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1
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On Number of Exciton Surface States in Multilayer Molecular Slabs

100%
An N. B.
Acta Physica Polonica A
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1997
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vol. 92
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issue 6
1197-1208
EN
Criteria for the possible number of exciton surface states in a multilayer molecular slab are elucidated in detail. Namely, we explicitly determine the domains of system parameters where the size dependence plays a role. We further clarify the way a surface state is localized in the slab in both asymmetric and symmetric configurations. Basing on our results which are obtained within the first nearest layer approximation, we also conjecture properties to be expected when further nearest layers are taken into consideration.
2
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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.
3
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Physics of Neutral-to-Ionic Phase Transition in Organic Charge Transfer Semiconducting Compounds

100%
Cailleau H., Lemée-Cailleau M. H., Le Cointe M., Luty T.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
597-608
EN
An uncommon excitonic instability takes place in some exotic semiconducting compounds. Indeed, the equilibrium neutral-to-ionic (N-I) phase transition, as well as the non-equilibrium photo-induced phase transformation, observed in some organic charge-transfer complexes, originate from intra- and inter-chain cooperative effects between structurally relaxed charge-transfer excitations. This electronic-structural phase transition manifests itself by a change of the degree of charge-transfer and a dimerization distortion with the formation of donor-acceptor pairs along the stacking axis in the I phase. Thermal charge-transfer excitations associated with the formation of I strings along N chains are at the heart of the mechanism of this phase transition. These relaxed electronic excitations, which are an intrinsic feature of low-dimensional systems with strong electron-phonon coupling, can be described in terms of self-trapping and self-multiplication of charge-transfer excitons. Precise structural studies on the prototype compound, tetrathiafulvalene-p-chloranil allow to highlight the respective role taken by the ionicity and the dimerization. Symmetry and thermodynamics analysis of the N-I transition, based on recent determination of the pressure-temperature phase diagram, make possible to present a consistent picture of this phase transition. Supported by theoretical considerations taking into account the interplay between quantum and thermal effects, the experimental observations show that the N-I transition results from the condensation and the ordering (crystallization) of charge-transfer excitations, following a phase diagram analogous to the solid-liquid-gas one.
4
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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.
5
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Consequences of Confinement Conditions on Absorption in Molecular Nanofilms

75%
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.
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