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Boundary Influence on Permittivity in Molecular Films

100%
Vučenović S., Šetrajčić J., Mirjanić D., Škipina B.
Acta Physica Polonica A
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2007
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vol. 112
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issue 5
963-968
EN
A microscopic theory of optical properties of thin molecular films, i.e. quasi 2D systems bounded by two surfaces parallel to XY planes was formulated. Harmonic exciton states were calculated using the method of two-time, retarded, temperature dependent Green's functions. It was shown that two types of excitations can occur: bulk and surface exciton states. Analysis of the optical properties (i.e. dielectrical permittivity) of these crystalline systems for low exciton concentration shows that the permittivity strongly depends on boundary parameters and the thickness of the film. Influences of boundary conditions on optical characteristics of these nanostructures were especially analyzed.
2
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Changes in Optical Properties of Molecular Nanostructures

76%
Vučenović S., Šetrajčić J., Markoski B., Mirjanić D., Pelemiš S., Škipina B.
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issue 5
764-767
EN
This paper represents an overview about exciton systems in the molecular nanostructures (ultra thin films and superlattices) and their implications on optical properties, primarily on absorption coefficient, which is given in the form of dielectric permittivity. With utilization of Green's function method, we have calculated dispersion law, spectral weight of exciton states and dielectric permittivity for every type of nanostructures. All obtained results are compared with optical properties in bulk crystals. Dielectric permittivity in all types of nanostructures shows very narrow and discrete dependence of external electromagnetic field frequency, which is a consequence of the expressed quantum effects, very thin thickness in these structures (or at least one dimension confinement) and boundary conditions.
3
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Phonon Contribution in Thermodynamics οf Nano-Crystalline Films and Wires

64%
Šetrajčić J., Mirjanić D., Vučenović S., Ilić D., Markoski B., Jaćimovski S., Sajfert V., Zorić V.
Acta Physica Polonica A
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2009
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vol. 115
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issue 4
778-782
EN
Spectra of possible phonon states, as well as thermodynamic characteristics of nanocrystals (ultrathin film and quantum wire) of simple cubic crystalline structure are analyzed in this paper, using the method of two-time dependent Green functions. From energy spectra and internal energy of the system the thermal capacitance of these structures in low temperature region is found. The temperature behavior of specific heat is compared to that of corresponding bulk structure. It is shown that at extremely low temperatures thermal capacitance of quantum wire is considerably lower than the thermal capacitance of film as well as the bulk sample. Consequences of this fact are discussed in detail and its influence to thermodynamic properties of materials is estimated.
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