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  • Artikel: DFG Deutsche Nationallizenzen  (10)
  • 1990-1994  (10)
  • 1
    Digitale Medien
    Digitale Medien
    Growth of zinc blende-GaN on β-SiC coated (001) Si by molecular beam epitaxy using a radio frequency plasma discharge, nitrogen free-radical source (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6124-6127 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the growth of zinc blende-GaN epitaxial films on β-SiC coated (001) Si substrates using a molecular beam epitaxy approach in which the reactive nitrogen species are generated in a remote 13.56 MHz rf plasma discharge, nitrogen free-radical source. We postulate, based on optical emission spectroscopy studies of the remote plasma, that, in our study, nitrogen atoms are the species primarily responsible for efficient nitridation. The zinc blende nature of the GaN films was confirmed by in situ reflection high-energy electron diffraction, ex situ x-ray diffraction, and ex situ low-temperature photoluminescence analyses. Our zinc blende-GaN film growth rates (∼0.3 μm/h) are higher than those reported to date that involve the use of electron cyclotron resonance type reactive nitrogen sources.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.355176
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  • 2
    Digitale Medien
    Digitale Medien
    Growth by molecular beam epitaxy and electrical characterization of Si-doped zinc blende GaN films deposited on β-SiC coated (001) Si substrates (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 91-93 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report the electrical characteristics of heavily Si-doped zinc blende GaN epilayers deposited on β-SiC coated (001) Si substrates. The β-GaN films were grown by molecular beam epitaxy using a rf plasma discharge, nitrogen free-radical source, and the doping concentration in the films was controlled over the range 1.5×1018–3.0×1020 cm−3 by suitably adjusting the temperature of a Si effusion cell. We have found that Si incorporation in β-GaN results in a relatively deep donor level (∼62 meV below the conduction band edge at a carrier concentration at room temperature of 1018 cm−3). Also, we present evidence of simultaneous high mobility conduction band conduction (dominant at high temperatures) and low mobility impurity band conduction (dominant at temperatures 〈70 K) in heavily doped (nRT(approximately-greater-than)1019 cm−3) material.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.113085
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  • 3
    Digitale Medien
    Digitale Medien
    Optical response of nongranular high-Tc Y1Ba2Cu3O7−x superconducting thin films (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3054-3068 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have investigated the optical response of c-axis oriented crystalline Y1Ba2Cu3O7−x thin films (bridge and meander devices) on strontium titanate and MgO substrates. cw optical response to a He-Ne laser radiation (wavelength of 0.63 μm) was primarily bolometric. The pulsed optical response was studied with Q-switched and mode-locked Q-switched short pulses from a Nd:YAG laser at the wavelength of 1.06 μm. We identify two distinct components contributing to the pulsed optical response: a nonbolometric (as fast as 1 ns) and a bolometric component (several ns). The bolometric component is strong at temperatures in the vicinity of the transition region to the normal state. The nonbolometric component is dominant at temperatures below the transition region showing weak temperature dependence and a linear dependence on the bias current. These results are discussed using the flux motion model and also electron-phonon scattering relaxation dynamics of nonequilibrium superconductors based on the theory of Bardeen-Cooper-Schrieffer. The results suggest that with proper optimization of device parameters (geometry, critical current density, etc.) sensitive bolometers and high-speed detectors covering a broad electromagnetic spectrum (visible and infrared) may be developed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.345435
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  • 4
    Digitale Medien
    Digitale Medien
    Dynamic electrical response of Y1Ba2Cu3O7−x (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 3767-3775 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We studied the dynamic electrical properties of epitaxial Y1Ba2Cu3O7−x superconducting thin films on strontium titanate and MgO substrates. A fast nonlinear switching of a high-Tc film between the dissipative and superconducting states has been demonstrated. These measurements show that the rise and the fall times of these transitions are faster than 250 ps (which are presumably limited by the speed of the measurement electronics). This fast nonlinear switching may lead to opportunities for new high-frequency electronic devices including, for example, fast logic gates or threshold devices. We have proposed and demonstrated the application of such a nonlinear switching in a novel noise discrimination scheme for speeds of several hundred MHz. The proposed method is simple and effective in the enhancement of signal-to-noise ratio in digital electronic circuits.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.345021
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  • 5
    Digitale Medien
    Digitale Medien
    Photoresponse and Optical Detection with High Temperature Superconducting Thin Films (1993)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 130-132 (Jan. 1993), p. 303-314 
    Details
    ISSN: 1662-9752
    Quelle: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Thema: Maschinenbau
    Materialart: Digitale Medien
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/00/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.130-132.303.pdf
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  • 6
    Digitale Medien
    Digitale Medien
    On the convection of a passive scalar by a turbulent Gaussian velocity field (1991)
    Springer
    Journal of statistical physics 63 (1991), S. 305-313 
    Details
    ISSN: 1572-9613
    Schlagwort(e): Turbulence ; diffusion ; helicity ; convection ; incompressible fluids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Through the use of the Novikov-Furutsu formula for Gaussian processes an equation is obtained for the diffusion of the ensemble average of a passive scalar in an incompressible turbulent velocity field in terms of the two-point, two-time correlator of this field. The equation is valid for turbulence which is not necessarily homogeneous or stationary and thus generalizes previous work.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01026606
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  • 7
    Digitale Medien
    Digitale Medien
    The relation between the average complexity of high-tech products and their diversity: An empirical test of evolutionary models (1994)
    Springer
    Journal of evolutionary economics 4 (1994), S. 273-288 
    Details
    ISSN: 1432-1386
    Schlagwort(e): Technometrics ; Technological excellence ; Innovation ; Schumpeter ; Evolutionary models ; O30 ; O33
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Wirtschaftswissenschaften
    Notizen: Abstract What is the relation between the average level of complexity that characterizes a product's technology, and the degree of diversity of that technology across rival firms? Evolutionary theories of innovation and technical advance are consistent with either a direct or an inverse relation. The issue thus becomes an empirical one. This paper uses a unique database containing detailed quantitative data on the specifications of 12 high-tech product groups for the U.S., Japan and selected European countries, for 1982, for both products and processes. It is found that the more complex the technology, the less diverse is the technology of rival firms that produce the product. This is consistent with the following evolutionary process: Economies of scale and scope inherent in high-level technologies require firms who adopt them to dispose entirely of older technologies, in order to remain competitive; at the same time, older, simpler technologies continue to exist and permit wide diversities among firms who pursue “niche” market strategies.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01236407
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  • 8
    Digitale Medien
    Digitale Medien
    Interactions of coherent structures in a film flow: Simulations of a highly nonlinear evolution equation (1994)
    Springer
    Theoretical and computational fluid dynamics 6 (1994), S. 235-254 
    Details
    ISSN: 1432-2250
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Numerical simulations of the evolution equation [14] for thickness of a film flowing down a vertical fiber are presented. Solutions with periodic boundary conditions on extended axial intervals develop trains of pulse-like structures. Typically, a group of several interacting pulses (or a solitary pulse) is bracketed by spans of nearly uniform thinned film and is virtually isolated: The evolution of such a “section” is modeled as a solution with periodic boundary conditions on the corresponding, comparatively short, interval. Single-pulse sections are steady-shape traveling waveforms (“cells” of shorter-period solutions). The collision of two pulses can be either a particle-like “elastic” rebound, or—and only if a control parameter S (proportional to the average thickness) exceeds a certain critical value, S c ≈ 1—a “deeply inelastic” coalescence. A pulse which grows by a cascade of coalescences is associated with large drops observed in experiments by Quéré [39] and our S c is in excellent agreement with its laboratory value.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00417922
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  • 9
    Digitale Medien
    Digitale Medien
    Thermal and nonequilibrium responses of superconductors for radiation detectors (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 871-884 
    Details
    ISSN: 1572-9605
    Schlagwort(e): Superconducting radiation detectors ; photoresponse ; nonequilibrium optical response ; optical properties ; thermal design
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract This work summarizes the progress in the study of the superconductor response to optical radiation and in the development of infrared detectors. The recent advances in the design of high-T c superconducting radiation detectors using silicon microfabrication technology are emphasized. Thermal and optical properties important for the detector performance are discussed. The mechanism of the nonequilibrium optical response and its potential use to build fast and sensitive radiation detectors are described. Future challenges and opportunities in the development of high-T c superconducting radiation detectors are highlighted.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00732263
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  • 10
    Digitale Medien
    Digitale Medien
    Cooperation between Israeli and foreign researchers (1992)
    Springer
    Scientometrics 25 (1992), S. 381-400 
    Details
    ISSN: 1588-2861
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Buch- und Bibliothekswesen, Informationswissenschaft , Wissenschaftskunde und Wissenschaftsorganisation, Hochschul- und Universitätswesen, Museumswissenschaft
    Notizen: Abstract This paper analyses the reasons, framework and trends of scientific cooperation between Israeli and foreign researchers for the period 1974–1983. The study used the ISI database purchased by the S. Neaman Institute, containing all Israeli publications for the above mentioned years. A complementary survey was carried out including a sample of two academic institutions. The survey database established on the basis of replies of 249 researchers who replied to the survey questionnaires includes data regarding 5,893 papers, 1550 of which had not been included in the ISI database. The findings show that about one third of the papers missing from the ISI database is due to the fact that authors did not note their permanent Israeli address under the paper's title. Other reasons for the partial coverage of the ISI database is that the ISI database does not cover all the professional journals and all types of scientific publications. The, survey points to an absolute increase of the actual bulk of the research performed by Israeli scientists abroad. Major differences were found between researchers among different departments as regards framework for research performed abroad, reasons and sources of funding. The main reason listed for foreign cooperation was that of true cooperation (50%) and this is a very positive phenomenon.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02016927
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