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  • 1
    ISSN: 0275-1062
    Keywords: RS CVn binaries ; white light flares
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0630
    Keywords: 61.10 ; 68.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Single crystals of iodine-intercalated C60 have been examined by transmission electron microscopy. Tilting series of Electron Diffraction Patterns (EDP) confirm that it has a simple hexagonal structure with c/a≈1 in accordance with the results of X-ray diffraction, which allows higher precision c/a=1.0024. Cooling and heating experiments were performed in the vacuum of the microscope to investigate the order — disorder phenomena. High-Resolution Electron Microscopy (HREM) images and electron diffraction patterns reveal that the c/2-displacement along the c-direction plays an important role in the transition from the simple hexagonal structure into the fcc structure when iodine is lost from the specimen or “vice versa”. The orientation relationship between the intercalate and the C60 structure is [01 $$\overline {\text{1}}$$ 10]h∥[1 $$\overline {\text{1}}$$ 10]fcc and (001)h∥(110)fcc. A model is proposed to interpret the features observed in EDP and HREM consistently.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present an experimental and theoretical study of the size dependence of the coupling between electron–hole pairs and longitudinal-optical phonons in Ga1−xInxN/GaN-based quantum wells and quantum boxes. We found that the Huang–Rhys factor S, which determines the distribution of luminescence intensities between the phonon replicas and the zero-phonon peak, increases significantly when the vertical size of the boxes or the thickness of quantum well increases. We assign this variation to (1) the strong electric field present along the growth axis of the system, due to spontaneous and piezoelectric polarizations in these wurtzite materials, and (2) the localization on separate sites of electrons and holes in the plane of the wells or boxes, due to potential fluctuations in the ternary alloy. Indeed, envelope-function calculations for free or localized excitons, with electron–hole distance only controlled by Coulomb interaction, do not account quantitatively for the measured behavior of the S factor. In fact, the latter is rather similar to what is obtained for donor–acceptor pairs, with a statistical distribution of distances between localization centers for electrons and holes. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 1674-1676 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: ZnxCd1−xSe epilayers were grown by organometallic vapor phase epitaxy using various VI/II flow ratios at a temperature of 420 °C. Cathodoluminescence (CL) spectroscopy and imaging were used to study their luminescent properties. Both near-band gap emissions (NBE) and deep-level emissions (DLE) were found in the CL spectra. We found that the width of the NBE peak and the intensity of the DLE relative peak to that of NBE increase with an increase in the VI/II flow ratio. Both effects are traced to the presence of pyramidal growth hillocks on the surface of the epilayer and to their increased density at high VI/II ratios. Monochromatic CL images show that there are two kinds of luminescent centers contributing to the NBE. The one that emits at slightly lower energies is only found, together with the DLE centers, within the growth hillocks. The one that emits at a slightly higher energy is found from surrounding areas. The concomitant appearance of DLE centers and low energy NBE centers shows that they share a common origin. Excitation intensity dependence of the photoluminescence of the NBE centers identifies as donor–acceptor-pair recombinations. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 79 (2001), S. 1127-1129 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: ZnSe epilayers were grown on a (001) GaAs substrate by metalorganic chemical-vapor-phase deposition. An interruption of the Zn source (i.e., Se passivation) was purposely introduced during the growth. The optical properties of the epilayers grown were studied by photoluminescence (PL) spectroscopy. We show that Se passivation during the growth interruption introduces luminescent centers in the epilayers. Evidence of this assignment comes from the characteristic temperature and excitation wavelength dependence of the PL spectra, which are distinctly different from those of commonly observed deep-level emissions associated with the so-called self-activated centers. Moreover, the PL peak energy of the centers depends strongly on the coverage of Se: the longer the time or the higher the flow rate of the Se precursor used for the passivation, the lower the energy of its PL peak. The possible origin of this luminescence is discussed. © 2001 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 3857-3859 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: ZnSe epilayers were grown on GaAs (001) substrates by metal organic chemical vapor phase deposition, using different group VI–II precursor flow ratios. Atomic force microscopy (AFM) examinations of their surface show that epilayers grown with a high VI/II ratio are not as stable as those grown with a low ratio. When exposed to air, Se clusters would appear and grow on the surface of the unstable epilayers. The ripening process could take as long as 50 days at room temperature. Secondary electron and cathodoluminescence images indicate that the clusters are more likely to emerge from areas of high defect density. Moreover, AFM topographic images of epilayers at an intermediate stage of ripening suggest that clusters near surface depressions would grow in size at the expense of others. By using a low accelerating voltage and allowing the clusters to grow to a size larger than the electron interaction volume, we used energy dispersive x-ray analysis to show that the clusters are made up entirely of Se. © 1999 American Institute of Physics.
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  • 7
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optical properties of zincblende structured ZnxCd1−xSe epilayer grown on InP by metal organic chemical vapor phase deposition at temperatures of 360, 400, and 440 °C are investigated with low temperature cathodoluminescence spectroscopy (CL). Both near band gap and deep level emissions are found for the samples grown at 400 °C and above, but deep level emissions are absent for the sample grown at 360 °C. We conclude that the growth temperature should be kept below the temperature at which InP begins to decompose and diffusion of III–V constituents into the epilayer occurs. Evidence of this diffusion comes from an analysis of depth resolved CL studies, which shows that the deep level emissions occur mainly at the epilayer/substrate interface. By monitoring the ratio of the intensity of the deep level emissions to that of the near band emissions, we find that this ratio is larger for samples grown at high temperatures than those at low temperatures. Indium diffusion from the substrate into the epilayer is most likely the source of these deep levels. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
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