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  • 78.30  (3)
  • 1
    ISSN: 1432-0630
    Keywords: 78.40 ; 78.30 ; 73.60 ; 78.65
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Optical properties in the spectral range from 0.06 to 5.5 eV of fullerite films on different substrates, C60 powder, and dissolved fullerene material are investigated by spectroscopic ellipsometry and optical transmission and reflection measurements. Depolarization effects are taken into account during determination of the dielectric function of fullerite films by ellipsometry. The optical gap for C60 films is found to be 1.63 eV. Three optical absorption bands are observed at 2.69, 3.53, and 4.49 eV. The dielectric function in the infrared shows the four characteristic infrared vibrational modes. The interference pattern seen in UV/VIS reflection measurements are used for high-precision thickness determination of the films. The Clausius-Mossotti formula is successfully applied to reproduce the experimental optical data measured in C60/dichlormethane solutions. Deviations between theory and experiments provide interesting information about the intermolecular interaction of the C60 molecules. A tentative interpretation of the measured absorption bands is presented.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-6079
    Keywords: 42.20 ; 78.30
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper investigates the dielectric properties of inhomogeneous samples consisting of small alkali halide particles (NaCl, KBr) on gold-coated substrates. Our reflection measurements in the far infrared can be simulated as a thin layer of the powder with an effective dielectric function on a perfectly reflecting substrate. Scanning electron micrographs provide useful information about sample topology. Several mixing formulas (e.g. the Maxwell-Garnett, the Bruggeman- and the Looyenga-formula) lead to effective dielectric functions neglecting the individual arrangement of the particles. The essence of our work is that, in contrast, the general ansatz of the Bergman spectral representation has to be employed in order to take into account topology effects on the dielectric function based on the so-called spectral densityg adjustable to the specific situation.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1434-6079
    Keywords: 42.20 ; 78.30
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Measurements of the optical constants of metal-insulator composites in the far infrared provide information about the dielectric functions (DF) of the components and about the electromagnetic interaction of the different grains. If the metal particles — and their separations — are much smaller than the wavelength of the light, the sample can be characterized in terms of an effective dielectric function. The Bergman representation of the effective dielectric function takes into account the dielectric properties of the metal and of the host material as well as the interaction of the grains. The so-called spectral density occuring in the Bergman representation describes the influence of the sample microstructure, which is important for the correct description of the interaction between the grains. A variety of simple mixing formulae — each reflecting a specific microgeometry — have been published, e. g. the Maxwell-Garnett formula, the Looyenga formula or the Bruggeman formula. They all are special cases of the Bergman representation with their own spectral densities depending only on the metal volume fraction. From the knowledge of the fundamental Bergman representation we analyze the applicability of these simple formulae to metal-insulator systems. Their use may lead to severe misinterpretation of experimental data, because the specific microtopology is not accounted for in the right way. We show this for a cermet of Pt spheres in Al2O3 comparing our measurements with calculations on the basis of the simple mixing formulae. It is demonstrated that the measured effective DF is consistent with the Bergman representation by an adjustment of a spectral density to the experimental data. We propose a procedure for the extraction of the DF of one of the constituents from experimental data.
    Type of Medium: Electronic Resource
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