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Nova Odesa, Ukraine

Ozcan N.,University of Helsinki | Kortelainen T.,Tampere University of Technology | Golovanov V.,South Ukrainian University | Rantala T.T.,Tampere University of Technology | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

We present density-functional theory calculations of the electron spin resonance g and hyperfine coupling A tensors in cluster models of a positively charged oxygen vacancy VO + in semiconducting tin dioxide, SnO2. Convergence of the results with the cluster size, basis set, choice of exchange-correlation functional, and choice of the method of the cluster termination by either pseudohydrogen atoms or electrostatic embedding, are investigated. The results agree with two of the earlier experimental assignments of the g value around 2.00, whereas in the case of other experiments (g=1.89), a reassignment is suggested. We also investigate the energy levels of the impurity states via the Kohn-Sham orbital energies of the defect-free bulk, positively charged vacancy (VO +), and neutral vacancy (VO 0) structures. © 2010 The American Physical Society. Source


Ivanovskaya M.,Belarusian State University | Ovodok E.,Belarusian State University | Golovanov V.,South Ukrainian University
Chemical Physics | Year: 2015

Abstract The nature of paramagnetic centers which are responsible for the EPR signal at g = 1.8-1.9 in tin (IV) oxide was studied. Polycrystalline SnO2 samples were obtained by sol-gel method and by thermal treatment of the precursors containing tin atoms in different oxidation states. The parameters of the EPR spectra recorded after heat treatment of the samples in air, oxygen and hydrogen atmospheres, and in vacuum were analyzed. The observed parameters of the EPR spectra do not allow to assign the paramagnetic center with g = 1.8-1.9 to Sn3+ center. The structure of the paramagnetic center attributed to the EPR signal at g = 1.8-1.9 was proposed. The proposed structure of the paramagnetic center includes a complex of oxygen vacancies at (1 0 1) plane of rutile-type SnO2 lattice. © 2015 Elsevier B.V. Source


Golovanov V.,Tampere University of Technology | Golovanov V.,South Ukrainian University | Golovanova V.,South Ukrainian University | Kuisma M.,Tampere University of Technology | Rantala T.T.,Tampere University of Technology
Journal of Applied Physics | Year: 2013

The spin Hamiltonian parameters of intrinsic defects in tin dioxide (SnO2) doped with fluorine or hydrogen are examined through the first-principles electronic structure calculations based on density functional theory (DFT). The electron paramagnetic resonance signals with g-tensor value in the range of 1.89-1.94 were found for tin vacancy (VSn) and its complex with oxygen vacancy (VSn-VO) associated with a donor like interstitial hydrogen or fluorine, substituting oxygen. The calculated parameters are consistent with experimental observations, which indicate that Sn vacancies may be present in SnO2 at essentially higher concentration than it is predicted by DFT based on the formation energies calculations. Within the second coordination shell of the tin vacancy, the VO may stabilize in the singly ionized charge state, which is otherwise considered to be unstable for isolated oxygen vacancy in the bulk of SnO2. © 2013 AIP Publishing LLC. Source


Golovanov V.,South Ukrainian University | Golovanov V.,Tampere University of Technology | Golovanova V.,South Ukrainian University | Rantala T.T.,Tampere University of Technology
Journal of Physics and Chemistry of Solids | Year: 2016

First-principles density functional theory calculations in the generalized gradient approximation, with plane wave basis set and pseudopotentials, have been used to investigate the desorption pathways of molecular oxygen species adsorbed on the SnO2 (110) surface. Energetics of the thermodynamically favored precursors is studied in dependence on the surface charge provided either by surface defects or by donor type impurities from the near-surface region. The resonant desorption modes of O2 molecules are examined in the framework of ab initio atomic thermodynamics and relationship of these results to experimental observations is discussed. © 2015 Elsevier Ltd. Source


Golovanov V.,Tampere University of Technology | Golovanov V.,South Ukrainian University | Viitala M.,Tampere University of Technology | Kortelainen T.,Tampere University of Technology | And 2 more authors.
Surface Science | Year: 2010

Siloxane is a favorable candidate as an anchor group that can be used to bind organic molecules to SnO2 surfaces, with a wide range of practical applications. Therefore, adsorption geometries and energies of siloxane coupler on the SnO2 (110) surface have been investigated in this study using quantum-chemical periodic density functional theory (DFT) calculations. We present a comparative study of different siloxane adsorption arrangements on pristine and fluorine doped SnO2 surface. According to the calculations, the surface doping with fluorine leads to stabilization of the siloxane network at the stannic oxide surface. The trend is analyzed in terms of additional charge provided by F impurities to the chemisorbed oxygen atoms thus increasing the ionicity of their bonding. Implications of the current findings for the design of organicmetal oxide interface with better thermo-stability and improved electronic properties are discussed. © 2010 Elsevier B.V. All rights reserved. Source

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