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1
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Raman Scattering from Acoustic Phonons Confined in Spherical Nanoparticles

100%
Kostić R.
Acta Physica Polonica A
|
2009
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vol. 116
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issue 1
62-64
EN
Low-frequency Raman scattering from small spherical particles is analyzed. Frequencies of vibrational modes are calculated in elastic continuum approximation, which considers one nanoparticle as homogeneous elastic sphere. Parameters of this model are transverse (v_T) and longitudinal (v_L) sound velocities of material, i.e. elastic properties of bulk material. Frequencies of vibrational modes are scaled as function of mentioned bulk parameters for symmetric l=0 and quadrupolar l=2 spheroidal modes, in the case of stress-free boundary conditions. Calculated values are compared with the low-frequency Raman experimental results from literature (Ge, Si, CdS, CdSe, CeO_2, ...). These calculated relations can be practically used to examine nanoparticles of any bulk material. We presented also a procedure how to establish v_L and v_T of material from low-frequency Raman spectra and dimension d of particles.
2
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Electron and Hole States in Closed Spherical Quantum Dot with Linearly Graded Composition

64%
Kostić R., Stojanović D.
Acta Physica Polonica A
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2009
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vol. 115
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issue 4
768-770
EN
The theoretical investigation of the electron and hole spectra in a quantum dot with a linearly graded composition within the effective mass approximation is presented. The particular example is β-HgS surrounded by CdS. β-HgS core of radius r_C is surrounded by concentric spherical layers each of Hg_{1-x}Cd_{x}S composition (x is function of r) and finally, form radius r_S by CdS. The existence of these intermediate layers, as model of graded composition, influences rapidly electron and hole spectra.
3
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Multi-Color Emission in Quantum-Dot-Quantum-Well Semiconductor Heteronanocrystals

64%
Kostić R., Stojanović D.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
598-602
EN
We present calculation results of multi-color spontaneous emission from quantum-dot-quantum-well semiconductor heteronanocrystals. Our theoretical results explain experimental results of onion-like spherical system similar to: CdSe (core), ZnS (shell), CdSe (shell) spherical quantum dots surrounded by ZnS. We demonstrate influence of shell thickness to exciton localization in distinct layers of heteronanocrystals. Multi-color emission of such heterosystem is determined by l=0, n=1 state localization in CdSe core and by l=0, n=2 state localization in CdSe shell.
4
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Binding Energy of the Hydrogenic Impurity in CdTe/ZnTe Spherical Quantum Dot

64%
Stojanović D., Kostić R.
Acta Physica Polonica A
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2011
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vol. 120
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issue 2
234-237
EN
Binding energy of a hydrogenic impurity located at the center of the CdTe/ZnTe spherical quantum dot has been calculated under the effective mass approximation by solving Schrödinger equation analytically. Eigen energies are expressed in terms of the Whittaker function and Coulomb wave function. The results show that impurity binding energy strongly depends on QD size if it is around one effective Bohr radius.
5
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Quasistationary Electron States for CdTe/ZnTe/CdTe Open Spherical Quantum Dots

64%
Stojanović D., Kostić R.
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issue 5
768-771
EN
The energy spectra of an electron in open spherical quantum dot (QD) within the effective mass approximation (EMA) and rectangular potential model is presented. Energy structure of quantum dots is important because of their possible applications in electronic and optoelectronic devices. For proper description and interpretation of tunneling processes knowledge of resonant states of quantum dots is necessary. Energy values depend on parameter like size of system and spatial composition. The lifetimes of the quasistationary states are computed within the framework of the scattering S-matrix method. It is shown how core radius and barrier thickness for the CdTe/ZnTe/CdTe example influence electron states and their lifetimes.
6
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Resonant Raman Spectra of CdTe/ZnTe Self Assembled Quantum Dots

39%
Romčević N., Romčević M., Kostić R., Stojanović D., Abolmasov B., Karczewski G., Galazka R.
Acta Physica Polonica A
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2009
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vol. 116
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issue 1
88-90
EN
In this paper we present Raman scattering and photoluminescence spectra measured on CdTe/ZnTe self assembled quantum dots. The photoluminescence spectrum has shown two main emission peaks, both connected with existing of quantum dots. One presents direct deexcitation to ground state and the other is optical phonon (οmega = 207.3 cm^{-1})-assisted deexcitation. The registered multiphonon emission process depends on temperature. At low temperature phonon spectra shows line at 450 cm^{-1} (TA + 2LO in ZnTe) and 595 cm^{-1} (2LO + TO(Γ) in ZnTe).
7
Content available remote

Optical Characterization of Graphene and Highly Oriented Pyrolytic Graphite

39%
Kostić R., Mirić M., Radić T., Radović M., Gajić R., Popović Z.
Acta Physica Polonica A
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2009
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vol. 116
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issue 4
718-721
EN
We present a symmetry analysis of allowed infrared and Raman modes in graphene and highly oriented pyrolytic graphite. Surface structure for highly oriented pyrolytic graphite is examined using atomic force microscopy. As experimental tools, we used infrared spectroscopic ellipsometry in order to investigate the pseudodielectric function of highly oriented pyrolytic graphite in the mid-infrared range (500-7000 cm^{-1}) and Raman spectroscopy to investigate the influence of layers number decrease. As a result, we propose a method for an experimental verification of graphene.
8
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Raman Scattering from ZnO(Fe) Nanoparticles

33%
Romčević N., Kostić R., Romčević M., Hadžić B., Kuryliszyn-Kudelska I., Dobrowolski W., Narkiewicz U., Sibera D.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1323-1328
EN
Nanocrystalline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine composition of the samples (ZnO, Fe₂O₃, ZnFe₂O₄) and the mean crystalline size (8-52 nm). In this paper we report the experimental spectra of the Raman scattering (from 200 to 1600 cm¯¹). Main characteristics of experimental Raman spectrum in 200 to 1600 cm¯¹ spectral region are: sharp peak at 436 cm¯¹ and broad two-phonon structure at ≈ 1150 cm¯¹, typical of ZnO;broad structure below 700 cm¯¹ that has different position and shape in case of ZnFe₂O₄ or Fe₂O₃ nanoparticles.
9
Content available remote

Low-Frequency Raman Scattering from ZnO(Fe) Nanoparticles

33%
Kostić R., Romčević N., Romčević M., Hadžić B., Rudolf R., Kuryliszyn-Kudelska I., Dobrowolski W., Narkiewicz U., Sibera D.
Acta Physica Polonica A
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2009
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vol. 116
|
issue 1
65-67
EN
Nanocrystalline samples of ZnO(Fe) were synthesized by wet chemical method. Samples were characterized by X-ray diffraction to determine the sample composition and the mean crystalline size. Low-frequency Raman modes were measured and assigned according to confined acoustic vibrations of spherical nanoparticles. Frequencies of these vibrational modes were analyzed in elastic continuum aproximation, which considers nanoparticle as homogeneous elastic sphere.
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