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Information × Registration Number 0218U001267, 0115U000515 , R & D reports Title The influence of surface metal layers on the thermoelectric properties of crystals, thin films and nanocomposite structures 3D-topological insulators popup.stage_title Head Rogacheva Elena, Доктор фізико-математичних наук Registration Date 22-02-2018 Organization The Kharkov state polytechnical university popup.description2 Objects of the research: the pecularities of transport phenomena and thermoelectric properties in crystalline samples and nanostructures of 3D topological insulators attributed to presence of metallic surface layer. Goal of the work: to reveal the peculiarities of thermoelectric transport in bulk crystals and thin films based on IV-VI (PbTe, PbSe, SnTe), V2VI3 (Bi2Te3, Bi2Se3) semiconductor compounds and Bi-Sb solid solutions attributed to the presence of metallic surface layer. Research methods: measurement conductivity, Hall coefficient and the Seebeck coefficient in the temperature range 77 - 300 K Results - The nature of dependencies of the kinetic coefficients on the thin films thickness of Bi2Te3, Bi2Se3, Sb2Te3 compounds with n- and p-type conductivity and Bi-Sb solid solutions was established. The temperature dependencies of the kinetic coefficients for films of the Bi2Te3, Bi2Se3, Sb2Te3 compounds, and Bi-Sb solid solutions of various thicknesses were obtained. The oscillatory behavior of the dependencies of the kinetic coefficients on the thin films thickness was revealed. Such oscillations were attributed to the manifestation of quantum size effect. The correspondence between the oscillation periods observed experimentally and the results of the theoretical calculation within the framework of the infinitely deep potential well model was obtained. The features of the thickness dependencies of the properties (significant amplitude and undamped character of oscillations) were attributed to the change of conditions at the quantum well boundaries due to the presence of a topological layer that protects surface states from scatering on time-reversal symmetry defects, which is known to be one of the fundamental properties of topological insulators. The manifestation of the classical size effect in thin films of IV-VI, V2VI3 compounds and Bi-Sb solid solutions was revealed and was interpreted within the framework of the Fuchs-Sondheimer theory. Novelty - the features of thickness and temperature dependences of thermoelectric properties were revealed. It was caused by the fact that the investigated materials belong to the class of topological insulators. Theoretical interpretation of the obtained experimental results is carried out within the framework of modern concepts of nanophysics on quantum size effects and topological insulators. Practical value - The new method of growing high-quality thin films by thermal evaporation in a vacuum of crystals with subsequent condensation on glass and mica substrates was developed. It was shown that there is a nonmonotonic dependence of the kinetic coefficients on the thickness of thin films of V2VI3, IV-VI compounds and Bi-Sb solid solutions, which indicates the possibility of controlling thermoelectric properties by varying the films thickness. The obtained dependences of the kinetic properties on the thickness should be taken into account in the development of thin-film thermoelectric materials with n- and p-types of conductivity and low-dimensional converters with high efficiency. Product Description popup.authors Будник Олександр Валентинович Водоріз Ольга Станіславівна Дорошенко Ганна миколаївна Дроздова Ганна Анатоліївна Мартинова Катерина Вікторівна Меньшикова Світлана Іванівна Ніколаєнко Ганна Олександрівна Орлова Дар'я Сергіївна Рогачова Олена Іванівна popup.nrat_date 2020-04-02 Close