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Thermomagnetic and thermoelectric properties of nano and microwires on the basis of Bi semimetal


Author: Para Gheorghe
Degree:doctor of physics and mathematics
Speciality: 01.04.10 - Semiconductors physics and engineering
Year:2012
Scientific advisers: Albina Nikolaeva
doctor habilitat, Institute of the Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova
Pavel Bodiul
doctor habilitat, associate professor (docent), Technical University of Moldova
Institution: Institute of the Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova
Scientific council: DH 02-01.04.10
Institute of Applied Physics, Academy of Sciences of Moldova

Status

The thesis was presented on the 2 October, 2012
Approved by NCAA on the 15 November, 2012

Abstract

Adobe PDF document0.74 Mb / in romanian

Keywords

dimensional effects, nanowires, thermoelectric efficiency, Lifshits’s topological transitions, elastic deformation

Summary

Dissertation contents: introduction, five chapters, general conclusions and recommendations, bibliography – 196 references, 197 pages of the main part, 2 tables and 105 figures.

Number of publications: the obtained results are published in 54 scientific papers and 4 patents.

Research area: low-dimensional structures, nanotechnologies, electronic topological transitions, thermoelectricity.

The aim and objectives of the work: the aim of the current work in the first place has beento obtain single monocrystal nanowires in the glass coverbased on Bi with diameters dnm, in which conditions of dimensional quantization and detection of features of electronic transport in them are realized as well as the research of influence of dimensions on electronic transport and thermoelectric properties. An assessment of possibility to increase thermoelectric efficiency in wires based on semimetals at such external influence as magnetic field, doping, and elastic deformation has been made and recommendations about the use of wires in thermoelectric energy converters of different purposes have been elaborated.

The scientific innovation of the research: for the first time monocrystal Bi nanowires in the glass cover with the diameters dnm, on which manifestation of quantum dimensional effect in dependence of electrical resistance and thermal electromotive force on the temperature, thickness and deformation has been revealed and received. It is experimentally established that by means of doping, elastic elongation and magnetic field it is possible to operate transition ―semiconductor-semimetal‖ and the ratio of electronic and hole contribution in thermal electromotive force in pure and doped by donor and acceptor impurities Bi nanowires, being definding for obtaining n and p-branches of thermoelectric energy converters.

The theoretical value of the research: it has been shown that experimentally observable features of nonmonotonic temperatures dependency of thermal electromotive force α(Т) - sign change and positive polarity extremum and their dependence on diameter of wires d finds a theoretical explanation in the model, considering dimensional quantization effect and electrons scattering on rough - correlated surface. It has been established, that found magnetothermoelectric power "giant oscillations" in aggregate with observable anomalies on deformation dependence of thermal electromotive force attest the existence of the selective interband scattering channel in Bi doped wires at low temperature, that should be considered both in theoretical evaluations and in interpretation of experimental results.

The practical value of the work: for the first time the complex study of thermal electromotive force and resistance of Bi wires dependency on diameters of wires, temperatures, magnetis field, alloying, and elastic extension has been carried out. Power factor (Р.f.) and its dependence on the above-stated parameters in the temperature range 4,2-300К have been calculated that will allow to optimize and recommend Bi wires and its alloys in the glass cover for practical use in thermoelectricity.