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  • 1
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dynamics of photoexcited electrons in GaAs and InP were studied using the transmission of 200-fs pulses of far-infrared radiation in the spectral range 15–100 cm−1. Kinetic traces of the infrared transmission as a function of delay between optical excitation and infrared probe show a probe-limited decrease in transmission followed by a more gradual (0.7–2 ps) drop to a steady value, consistent with the slow return of electrons from high-mass satellite valleys. Infrared transmission spectra, analyzed in the context of a Drude model, reveal density-dependent electron mobilities 3–4 times below equilibrium n-doped values. Electron-hole collisions likely account for the lower mobility.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Interfacial reactions between (100) InP and thin films of the transition metals Cr, Ni, Pt, and Ti have been studied. A thin layer of metal was deposited onto the InP substrates using e-beam evaporation and parts of the samples were then subjected to heat treatment in vacuum for 30 min at several temperatures up to 500 °C. Separate characterizations of the metal, In, and P depth distributions were carried out using mass and energy dispersive recoil spectrometry. The different crystalline phases observed were determined using x-ray diffraction. The near-noble metals (Ni, Pt) formed ternary phases, while Ti and Cr formed phosphides. The phases formed were generally stable up to 500 °C with the major exception being Pt where the ternary phase decomposed to form PtIn2, PtP2, and Pt3In7. © 1996 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 2269-2271 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Guided acoustic-wave Brillouin scattering (GAWBS) measurements were performed on 20-cm lengths of optical fibers with particular attention focused on the lowest lying resonance. In 125-μm-diam silica fibers, this resonance was observed to occur at ∼22 MHz and have a line shape which varied erratically from sample to sample. Significant line shape fluctuations were evident even between sequential samples from the same fiber spool. We speculate that the observed effects are attributable to 0.01–0.1 μm distributed geometric deviations from a perfect cylinder. © 1994 American Institute of Physics.
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 3482-3484 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The crystallographic orientation dependence of the far-infrared (FIR) light generated at the (001) surface of a zincblende semiconductor is shown to derive principally from bulk difference-frequency mixing. A strong modulation is observed for 1-GW/cm2 pulses on InP, which demonstrates that the radiated FIR wave produced by bulk optical rectification is comparable to that generated by the transport of photoinjected carriers. Using the bulk rectification light as a clock, we show that more than 95% of the light produced from an InP (111) crystal by 100-fs, 100-μJ pulses is generated in a time shorter than the excitation pulse.
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 35 (1994), S. 1597-1621 
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The eigenvalue problem for the radial Schrödinger equation with an "almost'' Coulomb potential is considered. This problem provides the simplest example of a system whose classical trajectories have singularities. Thus the standard semiclassical quantization procedure (in the sense of Einstein–Brillouin–Keller–Maslov) cannot be applied straightforwardly to this situation. The equation under consideration has two transition points on the half axis 0〈x〈∞: a regular singular point at the origin and a turning point for some x0(approximately-greater-than)0; these points coalesce at low energy levels. The well-known comparison equation method provides uniform asymptotics for equations of this kind, but has the following shortcomings: it does not appeal to the corresponding classical mechanical problem and the formulas for the eigenvalues and eigenfunctions contain phase integrals which are not analytic with respect to the parameter characterizing the closeness of the transition points. In the present article we derive new formulas for the eigenfunctions in the form of inverse Fourier transforms of rapidly oscillating exponentials multiplied by some powers of x, together with simple formulas for the eigenvalues. These formulas are directly connected with the classical trajectories and do not have the shortcomings of the comparison equation method, i.e., all the functions entering the asymptotic expansions are analytic in x and energy. As a by-product, an asymptotic expansion of integrals having two stationary phase points which coalesce for some value of the parameter and tend to infinity when the parameter tends to zero is obtained.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 14 (2002), S. 938-945 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Temperature measurements have been made in a buoyancy driven mixing layer created by an unstable temperature gradient in water. Experiments were performed with a temperature difference of 5 °C, with a corresponding Atwood number of 7.5×10−4. Two types of analyses were used to determine density fluctuation correlations. The first analysis determined density fluctuation correlations from the mean density profiles, which is sufficient for a two-fluid distribution of the density where there was no molecular mixing. The second analysis used measurements taken from a continuous distribution of density, and thus included molecular mixing associated with heat diffusion. The thermocouples used for temperature measurements enabled the collection of large sample sizes and thus a detailed examination of molecular mix fractions, spectral properties of the density fluctuations, and probability distributions of the density through the mixing layer. © 2002 American Institute of Physics.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: CoSi2 exhibits the features of low resistivity and stability at elevated temperatures which make it interesting to employ for metallization on GaAs. The interfacial reactions in GaAs samples with thin film overlayers of Si and Co [Si(220 nm)/Co(50 nm)/(〈100〉-GaAs)] were studied using x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy, and mass and energy dispersive recoil spectrometry. Samples were vacuum furnace annealed for time periods between 1 and 8 h at temperatures ranging from 300 to 700 °C. It was found that a CoSi2 layer formed without observable reaction with the substrate at 500 °C and above. The excess Si (Si/Co atomic ratio of 2.41) remained near the surface as elemental Si and as SiO2 for the 500 and 600 °C annealings. For the 700 °C annealing the excess near-surface Si was not observed. © 1995 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 8 (1996), S. 3271-3287 
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed three-dimensional linear stability analysis, based on Floquet theory, to study the stability of finite amplitude internal gravity waves. This analysis has been used to compute instability growth rates over a range of wave amplitudes and propagation angles, especially waves above and below overturning amplitude, and identifies several new characteristics of wave instability. Computation of instability eigenfunctions has allowed us to analyze the energetics of the instability and to clarify the paths of energy transfer from the base wave to the instability. We find that the presence of wave overturning has no qualitative effect on the wave instability, except for the limiting case when the wavenumber vector is vertical. Instabilities which are nearly two-dimensional are closely related to second-order wave–wave interactions. But the three-dimensional instabilities, more prominent at higher wave amplitudes, may be caused by higher order resonance interactions. The energetics of the instabilities range from being shear driven to being driven by "density gradient'' production (the potential energy analog of "shear'' production); this characteristic is strongly dependent on wave propagation angle and the three-dimensionality of the instability. © 1996 American Institute of Physics.
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