Dirac states and thermoelectric properties, topological insulators bi2te3 wires and layers
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NIKOLAEVA, Albina, KONOPKO, Leonid, ROGACKI, Krzysztof, HUBER, Tito, GHERGISHAN, Igor, BOTNARY, Oxana. Dirac states and thermoelectric properties, topological insulators bi2te3 wires and layers. In: Materials Science and Condensed Matter Physics, Ed. 9, 25-28 septembrie 2018, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2018, Ediția 9, p. 212.
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Materials Science and Condensed Matter Physics
Ediția 9, 2018
Conferința "International Conference on Materials Science and Condensed Matter Physics"
9, Chișinău, Moldova, 25-28 septembrie 2018

Dirac states and thermoelectric properties, topological insulators bi2te3 wires and layers

CZU: 537.9+538.9

Pag. 212-212

Nikolaeva Albina1, Konopko Leonid1, Rogacki Krzysztof2, Huber Tito3, Ghergishan Igor1, Botnary Oxana1
 
1 Institute of the Electronic Engineering and Nanotechnologies "D. Ghitu",
2 Institute of Low Temperatures and Structural Research, PAS,
3 Howard University
 
Proiecte:
 
Disponibil în IBN: 8 februarie 2019


Rezumat

In this paper, we present a study of Shubnikov de Haas (SdH) oscillations at 4.2 and 2.1 K and temperature dependences of thermopower α(T) and resistivity ρ(T) for layers and wires based on Bi2Te3 topological insulators (TIs) in a range of 4.2–300 K.  Single-crystal Bi2Te3 layers of n- and p-type with a thickness of 10–30 μm were prepared by the mechanical exfoliation of layers from a bulk single-crystal ingot of a similar composition using a scotch tape. The mechanical exfoliation mostly results in breaking the Te(1) - Te(1) van der Waals bond and the formation of few-quintuples layers. The X-ray diffraction studies revealed that the layers had a single-crystal structure; the cleavage plane of the layers was perpendicular to the C3 trigonal axis. Glass-insulated Bi2Te3 microwires were prepared by the Ulitovsky–Taylor method [1]; in general, the microwire core had a polycristalline structure consisting of large disoriented single-crystal blocks.  High quantum mobilities μg~2*104 cm2/V*s were determined from SdH oscillations in longitudinal (HïïI) and transverse (HI) magnetic fields of up to 14 T at 4.2–2.1 K; the mobilities are substantially higher than those in bulk Bi2Te3 samples of the same composition.  A phase shift in SdH oscillations in longitudinal (HïïI) and transverse (HI) magnetic fields was found at H→ꝏ, which is characteristic of the Dirac state of TIs at the surface [2].  Analysis of the experimental data on the temperature dependences of resistivity ρ(T) and thermopower α(T) in layers and wires of n- and p-type makes it possible to calculate the power factor P.f.= α2σ(T) . It was found that the power factor has a maximum value for n-type layers and p-type wires in a temperature range of about 300 K.  Taking into account that heat conductivity χ in thin layers is essentially lower than that in the bulk Bi2Te3 samples[3], it is reasonable to expect a considerable increase in the thermoelectric efficiency (figure of merit) ZT=α2σ/χ*T.  The results allow us to recommend the use of wires and layers of Bi2Te3 as two branches in micro – electro-thermal systems for thermoelectric applications. 

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<dc:creator>Nikolaeva, A.A.</dc:creator>
<dc:creator>Konopko, L.A.</dc:creator>
<dc:creator>Rogacki, K.</dc:creator>
<dc:creator>Huber, T.E.</dc:creator>
<dc:creator>Gherghișan, I.</dc:creator>
<dc:creator>Botnari, O.V.</dc:creator>
<dc:date>2018</dc:date>
<dc:description xml:lang='en'><p>In this paper, we present a study of Shubnikov de Haas (SdH) oscillations at 4.2 and 2.1 K and temperature dependences of thermopower &alpha;(T) and resistivity &rho;(T) for layers and wires based on Bi2Te3 topological insulators (TIs) in a range of 4.2&ndash;300 K. &nbsp;Single-crystal Bi2Te3 layers of <em>n</em>- and <em>p</em>-type with a thickness of 10&ndash;30 &mu;m were prepared by the mechanical exfoliation of layers from a bulk single-crystal ingot of a similar composition using a scotch tape. The mechanical exfoliation mostly results in breaking the Te(1) - Te(1) van der Waals bond and the formation of few-quintuples layers. The X-ray diffraction studies revealed that the layers had a single-crystal structure; the cleavage plane of the layers was perpendicular to the <em>C</em>3 trigonal axis. Glass-insulated Bi2Te3 microwires were prepared by the Ulitovsky&ndash;Taylor method [1]; in general, the microwire core had a polycristalline structure consisting of large disoriented single-crystal blocks. &nbsp;High quantum mobilities &mu;g~2*104 cm2/V*s were determined from SdH oscillations in longitudinal (<em>H</em>&iuml;&iuml;<em>I</em>) and transverse (<em>H</em><em>ᅩ</em><em>I</em>) magnetic fields of up to 14 T at 4.2&ndash;2.1 K; the mobilities are substantially higher than those in bulk Bi2Te3 samples of the same composition. &nbsp;A phase shift in SdH oscillations in longitudinal (<em>H</em>&iuml;&iuml;<em>I</em>) and transverse (<em>H</em>ᅩ<em>I</em>) magnetic fields was found at H&rarr;ꝏ, which is characteristic of the Dirac state of TIs at the surface [2]. &nbsp;Analysis of the experimental data on the temperature dependences of resistivity &rho;(T) and thermopower &alpha;(T) in layers and wires of <em>n</em>- and <em>p</em>-type makes it possible to calculate the power factor P.f.= &alpha;2&sigma;(T) . It was found that the power factor has a maximum value for <em>n</em>-type layers and <em>p</em>-type wires in a temperature range of about 300 K. &nbsp;Taking into account that heat conductivity &chi; in thin layers is essentially lower than that in the bulk Bi2Te3 samples[3], it is reasonable to expect a considerable increase in the thermoelectric efficiency (figure of merit) ZT=&alpha;2&sigma;/&chi;*T. &nbsp;The results allow us to recommend the use of wires and layers of Bi2Te3 as two branches in micro &ndash; electro-thermal systems for thermoelectric applications.</p><p>&nbsp;</p></dc:description>
<dc:source>Materials Science and Condensed Matter Physics (Ediția 9) 212-212</dc:source>
<dc:title>Dirac states and thermoelectric properties, topological insulators bi2te3 wires and layers</dc:title>
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