ 200 kA, and plasma pulse duration 200 ms). A CO2-pumped dual-cavity FIR laser system is used to obtain two FIR laser beams of λ =432 μm with a frequency difference of 1 MHz. The FIR beams are expanded by a set of parabolic mirrors. Corner-cube mixers with Schottky diodes are used as detectors. The mixers are mounted on a linear rail system, such that their positions can be easily changed. The interferometer can be operated with a maximum of 19 channels, and will be extended with a polarimeter to measure the poloidal magnetic field distribution. It will be tried to increase the accuracy of the polarimeter by modulating the polarization of the incoming beam. A scheme for polarization modulation which is based on the idea of Dodel and Kunz will be presented in this paper. This scheme has the advantage that only one set of detectors is needed to measure the electron density and current density. The complete system will be presented along with some pilot experiments concerning the polarization modulation.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Multichannel collective scattering of far-infrared (FIR) laser radiation is employed on the TEXT tokamak to investigate small-scale turbulent density fluctuations. A twin-frequency optically pumped FIR laser operating at 1222 μm ((approximately-equal-to)20 mW) and a difference frequency ΔωIF/2π(approximately-equal-to)1 MHz is used for the source and local oscillator beams. This permits heterodyne detection of the frequency-shifted scattered radiation which is necessary to determine wave propagation direction of plasma density fluctuations. The need for heterodyne versus homodyne detection is demonstrated. Such a diagnostic capability has allowed preliminary identification of the ion pressure-gradient-driven instability (whose most notable signature is that of turbulent fluctuations propagating in the ion diamagnetic drift direction) which is potentially responsible for saturation of the global energy confinement time with increasing density in tokamak plasmas.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6185-6187 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ferromagnetic Fe or Co was electrodeposited into the pores in aluminum anodic oxide film to produce a magnetic anodic film, and the effects of magnetic field during electrodeposition on the deposition characteristics of the metals and coercivity of the produced anodic film were investigated. Fe was electrodeposited into the pores in anodic film using a mixed solution (pH=3.8) of FeSO4(NH4)SO4.6H2O (0.20 mol/l) and H3BO4 (0.48 mol/l) at 20 °C with constant applied voltage of 10 V, and Co using a mixed solution (pH=4.5) of CoSO4,7H2O (0.10 mol/l) and H3BO4 (0.48 mol/l). It has been found that for the Fe-deposited anodic film the coercivity increased with increasing length of deposited Fe particles and decreased with increasing diameter (or porosity). The application of magnetic field during electrodeposition of Fe had little influence on the coercivity of the anodic film. For the Co-deposited anodic film the coercivity increased with increasing length of deposited Fe particles and increased unexpectedly with increasing diameter. The perpendicular coercivity of the Co-deposited anodic film was significantly increased by the application of magnetic field during the electrodeposition. The unexpected coercivity increase with diameter and the increase of the perpendicular coercivity of Co-deposited film by the application of magnetic field were closely related to the preferred orientation of Co crystals in the anodic film. © 2000 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 4120-4123 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We developed a simple current mode preamplifier for the microchannel plate (MCP) with the anode biased to high voltage. It uses a capacitor to block dc high voltage and measures the MCP current through the capacitor. Then it compensates exactly the distortion caused by the capacitor so the amplifier can measure any length of signals without distortion. It is much less expensive and simpler than using the phosphor screen system to isolate the dc high voltage. We derived a formula for that compensation and implemented it by using an op-amp's circuit. It gives an approximate time resolution of 10 μs which is restricted by the op-amp's characteristics. So, it may be improved by using fast op-amp's. This can also be used for channeltron and other electron multipliers. For the test of the preamplifier, we measured the photoelectron currents induced by the soft x rays radiated from the KT-1 tokamak of which the pulse length was 20 ms. The data revealed well, without distortion, the time evolution of the line radiation. © 1996 American Institute of Physics.
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  • 9
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Diffraction from plasma density irregularities can have significant consequences for the tomographic inversion of line-of-sight integrated measurements of the phase disturbance suffered by a probing beam. A new tomographic approach which takes account of diffraction from high-K refractive index structures is described. The relevance for multichannel interferometry measurements is demonstrated numerically and the technique is applied to the inversion of multichannel TEXT interferometer data.
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  • 10
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A multichannel, heterodyne, far-infrared laser interferometer with high spatial and phase resolution is employed on TEXT to characterize the equilibrium density profile for the full range of TEXT discharge parameters. Gaussian and parabolic functional fits with three free parameters are made to the measured profiles and compared. Scaling of the equilibrium density profile shape with plasma current, toroidal magnetic field, and density is clearly observed. By performing a regression analysis on each free parameter for the functional fit, one can construct a set of analytical relations describing the TEXT density profile for steady-state ohmic discharges. The database used to identify these relations contains 50 different discharge conditions.
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