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  • American Institute of Physics (AIP)  (19)
  • 2005-2009
  • 1990-1994  (19)
  • 1975-1979
  • 1935-1939
  • 1992  (19)
  • 1
    Electronic Resource
    Electronic Resource
    Enhanced carrier densities and device performance in piezoelectric pseudomorphic high-electron mobility transistor structures (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 1072-1074 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The addition of a piezoelectric field in AlGaAs/InGaAs/GaAs HEMT structures is shown to lead to enhanced electron densities and hence improved device performance. Growth of a strained InxGa1−xAs layer is in [111]A direction causes a piezoelectric field to be built into the quantum well of a pseudomorphic HEMT, which opposes the electric field due to charge transfer and hence lowers the confinement energy. This leads to carrier densities 50% larger than in equivalent [100] structures, with the wave function also spaced further away from the dopant impurities and the well interfaces. We expect these factors to give improved device performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107694
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  • 2
    Electronic Resource
    Electronic Resource
    Slit morphology of electromigration induced open circuit failures in fine line conductors (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 3201-3203 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed transmission and scanning electron microscopic images of electromigration-induced open circuit failures are presented for fine line aluminum alloy thin film interconnects. A characteristic slit open circuit, similar to stress migration open circuits in narrow interconnects, is shown for various film compositions, processing, and deposition conditions. It is suggested that slit failure morphology is more generally observed for low (≈1) ratios of conductor line width to film grain size. The slit failures observed often occur near copper rich precipitates. The morphology of several slit voids suggests that they are transgranular across the linewidth, consistent with other recent reports of electromigration induced damage in single crystal interconnects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351484
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of the transient spectral density of velocity fluctuations in GaAs and InP (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2322-2330 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a multiparticle Monte Carlo method, a theoretical analysis of the spectral density of velocity fluctuations in semiconductors has been performed, under both stationary and transient conditions (when the electric field applied to a semiconductor changes). In the case of the transient analysis a general method has been developed and applied to N-type GaAs and InP. The results obtained are interpreted in terms of the microscopic processes occurring during the transient. Significant differences between these materials have been observed. The following results were found: (i) The main source of noise is the presence of carriers in the Γ valley subject to the action of high fields, and the velocity-disorienting effect of the intervalley mechanisms; (ii) the maximum in the spectral density is essentially due to the presence of intervalley mechanisms; (iii) the dominant frequencies in the spectral density are strongly affected by the duration of the free flights; (iv) for long times, the transient spectral density converges on the steady-state one of the final field.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351574
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical study of the low-lying states of trans-1,3-butadiene (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7499-7506 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present extensive ab initio calculations on the low-lying electronic states of trans-1,3-butadiene within the multireference configuration interaction (MRCI) framework by selecting the configurations with a perturbative criterion. The X 1Ag ground state and 1 3Bu, 1 3Ag, 2 1Ag, and 1 1Bu valence excited states have been calculated at a fixed geometry. The results obtained are in good agreement with previous experimental and calculated values, and could help to understand polyene spectroscopy, photochemistry, and photophysics. The advantages of a MRCI method where the most important contributions to the total MRCI wave function, perturbatively selected, are treated variationally, and the remaining terms are evaluated by means of a perturbational approach, are also discussed. Furthermore, a criterion in order to build a correlation-consistent configuration interaction space is stated and, therefore, a reliable approximation to achieve accurate energy differences is obtained. Several monoelectronic molecular-orbital basis functions are tried in order to select the most adequate to describe each state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463521
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  • 5
    Electronic Resource
    Electronic Resource
    Vibrational–torsional coupling. High-resolution stimulated Raman spectrum of the ν3 band of ethane (12C2H6) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7055-7063 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a stimulated Raman spectrum of the Q branch of the ν3 band of ethane recorded with a resolution of about 0.0055 cm−1 and an absolute wave-number accuracy of the order of 0.001 cm−1. This spectrum is analyzed in terms of a vibrational–torsional coupling Hamiltonian that allows for the calculation of the observed wave numbers within the experimental uncertainty. The following spectroscopic parameters (in cm−1) have been obtained: ν30=994.1108(10), B3A1s−B0=−0.006 165(3), B3E3d−B0=−0.006 170(2), B3E3s−B0 =−0.006 184(2), B3A3d−B0=−0.006 257(2), A3A1s−A0=−0.003 037(15), A3E3d−A0 =−0.003 040(12), A3E3s−A0=−0.003 054(12), and A3A3d−A0=−0.003 065(12). A strong dependence of the threefold torsional potential barrier with respect to the q3 normal mode, ∂V3/∂q3=−275.9±1.4 cm−1, is deduced from the present analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463531
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  • 6
    Electronic Resource
    Electronic Resource
    Broadband heterodyne reflectometry on the W7-AS stellarator (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4653-4653 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A broadband heterodyne reflectometer, operating in the frequency range 75–110 GHz, has been installed and operated at the W7-AS Stellarator in Garching for the study of density fluctuations and fast density profile determination. Both local (LO) and signal (rf) oscillators can be swept over the whole frequency range. Due to the balanced detection scheme, all drifts, as well as the broadband noise of the BWO (rf and LO) oscillators, are canceled at the different downconversion stages. After installation on W7-AS, first results reproduced the original findings of the former homodyne system [J. Sanchez, H. J. Hartfuss, E. Anabitarte, A. P. Navarro, et al. Nucl. Fusion 30, 2383 (1990)] as well as new results on the radial distribution of density fluctuations have been obtained. A phase drift due to asymmetries in the spectrum around the last IF has been observed; this phenomenon is strongly dependent on the plasma conditions and could be caused by plasma rotation. It is presently under study. The system offers broadband operation together with the possibility to decouple phase and amplitude oscillations of the reflected beam. The high dynamic range (up to 80 dB) is able to overcome the large amplitude oscillations of the reflected beam. The reflectometer described offers a good basis for further developments on large devices, which will require a very high sensitivity due to the long waveguide runs, together with the advantage of the operation in a continuous frequency range and fast sweeping capability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143650
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  • 7
    Electronic Resource
    Electronic Resource
    Amplitude modulation reflectometry for large fusion devices : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4654-4656 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: One of the main problems which arises in density profile measurements by reflectometry is the need for continuous tracking of the phase delay; fast density fluctuations and strong modulation on the amplitude of the reflected signal can cause "fringe jumps'' in the phase signal. Amplitude modulation reflectometry performs a time delay measurement by the determination of the phase delay of the modulating envelope of a millimeter wave reflected by the plasma. The phase delays involved are small, the measurement is not affected by the fluctuations and can be directly performed without complicated fringe counters; the method provides a promising possibility for real time determination of the plasma position and density profile. In the present paper the principles of the method are presented as well as the analysis on the effects of phase and amplitude fluctuations, dispersive effects, and accuracy requirements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143651
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  • 8
    Electronic Resource
    Electronic Resource
    Two high brilliance beam lines at the ESRF dedicated to microdiffraction, biological crystallography, and small-angle scattering (invited) : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 974-981 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Two undulator beam lines will be available at the ESRF for microdiffraction/small-angle scattering (beam line 1) and time-resolved small-angle scattering/biological crystallography (beam line 4). In both cases a separate function optics with a double monochromator and a double focusing mirror have been selected. The general design principles of the two cameras, end station, and data acquisition systems foreseen are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143794
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  • 9
    Electronic Resource
    Electronic Resource
    Radial distribution of turbulence correlation lengths obtained by reflectometry in the TJ-I tokamak (abstract) : Proceedings of the 9th topical conference on high temperature plasma diagnostics (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 4657-4657 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A method for determination of radial correlation lengths of the electrostatic turbulence has been developed and applied to the TJ-I tokamak [T. Estrada, J. Sanchez, B. Brañas, and A. P. Navarro, Rev. Sci. Instrum. 61, 3034 (1990)]. The method uses homodyne detection and is based on the slow sweeping of one oscillator while the other remains at fixed frequency. The decay of the coherence can be observed as the distance between the two probing points increases. By the operation in the Q band (33–50 GHz) extraordinary mode, the system reaches most of the plasma radius. Correlation lengths obtained at the edge are compared with those measured at the plasma center. A critical issue for this comparison is the detailed knowledge of the local density gradient. The proposed method can provide the density profile information, avoiding the effect of lost fringes, even in the presence of turbulence. This fact can be used to determine the local density gradient which is needed to evaluate the separation between both reflecting points. Initial experimental results and a discussion on its degree of accuracy is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143652
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  • 10
    Electronic Resource
    Electronic Resource
    A conceptual model for ray tracing calculations with mosaic crystals : Proceedings of the 4th international conference on synchrotron radiation instrumentation (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 932-935 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Mosaic crystals provide an interesting choice for synchrotron radiation monochromators under certain conditions. They show a wider and lower reflectivity curve than perfect crystals, but a higher integrated reflectivity. Some mosaic crystals such as graphite or beryllium could be considered as monochromators or premonochromators for third generation synchrotron radiation machines (Sincrotrone Trieste, European Synchrotron Radiation facility, etc.). In order to assess these possibilities, we have implemented a new mosaic crystal part in the ray tracing code SHADOW. The effect of the random distribution of the crystallites in a mosaic crystal can be analyzed efficiently with a Monte Carlo method. Taking into account the random distribution of the crystal planes, modeled as a Gaussian of standard deviation κ, it is possible to reproduce the well known focusing and defocusing properties of these crystals. For reflectivity calculations we have implemented in the computer code the Mosaic Crystals Theory of Zachariasen. As secondary extinction is not negligible in mosaic crystals, we have also included the penetration effect of the x-ray beam inside the crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143784
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