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  • 1
    Digitale Medien
    Digitale Medien
    Tetrakis(1-methylimidazole-N3)zinc(II) Diperchlorate (1996)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 52 (1996), S. 2482-2484 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270196007706
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  • 2
    Digitale Medien
    Digitale Medien
    Theoretical studies of radical recombination reactions. 4. An AM1/CI study of reactions of benzylic and allylic radicals. An intrinsic barrier to bond formation (1991)
    s.l. : American Chemical Society
    The @journal of organic chemistry 56 (1991), S. 6367-6371 
    Details
    ISSN: 1520-6904
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1021/jo00022a028
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  • 3
    Digitale Medien
    Digitale Medien
    Ambipolar diffusion and carrier lifetime measurements in all-binary (InAs)2(GaAs)5 strained quantum wells grown on GaAs (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 1868-1873 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The in-well ambipolar diffusion coefficients and carrier lifetimes in ordered all-binary quantum wells, composed of (InAs)2(GaAs)5 short-period strained-layer superlattices (SPSLSs) grown on [001]-oriented GaAs substrates, are measured using picosecond optically induced transient grating and pump-probe techniques. Quantum wells containing SPSLSs may be expected to exhibit higher in-plane hole mobilities compared to InGaAs ternary alloy quantum wells because of a larger average indium content and reduced disorder scattering in the SPSLS structures. The results obtained in the SPSLSs are compared to those obtained in InGaAs alloy quantum wells of comparable well width and confinement energies. This indicates that, for a given SPSLS and its equivalent alloy, the ambipolar diffusion coefficients are comparable while the carrier lifetimes in the SPSLSs are longer. The longer carrier lifetimes in the SPSLSs suggest that these binary structures possess fewer nonradiative recombination centers than the alloys. The absence of a dramatic improvement in the transport properties, however, may indicate that imperfect interfaces in the SPSLSs may be offsetting their possible advantages, in spite of the fact that optical measurements in the SPSLSs indicate high quality and x-ray and transmission electron microscopic measurements demonstrate the binary nature of these structures.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.355301
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  • 4
    Digitale Medien
    Digitale Medien
    Thin-film BiPbSrCaCuO direct current superconducting quantum interfering devices operating at 78 K (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7629-7631 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Direct current SQUIDs (superconducting quantum interference devices) have been successfully fabricated by using a Pb-doped BiSrCaCuO superconducting thin film made by mixed evaporation of a single source composed of related components with a resistance heater. The dc SQUID comprises a square washer with a small hole. These SQUIDs show perfectly periodic voltage-flux characteristics without magnetic shield, that is, typically, the flux noise and energy resolution at a frequency range from dc to 1 Hz and at 78 K being 1.7×10−3 Φ0/(square root of)Hz and 3.6×10−26 J/Hz, respectively. Meanwhile, we have found out that one of the SQUIDs still was able to operate on flux-locked mode without bias currents and showed voltage-flux second harmonic characteristics. This phenomenon is not well understood, but it may be related to I-V (current-voltage) characteristics of the dc SQUID.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.349722
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  • 5
    Digitale Medien
    Digitale Medien
    Room-temperature optical nonlinearities in strained (InAs)2(GaAs)5 superlattice quantum wells (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 3243-3248 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report room-temperature measurements of the nonlinear absorption cross section, σeh, and the nonlinear refraction coefficient, neh, associated with saturation of excitonic absorption and bandfilling, for high-quality multiple quantum well (MQW) structures in which each well consists of a highly strained, all binary (InAs)2(GaAs)5 short-period superlattice. The three samples studied, which have effective well thicknesses of 10.7, 14.8, and 18.8 nm, respectively, each display clearly resolved excitonic resonances at room temperature. Picosecond nonlinear transmission and transient grating measurements were performed on each sample in the spectral vicinity of the n = 1 heavy-hole excitonic resonance. The peak values of neh and σeh extracted from these measurements are comparable to those measured in high-quality GaAs/AlGaAs and unstrained InGaAs/InP MQWs. We determine the dependence of σeh and neh on the width of the quantum wells, and we discuss the fluence dependence of the nonlinearities. Consistency between the differential transmission and transient grating diffraction efficiency is demonstrated via a Kramers–Kronig analysis of the differential transmission spectra.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.348544
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  • 6
    Digitale Medien
    Digitale Medien
    Enhanced ambipolar in-plane transport in an InAs/GaAs hetero-n-i-p-i (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3860-3866 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In-plane transport in an InAs/GaAs semiconductor hetero-n-i-p-i has been investigated using picosecond transient grating techniques and an order-of-magnitude enhancement of the ambipolar transport relative to that measured in a similar undoped sample has been demonstrated. Both the magnitude and the density dependence of this enhanced transport are consistent with an additional driving force that is associated with an in-plane modulation of the screened n-i-p-i field. This modulation is the result of the spatial separation by perpendicular transport of electrons and holes that also have an in-plane density modulation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.352897
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  • 7
    Digitale Medien
    Digitale Medien
    Picosecond optical nonlinearities in a strained InAs/GaAs hetero n-i-p-i structure (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 929-932 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The nonlinear optical properties of a n-i-p-i structure containing strained superlattice quantum wells in the intrinsic regions are studied using picosecond pump and probe pulses of the same photon energy. For pump fluences as low as 1.1 μJ/cm2, a blue shift of the excitonic resonance, caused by the screening of the built-in space-charge field and the accompanying reduction in the quantum-confined Stark effect, is clearly observed. At higher fluences, the onset of bleaching of the excitonic absorption is observed. The nonlinearities associated with the quantum confined Stark effect in the hetero n-i-p-i are directly compared to those arising from excitonic bleaching in identical strained superlattice quantum wells under flatband conditions. The picosecond time resolution allows a more accurate estimation of the carrier density in the hetero n-i-p-i by ignoring the density-dependent recombination and a quantitative comparison between the strength of the nonlinearities in the two structures. Although such comparisons depend on the optical fluence and structure of the hetero n-i-p-i, we find that the magnitudes of the nonlinearities in these two specific structures are comparable on a per carrier basis, although their spectral signatures are quite distinct.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351315
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  • 8
    Digitale Medien
    Digitale Medien
    Optical nonlinearities and ultrafast charge transport in all-binary InAs/GaAs strained hetero n-i-p-i's (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6891-6897 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We use picosecond differential spectroscopy to temporally and spectrally resolve the formation and decay of nonlinearities and space-charge fields in a hetero n-i-p-i that contains quantum wells in the intrinsic regions that are composed of all-binary InAs/GaAs short-period strained-layer superlattices. The evolution of the optical response is determined by competition between excitonic bleaching and the excitonic shift caused by screening of the built-in electric field of the n-i-p-i. The relative contributions of the two resulting optical nonlinearities are complicated functions of fluence, time, and wavelength, with the detailed dynamics determined by thermionic emission from the wells, picosecond charge transport over nanometer dimensions, screening, and recombination. At low fluences, excitonic bleaching is the source of an ultrafast nonlinear response that can be turned on and off in 〈10 ps. This initial excitonic bleaching gives way to a blue shift of the exciton as the carriers escape the wells in ∼3 ps and drift to screen the built-in field in 〈10 ps. The blue shift persists until the carriers recombine nonexponentially on microsecond time scales. At higher fluences, excitonic bleaching and the blue shift are observed simultaneously, since only a fraction of the carriers are required to screen the field and the wells remain partially occupied. On the time scale of ∼10 ns, the bleaching contribution disappears as the carriers within the wells recombine, leaving only the persistent blue shift.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.349813
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  • 9
    Digitale Medien
    Digitale Medien
    Test particle transport from long-range collisions : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1552-1558 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Enhanced cross-magnetic-field diffusion of test particles in pure ion plasmas has been measured. The ion plasma is contained in a Penning-Malmberg trap for weeks near thermodynamic equilibrium, characterized by rigid rotation and uniform density and temperature. Plasma expansion and loss is suppressed by a "rotating wall" technique, i.e., a weak electrostatic potential rotating faster than the plasma. Test particle transport is then measured even though there is zero net transport, in a regime where neutral collisions are negligible. The observed test particle transport is diffusive, i.e., proportional to the gradient of the test particle concentration. The measured diffusion coefficients scale as nT−1/2B−2 over a range of 40 in density, 50 in temperature, and 5 in magnetic field. This diffusion is about ten times greater than predicted by classical collisional theory, which describes velocity-scattering collisions with impact parameters ρ(approximately-less-than)rc. The enhanced transport is thought to be due to non-velocity-scattering "E×B drift" collisions with rc〈ρ(approximately-less-than)λD. Initial estimates of diffusion due to these long-range collisions are three times less than the measurements, and substantial theory questions remain. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.872359
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  • 10
    Digitale Medien
    Digitale Medien
    Crystalline order in laser-cooled, non-neutral ion plasmas (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 7 (2000), S. 7-13 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Laser-cooled trapped ions can be strongly coupled and form crystalline states. In this paper we review experimental studies that measure the spatial correlations of Be+ ion crystals formed in Penning traps. Both Bragg scattering of the cooling-laser light and spatial imaging of the laser-induced ion fluorescence are used to measure these correlations. In spherical plasmas with more than 2×105 ions, body-centered-cubic (bcc) crystals, the predicted bulk structure, are the only type of crystals observed. The orientation of the ion crystals can be phase locked to a rotating electric-field perturbation. With this "rotating wall" technique and stroboscopic detection, images of individual ions in a Penning trap are obtained. The rotating wall technique also provides a precise control of the time-dilation shift due to the plasma rotation, which is important for Penning trap frequency standards.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873818
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