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1
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IR Resonant Absorption in Molecular Nanofilms

100%
Pelemiš S., Šetrajčić J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
579-584
EN
The paper presents a theoretical research of changes of optical properties of various nanofilm molecular crystals which are caused by the presence of two parallel and close borders. We used combined analytical-numerical calculation to find the allowed energy states of excitons and their spatial distribution (per layers) along the axis perpendicular to surface planes. We determined permittivity for the observed models of these ultrathin dielectric films and explored the influence of boundary parameters on the occurrence of discrete (per frequencies) and selective (per layers) absorption. The conditions for occurrence of smallest number of resonant absorption lines have been found and their localization has been defined.
2
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Phonon-Induced Thermodynamic Properties of Ultra-narrow Wires

81%
Ilić D., Šetrajčić J., Jaćimovski S.
Acta Physica Polonica A
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2018
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vol. 133
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issue 1
57-62
EN
In this paper, we investigated the influence of size effect on thermodynamic properties of ultra-narrow wires with a simple cubic lattice, by means of two-time dependent Green functions method, adjusted to confined crystalline structures. Poles of Green functions, which defining phonon spectra, are found by solving the secular equation. For different boundary parameters, this problem is presented graphically. The temperature behavior of ultra-narrow wire thermal capacitance is compared to that of bulk structures. It turned out that in low-temperature region thermal capacitance of the ultra-narrow wire is notably lower than in the corresponding bulk sample. How this fact reflects the thermal, conducting and superconducting properties of materials, is discussed in the conclusion.
3
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Phonon Contribution in Thermodynamics and Transport Properties of Ultrathin Ceramic Films

81%
Jaćimovski S., Šetrajčić J., Jaćimovski M., Stojanović V.
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vol. 126
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issue 3
811-820
EN
The dispersion law, density states of phonons, thermodynamics properties and thermal conductivity was analyzed in this paper. It has been shown that at low temperatures, thermal conductivity of thin film is considerably lower that of bulk-structure. It turned out that phonons in thin film require activation energy for exciting. This leads to extremely low specific heat and specific conductivity at low temperatures. Consequences of quoted facts were discussed in detail and their influence on kinetic and thermodynamic properties of thin films is estimated.
4
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Boundary Influence on Permittivity in Molecular Films

81%
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.
5
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Consequences of Confinement Conditions on Absorption in Molecular Nanofilms

71%
Šetrajčić I., Rodić D., Šetrajčić J., Šetrajčić-Tomić A., Vučenović S.
Acta Physica Polonica A
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2018
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vol. 133
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issue 1
129-139
EN
This paper presents a model of molecular ultrathin crystalline film and analysis of dielectric properties of these spatially very restricted structures. Using the two-time dependent Green functions the energy spectrum and possible exciton states were determined and the dynamic permittivity was calculated. It was shown that the appearance of localized states in the boundary layers of the film depend on the thickness and the changing values of parameters in the border areas of the film. These localized states define schedule and determine the number of resonant absorption lines in the infrared area of the external electromagnetic radiation.
6
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Photon's Structure of Motion

61%
Delić N., Tošić B., Šetrajčić J., Markoski B., Pelemiš S., Sajfert V., Zorić V.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
471-475
EN
A free photon Hamiltonian is linearized using Pauli's matrices. Based on the correspondence of Pauli's matrices kinematics and the kinematics of spin operators, it has been proved that a free photon integral of motion is a sum of orbital momentum and spin momentum for a half-one spin. Linearized Hamiltonian represents a bilinear form of products of spin and momentum operators. Unitary transformation of this form results in an equivalent Hamiltonian, which has been analyzed by the method of Green's functions. The evaluated Green function has given possibility for interpretation of photon reflection as a transformation of photon to antiphoton with energy change equal to double energy of photon and for spin change equal to Dirac's constant. Since photon is relativistic quantum object the exact determining of its characteristics is impossible. It is the reason for series of experimental works in which photon orbital momentum, which is not integral of motion, was investigated. The exposed theory was compared to the mentioned experiments and in some elements the satisfactory agreement was found.
7
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Changes in Optical Properties of Molecular Nanostructures

61%
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.
8
Content available remote

Phonon Contribution in Thermodynamics οf Nano-Crystalline Films and Wires

52%
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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