KEYWORDS: Particles, Absorption, Dielectrics, Optical spheres, Optical properties, Optical spectroscopy, Near field optics, Near field scanning optical microscopy, Solids, Satellites
Solving the self-consistent volume integral equation, we compute the local susceptibilty, as well as volume-averaged one of a small parallelepipedal particle interacing with a flat substrate. To estimate the measure of nonpointness of a particle, the susceptibility in the particle center is compared with that calculated in the dipole point-like approximation. It is shown that a parameter specifying nonpointness is determined by the difference in the particle and ambient dielectric constant, as well as by measure of deviation of the particle shape from cubic one. Numerical calculations of absorption cross-section carried out for small dielectric particles shw that the substrate effects lead to the low-frequency shift of the spectra and appearance of a low-frequency subsidiary peak.
Granular gold and nickel films were prepared by thermal vacuum deposition onto glass substrates. Optical transmittance at near-normal incidence was recorded as a function of the relative mass thickness on each side of the percolation threshold. We show that our transmittance spectra may be described within the framework of Bruggeman's symmetrical approximation for the effective dielectric function with some modifications.
For composite media some recent phenomenological approaches to treating dielectric properties in the long-wavelength limit are considered. Among the problems discussed are the features of media with close-packed particles, role of topology and bounds for the effective dielectric function. As an example, we consider close packing of submicron TiO2 particles. An analysis of the near-normal reflection spectra is made. Using the Kramers-Kronig relation and the modified Avary method, we obtained a composite dielectric function in far IR. When modeling the dielectric properties of the system studied, we used Bergman's representation.
The features of the infrared reflection spectroscopy are considered for long-period semiconductor superlattices. Taking the GaAs/GaPxAs1-x superlattice system as an example, the applicability of the bulk model is related to light penetration/localization depths. We propose to use relative measurements (i.e. to study RpRs spectra) for raising the accuracy of determination of superlattice parameters by solving the inverse problem.
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