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  • 1980-1984  (4)
Materialart
Erscheinungszeitraum
Jahr
  • 1
    Digitale Medien
    Digitale Medien
    s.l. : American Chemical Society
    Journal of medicinal chemistry 23 (1980), S. 1222-1226 
    ISSN: 1520-4804
    Quelle: ACS Legacy Archives
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    ISSN: 1432-0630
    Schlagwort(e): 68.55.+b ; 72.00.Fr ; 73.40.Lq ; 85.30.De
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract In selectively dopedn-AlxGa1−xAs/GaAs heterostructures with high-mobility two-dimensional electron gas (2 DEG) at the heterointerface a second conductive channel exists, if the AlxGa1−xAs layer is not totally depleted from free carries. The occurrence of parallel conductance has a deleterious effect on the performance of high-electron mobility transistors (HEMTs) fabricated from this material. Although in principle computable, parallel conductance depends on a large number of design parameters to be chosen for the heterostructure, which are additionally affected by the presence of deep electron traps inn-AlxGa1−xAs of composition 0.25〈x〈0.35. Capacitance-voltage, Hall effect, and transverse magnetoresistance measurements in the temperature range 4–300 K were used to detect the undesired parallel conductance and to demonstrate its effect on the result of these evaluation techniques. In addition, the significant influence of parallel conductance on the dc properties of HEMTs fabricated from selectively dopedn-AlxGa1−xAs/GaAs heterostructures is shown.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    ISSN: 1432-0630
    Schlagwort(e): 72.20.Fr ; 72.20.Ht ; 72.20.My ; 73.40.Lq
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract The transport properties of warm and hot electrons in selectively dopedn-Al x Ga1−x As/GaAs heterostructures created by electric fields up to 500 V/cm were studied by Hall effect, conductivity, and Shubnikov-de Haas measurements at lattice temperatures from 4.2 to 300 K. Hall measurements revealed a substantial decrease of electron mobility and also of sheet electron concentration at 77 K with enhanced electric field. The accelerated 2D electrons are partly scattered into the low-mobility first excited (E 1) subband, and they are partly trapped in immobile states located in the AlxGa1−xAs near the interface. Consequently, two differentv(E) characteristics were obtained at 77 K. The 2D electrons populating only the lowest (E 0) subband exhibit a velocity of v∼-2×107 cm/s at 500 V/cm, while the averaged velocity due to all electrons reaches a value of v∼-1.5×107cm/s at 500 V/cm. The analysis of the Shubnikov-de Haas oscillations and Fast Fourier transformation of the data manifested that the 2D electrons are very rapidly accelerated at 4.2 K and achieve electron temperatures much higher than the lattice temperature at electric fields as low as 1 V/cm. The major cooling process for these electrons is scattering into the low-mobilityE 1 subband.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    ISSN: 0021-8383
    Schlagwort(e): Chemistry ; Organic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Photoinduced Decomposition of Arene Diazonium Salts by Pyrazolone and Naphthole DyesThe pyrazolone dyes 1-4 in their photoexcited singlet states bleached out by arene diazonium salts which dediazoniate during the reaction. Both compounds react in equal proportion. The quantum yields increase with the increasing of the concentration and electron acceptor properties of the diazonium salts and increasing of the electron donor properties of the dyes.The quantum yields of dye bleaching decrease on addition of DABCO or allylic thiourea, whereas the dediazoniation is not influenced. A kinetic model based on a primary electron transfer from the excited dye to arene diazonium salt is presented and used to determine rate constants for individual partial reactions.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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