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Документ Effect of deviation from stoichiometry on transport and mechanical properties of Bi2Se3 polycrystals(AIP Publishing, 2021) Menshikova, S. I.; Rogacheva, E. I.The dependences of electrical conductivity, the Hall coefficient, the Seebeck coefficient, thermoelectric power factor and microhardness of Bi2Se3 polycrystals on the degree of deviation from stoichiometry 59.9–60.0 at. % Se and temperature (77–300 K) were obtained. The samples exhibited n-type conductivity in the studied ranges of compositions and temperatures. The boundaries of the Bi2Se3 homogeneity region were estimated. A non-monotonic behavior of the concentration dependences of the properties in the studied composition range, associated with a change in the phase composition and defect structure under the deviation from stoichiometry, was observed. The calculation of the power coefficient in the temperature dependence of electron mobility showed that in a stoichiometric Bi2Se3, electrons are predominantly scattered by acoustic phonons, and under the deviation from stoichiometry the contribution of impurity scattering increases. Based on the experimental data, the Fermi energy EF was calculated in the approximation of the relaxation time and within the framework of the single-band model with a quadratic dispersion law. The obtained values of EF showed that both in stoichiometric and non- stoichiometric Bi2Se3, the conduction is mainly due to electrons in the lower conduction subband.Документ Electrical conductivity and Hall mobility of Bi2Se3 thin films with different thicknesses(Publishing House "UKRPOL" Ltd, 2018) Menshikova, S. I.; Rogacheva, E. I.Документ Quantum oscillations in thickness dependences of transport properties of topological insulator Bi2Se3 thin films(Publishing House SME "Burlaka", 2017) Rogacheva, E. I.; Sipatov, A. Yu.; Menshikova, S. I.Документ Size effects in thin PbTe films(Прикарпатський національний університет імені Василя Стефаника, 2017) Menshikova, S. I.; Rogacheva, E. I.Публікація Size Effects in Transport Properties of PbSe Thin Films(IOP Publishing Ltd, 2016) Rogacheva, E. I.; Nashchekina, O. N.; Menshikova, S. I.Документ Effect of Deviation from Stoichiometry on Thermal Conductivity of Bi2Se3 Polycrystals(Institute of Thermoelectricity National Academy of Sciences of Ukraine, 2020) Menshikova, S. I.; Rogacheva, E. I.The dependences of electronic and lattice thermal conductivity on the composition (59.9 - 60.0) at. % Se of Bi2Se3 polycrystals subjected to a long-term annealing at 650 K. A non-monotonic behavior of these concentration dependences, associated with a change in the phase composition and defect structure under the deviation from stoichiometry, was observed. The boundaries of the Bi2Se3 homogeneity region were estimated. The results of the present work confirm those obtained earlier in our study of the effect of deviation from stoichiometry (59.9 - 60.0 at.% Se) on the electrical conductivity, Hall coefficient, Seebeck coefficient and microhardness of Bi2Se3polycrystals after a similar preparation technology.Публікація Thickness-dependent quantum oscillations of the transport properties in bismuth selenide thin films(Elsevier, 2019) Rogacheva, E. I.; Menshikova, S. I.; Sipatov, A. Yu.; Nashchekina, O. N.The objects of the present study were thin n-Bi2Se3 films with thicknesses d = 10–100 nm, grown by thermal evaporation of n-Bi2Se3 crystals in vacuum onto heated glass substrates. The room temperature d-dependences of the Seebeck coefficient, the Hall coefficient, and the electrical conductivity of the films exhibited an oscillatory behavior, which we attribute to quantum size effects. Such interpretation of the results is supported by the fact that experimentally determined values of the oscillation period are in quite good agreement with the theoretically calculated ones. We suggest that the large amplitude and undamped character of the oscillations in the studied range of thicknesses are connected with the topologically protected gapless surface states of Bi2Se3. The observed oscillatory character of the d-dependences of the transport coefficients should be taken into account when 2D-structures are applied in nanothermoelectricity and other fields of nanoscience and nanotechnology.Документ Dependences of thermoelectric properties on the thickness of thin films of indium doped lead telluride(Institute of Thermoelectricity, 2014) Menshikova, S. I.; Rogacheva, E. I.; Sipatov, A. Yu.; Matychenko, P. V.; Dobrotvorskaya, M. V.Dependences of thermoelectric properties (the Seebeck coefficient S, the electric conductivity σ, the Hall coefficient RH, the carrier mobilityμ and the thermoelectric power P = S²·σ) on the thickness d (d = 10 – 255 nm) of thin films prepared by vacuum evaporation of indiumdoped PbTe crystals and subsequent condensation on (111) BaF₂ substrates were obtained. With decreasing thickness of films to d ≈ 40 nm, there is n- to p-type inversion of conduction which is related to a change in thermodynamic equilibrium conditions and partial reevaporation of lead and/or indium atoms. Extremes were found on the thickness dependences of properties at d₁ ≈ 20 nm which is indicative of hole gas quantization. In the range of thicknesses with n-type conduction there is a smooth change in thermoelectric properties with thickness which testifies to manifestation of classical size effect and is sufficiently well described in the framework of the Fuchs-Sondheimer theory.Документ Size effects in thin n-PbTe films(STC "Institute for Single Crystals", 2015) Menshikova, S. I.; Rogacheva, E. I.; Sipatov, A. Yu.; Zubarev, Evgeniy N.Документ Size effects in chlorine doped PbSe thin films(Institute of Thermoelectricity, 2015) Menshikova, S. I.; Rogacheva, E. I.; Sipatov, A. Yu.; Krivonogov, S. I.; Matychenko, P. V.The possibility of obtaining strongly degenerate (≈ 3·10²⁰ сm⁻³) PbSe thin films (d = 5 – 220 nm) with n-type conductivity by thermal evaporation in vacuum of PbSe crystals doped with PbCl₂, with subsequent condensation onto (001) KCl substrates was established. It was shown that the films had high homogeneity degree, no grain structure was observed. The thickness dependences of thermoelectric properties (the Seebeck coefficient S, the Hall coefficient RH and the electric conductivity σ) of thin films were obtained. In the thickness range d ≈ 5 ÷ 30 nm, oscillation properties were observed with growth of d that are attributable to electron gas quantization. The calculation of S(d) dependence on the assumption of size quantization with regard to contribution of several subbands and the thickness dependence of the Fermi energy was shown to be in agreement with the experimental data. In the region of d > 30 nm there was growth of S and σ with thickness, which is attributable to manifestation of classical size effect and interpreted in the framework of Fuchs-Sondheimer and Mayer theories.