Publications on the project |
014 Excitons and percolation processes in two-phase core-shell SiO2-ZnO structures with a large density of surface nanoclusters |
Authors: | N.V. Bondar, M.S. Brodyn, Y. V. Yermolayeva, M.V. Dobrotvorskaya, A.V. Tolmachev | |
Summary: | The results of an investigation of two-phase media SiO2/ZnO type core/shell with a large density of nanoclusters ZnO at the surface of spherical silica (SiO2) particles are shown. It has been proposed that due to a large surface energy of the SiO2, a nanoclusters growth like the quantum disks with the diameter of ZnO about 10 nm and at heights up to the exciton Bohr radius that was estimated using the effective-mass method and very well conforming to experimental results. For the first time to shown that the photoluminescence spectrum of this structures can be caused of the phase percolation transition of carriers at the spherical surface of SiO2 that are consequences of a large density of ZnO-nanoclusters. This leads to an interaction of the latter, but in contrast to 3D, here the size effect of excitons are not disappears. The wave function of excitons, as a result of a large density of SiO2, is the large-size that leads to the appearance of the deeper states due to of oxygen vacancies (VO), VO complexes, Zn interstitial-related complexes. | |
Keywords: | exciton, quantum dot, SiO2, ZnO, percolation | |
Edition: | Ukr. J. Phys | | | 2010,
1035 - 41,Ukrainian |
014 Fractal manifestation of percolation-cluster structural element in emmision spectra of sample with ZnSe quantum dots. |
Authors: | N.V. Bondar | |
Summary: | For the first time, on a basis of results of researches samples with ZnSe quantum dots in the dielectric matrix at the concentration beyond and above of the percolation threshold reveals the effect of different of structures elements the percolation cluster, as to the backbone and dangling ends, and inside voids on the shape of emission spectra of samples. At a qualitative level shown those even structures elements of clusters are formed owns of excitonic states energy which depends on an amount of nearest-neighbors in the backbone and dangling ends. As a result excitonic states are delivered to energies and may be observed in the experiment. | |
Keywords: | exciton, percolation, quantum dot, ZnSe | |
Edition: | Ukr. J. Phys | | | 2011,
988 - 992,Ukrainian |
014 Free and bound states of excitons in percolation cluster of ZnSe quantum dots in dielectric matrix |
Authors: | N.V. Bondar and M.S. Brodyn | |
Summary: | Two-phase systems (borosilicate glasses with ZnSe
quantum dots) were studied. The results obtained provided an insight both into the mechanism of the formation of a phase percolation transition of excitons in the array of quantum dots at the critical concentration and radii and the contribution ofdielectric mismatch between ZnSe and matrix to the transition. Using the above two-phase system as an example, it was found for the first time that such a complex fractal object as the percolation cluster of quantum dots had not only free (mobile) states but bound (immobile) ones well.
This bound (immobile) states resemble the type-II excitons in superlattices or the impurity states in bulk semiconductors. It is shown that the polarization of the two-phase system interface is the main source of these immobile states whose energy is dependent on size of quantum dots and their average separation. | |
Keywords: | percolation; quantum dots; ZnSe; excitons. | |
Edition: | Low Temperature Physics | | | 2011,
1288 - 1294,Russian |
014 Evolution of excitonic states in two-phase systems with quantum dots of |
Authors: | N.V. Bondar, M.S. Brodyn | |
Summary: | In two-phase disordered media composed of borosilicate glass with ZnSe or CdS quantum dots, the
formation of a phase percolation transition of carriers for near-threshold concentrations that are
manifested in optical spectra has been observed. Microscopic fluctuations of the quantum-dot density
near the percolation threshold were found that resembled the phenomenon of critical opalescence,
where similar fluctuations of the density of a pure substance appear near to a phase transition. It is
proposed that the dielectric mismatch between a matrix and ZnSe or CdS quantum dots plays a
significant role in the carrier (exciton) delocalization, resulting in the appearance of a ‘‘dielectric
Coulomb trap’’ beyond the QD border and the formation of surface states of excitons. The spatial
overlapping of excitonic states at the critical density of quantum dots results in a tunneling of carriers
and the formation of a phase percolation transition in such media | |
Keywords: | Quantum dots
Percolation
Excitons | |
Edition: | Physica E | | | 2010,
1549 - 1554,English |
014 Emission and percolation of excitons in dense sensembles of quantum dots on the spherical surface |
Authors: | N.V. Bondar, M.S. Brodyn, Yu.V. Yermolayeva, A.V. Tolmachev | |
Summary: | We study core/shell heterostructures in which a core (SiO2) is overcoated with a shell of ZnO quantum
dots, randomly distributed on the sphere surface with the surface filling factorP0.45. Due to the high
surface energy of SiO2spheres, ZnO quantum dots have the shape of disks in which, in spite of the large
radii, quantum size effects of excitons are retained. The height of ZnO disks estimated by the effective
mass approximation is comparable with the exciton diameter in bulk ZnO. Analysis of optical spectra
has shown that, at the given density of ZnO quantum dots, the exciton system is above the percolation
threshold. The quantitative parameters characterizing such phenomenon are obtained using the
elements of percolation theory and the topology of the samples. | |
Keywords: | percolation; quantum dots; ZnSe; excitons. | |
Edition: | Physica E | | | 2011,
1882- 1886,English |
014 Percolation and luminescence of excitons in two-phase structures of SiO2/ZnO with a large density and random distribution of quantum dots on the spherical surface |
Authors: | N.V. Bondar | |
Summary: | The findings of investigation into of structures are
defined as the nanospheres silica (SiO2) particles with ZnO
quantum dots which is randomly distributed over their surfaces,
and are covered about 45% their of the area are shown. Due to
of the large surface energy of spheres, ZnO quantum dots are in
the form of the quantum dicks in which is preserved of quantum
effect in spite of their the large radii. By the effective-mass method
is calculated the height dicks that is comparable with an exciton
diameter of the bulk ZnO. The analyses of optical spectra shown
that at given of the covering area of spheres, excitons in array
of quantum dots are above the percolation threshold. The use of
elements of the percolation theory and topology of samples allow to have reseived of the quantitative parameters which are defined this an phenomenon. | |
Keywords: | | |
Edition: | | | | 2011,
481 - 487,Russian |
014 Photoluminescence and energy of excitons in the percolation cluster of ZnSe quantum dots as a fractal object |
Authors: | N.V. Bondar, M.S. Brodyn | |
Summary: | The results of studies of samples with ZnSe quantum dots with a density corresponds-sponding exciton percolation threshold, and much higher than it when the quantum dots form
conglomerates. For the first time detected the radiation exciton percolation cluster of coupled quantum
points as a fractal object. Analysis of the structure of the photoluminescence spectra of the samples showed
they are determined by the contribution of the exciton states located in different structural elements
percolation cluster, such as the skeleton (backbone), dead ends and inner emptiness. A
qualitative model explaining the dependence of the energy of excitons in these structural elements of the
the concentration of quantum dots in a matrix | |
Keywords: | percolation; quantum dots; ZnSe; excitons. | |
Edition: | Semiconductors | | | 2012,
644 - 648,Russian |
014 Education connectivity (percolation) of excitons in solid and sparse arrays of quantum dots in a matrix different topologies |
Authors: | N.V. Bondar, M.S. Brodyn, Yu.V. Yermolayeva | |
Summary: | In the first part, a given reports provides an explanation of some differences
between the geometrical and quantum percolations of the charge carriers or
excitons in dense and diluted ensembles of quantum dots, which were synthesized within the 3D-matrix
or over the spherical surface. Differences in experimental methods
of registration of the percolation threshold of excitons
within the 3D-matrixes with the metal
or semiconductor contaminations are
shown. In the second part, results are shown, which confirm that, for structures with the ZnO or CdS quantum dots grown at the spherical surface of
SiO
2
, there are two critical concentrations or two percolation thresholds.
Such phenomenon is similar to another one, which has been observed in the
ionic conductors containing the dielectric-phase inclusions. Based on obtained results, the explanation of nature of this phenomenon is provided. | |
Keywords: | II - VI semiconductors, quantum dots, exciton percolation | |
Edition: | Nanosystems, Nanomaterials, Nanotechnologies | | | 2013,
579 - 594,Russian |
014 The optical properties of the monodisperse nanoparticles Y2O3-ZnO spherical shape |
Authors: | A. N. Gruzintsev, N. A. Dulina, G. A. Emel’chenko, Yu. V. Ermolaeva, E. A. Kudrenkoc, A. V. Tolmachev | |
Summary: | On the basis of the developed method of synthesis of mesoporous spherical particles with a dispersion of yttria
sizes in the range of 10-15% and infiltration techniques have active components sphere-synthesized nanocrystalline particles trical composition Y2O3-ZnO. The structure, the analysis of the spectra diffuse reflectance and photoluminescence geterochastits and stimulated emission of excitons
zinc oxide in the nanocomposite after annealing at various temperatures. The formation ZnO nanocrystals within the pores of the spheres Y2O3 during synthesis of the material with a single procedure infiltration. The laser effect is associated with a change in the effective refractive index and local
photon density of states in the phosphor nanoparticles optical resonators spherical shape | |
Keywords: | templates, ZnO, SiO2, nanoparticle, Y2O3-ZnO | |
Edition: | Physics of the Solid State | | | 2012,
2125 - 2130,Russian |
The events in the framework of the project |
|
014 Executant:Institute of Physics, Department of Physics and Astronomy, Section Physical, Engineering and Mathematics 1.2. Physics of semiconductor nanostructures Purpose:The central optical properties, the energy spectrum of carriers (excitons) and their of tunneling processes in the semiconductor nanodimensional objects of type "core/shell" C1@C2 (С1 = SiO2, C2 = ZnO, CdS, ZnSe, ZnS et al.) to attack and the physical processes that form the basis of a forming of theses strutures. Expected results:Release of new product: technology Stage 1:Research methods of spectroscopy physical mechanisms of the formation and growth of nanoparticles II - VI semiconductors (ZnO, CdS, ZnSe, ZnS and activated rare earth oxides) on the spherical surface template SiO2. Stage 2:Investigation of the structure, morphology and density arrangement of nanoparticles on the surface of spherical template SiO2, study the effect of surface curvature templates on the morphology and structure of nanoparticles and determining the optimal values of these parameters for making quality films or three-dimensional photonic crystals. Stage 3:Research spectral methods, at different temperatures, electron and exciton processes in the obtained nanoparticles, to develop process models exciton relaxation in a topological space other than plane or volume. Stage 4:Research carriers tunneling processes on the surface of silica spheres depending on the density of nanoparticles, their shape and material parameters of the surrounding environment. Stage 5:Studies of the formation of percolation phase transition of charge carriers (excitons) and its manifestation in optical spectra of the samples.
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