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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transient electroluminescence (EL) from single- and multilayer organic light-emitting diodes (OLEDs) was investigated by driving the devices with short, rectangular voltage pulses. The single-layer devices consist of indium-tin oxide (ITO)/tris(8-hydroxy-quinoline)aluminum (Alq3)/magnesium (Mg):silver (Ag), whereas the structure of the multilayer OLEDs are ITO/copper phthalocyanine (CuPc)/N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB)/Alq3/Mg:Ag. Apparent model-dependent values of the electron mobility (μe) in Alq3 have been calculated from the onset of EL for both device structures upon invoking different internal electric field distributions. For the single-layer OLEDs, transient experiments with different dc bias voltages indicated that the EL delay time is determined by the accumulation of charge carriers inside the device rather than by transport of the latter. This interpretation is supported by the observation of delayed EL after the voltage pulse is turned off. In the multilayer OLED the EL onset—dependent on the electric field—is governed by accumulated charges (holes) at the internal organic-organic interface (NPB/Alq3) or is transport limited. Time-of-flight measurements on 150-nm-thin Alq3 layers yield weak field-dependent μe values of the order of 1×10−5 cm2/Vs at electrical fields between 3.9×105 and 1.3×106 V/cm. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3229-3232 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new beamline for radiometric applications (e.g., detector calibration and reflectometry) has been installed and characterized at the laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY. The beamline is equipped with a SX700 type plane grating monochromator and a toroidal mirror behind the exit slit of the monochromator for collimating the radiation to allow angle resolved reflectometry. A divergence of 0.1 mrad has been achieved. The beamline has been optimized for high spectral purity of the radiation. Within the photon energy range from 40 to about 1500 eV the total amount of stray light and higher order radiation stays below 1%. A photon flux of up to 1011 s−1 has been measured in the focal point of the toroidal mirror. It corresponds to a radiant power of a few μW and thus allows use of a cryogenic radiometer for detector calibration. The details of the beamline layout and the results of the performance characterization are presented.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2248-2250 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: At the radiometry laboratory of the Physikalisch-Technische Bundesanstalt (PTB) a reflectometer for the soft x-ray spectral region has been operated for several years utilizing monochromatic radiation of a toroidal grating monochromator or a high-resolution plane grating monochromator. The monochromators cover the photon energy region from 35 to 1500 eV. New challenges due to the development of soft x-ray optical components led to the design of a second reflectometer with advanced capabilities. Samples with a diameter of up to 250 mm can be accommodated. The time required for sample exchange is reduced by using a lock chamber. The feasibility of sample positioning with high precision has been improved. Typical uncertainties of about 1%–2%, e.g., for the reflectance of multilayer mirrors, can be achieved. A detailed description of the reflectometer as well as some typical results showing the performance are presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 2570-2573 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The x-ray transmission properties of a very thin polyimide window in the range 7–310 A(ring) have been investigated. The window is nominally 0.24 μm thick and is supported by a hexagonal polyimide grid. Transmission of over 60% and 80% at the oxygen Kα and carbon Kα lines, respectively, have been achieved. The use of such windows as the entrance window of a gas scintillation counter (GSPC) operating as a broadband spectrometer at XUV wavelengths is discussed. Overall detector efficiencies of greater than 10% for wavelengths less than 150 A(ring) are possible to achieve. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 9 (1962), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have observed intrinsic Josephson effects for current flow perpendicular to the CuO2 planes in HTSC thin films. Tl-Ba-Ca-Cu-O thin films were deposited on step edges in LaAlO3 substrates. Due to the special preparation process, microbridges across such steps act as stacks of intrinsic Josephson junctions with current flow perpendicular to the CuO2 planes (STEP STACK junctions). Up to 130 individual junctions could be observed exhibiting high IcRN products up to 26 mV per junction. We observed ac-Josephson effects as Shapiro steps and in microwave emission experiments. At low temperatures sharp emission peaks were detected at frequencies of 11.3 and 24.2 GHz. Broad emission peaks from the whole stack were observed at temperatures close to Tc. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the results of structural, chemical, and extreme ultraviolet (EUV) characterization of Si/Mo multilayers grown by sputtering and by UHV evaporation. This study includes mirrors designed for normal incidence with peak reflectivities Rpeak between 22 and 24 nm, and 45° mirrors having Rpeak between 16 and 19 nm. The deposition conditions were varied to produce multilayers with a wide range of interface morphologies. A variety of techniques were used to determine the structure and composition of the multilayers, including x-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy, and Auger depth profiling. All of the mirrors have amorphous Si layers and polycrystalline Mo layers with thin amorphous alloy interlayers. We obtain good fits to the low-angle x-ray diffraction data only when these interlayers are taken into account. The best sputter-deposited mirrors were made at the lowest Ar pressure studied, 3 mTorr. The best evaporated mirrors were produced at a substrate temperature of 200 °C. The EUV reflectivity as a function of wavelength was measured using synchrotron radiation. Both the multilayer structure and surface contamination significantly affect the EUV reflectivity, and must be considered to obtain good fits to the reflectivity curves. The best 45° mirror had a peak reflectivity of 53% at 18.6 nm for 100% S-polarized light, and the best normal-incidence mirror had a peak reflectivity of 33% at 23.6 nm.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 3814-3821 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Semi-insulating Fe-doped 〈100〉-InP wafers were implanted in a nonchanneling direction with 300 keV Si+ and 600 keV Se++ ions in the dose range of 1×1012–1×1016 cm−2. The implantation temperature was varied between room temperature and 425 K. The samples were capped and short time annealed by means of a graphite strip heater at 700–975 °C. The defect investigation of the as-implanted as well as of the annealed samples was performed with Rutherford backscattering spectrometry. A simple vacancy diffusion model is applied to describe the damage production, which yields critical implantation temperatures for amorphization. These temperatures are approximately 390 K for Si and 420 K for Se, for higher temperatures amorphization is not possible in InP. The electrical properties of the annealed layers are measured by the van der Pauw–Hall technique. The results are discussed with respect to the residual damage after annealing. Saturation values of the electrical activation were achieved at 3×1014 cm−2 for Si and 4×1014 cm−2 for Se, respectively.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 7138-7143 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial Pb1−xSnxSe layers have been grown on Si substrates, and Schottky-barrier infrared sensors were fabricated in the layers using Pb blocking contacts. The observed current–voltage characteristics (saturation currents j0 and ideality factors n) as a function of temperature are quantitatively explained with a fluctuation model of the barrier heights [J. H. Werner, W. Güttler, J. Appl. Phys. 69, 1991 (1522)]. The amount of the mean barrier fluctuation σ, which is typically 10–30 meV, depends on the layer quality and fabrication procedure. Higher σ causes higher j0 with increasing saturation values at low temperatures. In addition, the fluctuations cause high n(〉2) values at low temperatures. Layers with improved structural quality (higher mobilities and lower threading dislocation densities) lead to lower barrier fluctuations and, therefore, to increased sensitivities. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1911-1916 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Epitaxial growth of PbSe on (111)- and (100)-oriented Si substrates without an intermediate buffer layer is studied. It is found that on Si(111) the orientation of the IV-VI layer can by varied from (100) at 200 °C to (111) at 400 °C substrate temperature. On Si(100), only (100)-oriented layers were obtained for the whole temperature range. (100)-oriented layers with thicknesses above 0.5 μm were cracked due to thermally induced mechanical strain on cooldown to room temperature. This strain cannot be relaxed by dislocation glide in the first glide systems as it is the case for (111)-oriented layers. The structural quality of (100)-oriented PbSe layers on Si(100) and Si(111) is inferior compared to layers grown with an intermediate BaF2/CaF2 or CaF2 buffer layer. This implies that the covalent/ionic PbSe/Si interface seems to impede high-quality epitaxy, contrary to the well known ionic/ionic IV-VI/IIa-fluoride interface. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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