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Open AccessArticle

Enhanced Thermoelectric Conversion Efficiency of CVD Graphene with Reduced Grain Sizes

1
School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 08826, Korea
2
Department of Mechanical, Aerospace, and Biomedical Engineering, University of Tennessee, Knoxville, TN 37996, USA
3
Korea Institute of Science and Technology, Seoul 02792, Korea
4
School of Mechanical Engineering, Korea University, Seoul 02841, Korea
5
Institute of Advanced Machinery and Design (SNU-IAMD), Seoul National University, Gwanak-ro, Gwanak-gu, Seoul 08826, Korea
*
Author to whom correspondence should be addressed.
Nanomaterials 2018, 8(7), 557; https://doi.org/10.3390/nano8070557
Received: 23 June 2018 / Revised: 8 July 2018 / Accepted: 16 July 2018 / Published: 22 July 2018
(This article belongs to the Special Issue Nanomaterials for Renewable and Sustainable Energy)
The grain size of CVD (Chemical Vapor Deposition) graphene was controlled by changing the precursor gas flow rates, operation temperature, and chamber pressure. Graphene of average grain sizes of 4.1 µm, 2.2 µm, and 0.5 µm was synthesized in high quality and full coverage. The possibility to tailor the thermoelectric conversion characteristics of graphene has been exhibited by examining the grain size effect on the three elementary thermal and electrical properties of σ, S, and k. Electrical conductivity (σ) and Seebeck coefficients (S) were measured in a vacuum for supported graphene on SiO2/Si FET (Field Effect Transistor) substrates so that the charge carrier density could be changed by applying a gate voltage (VG). Mobility (µ) values of 529, 459, and 314 cm2/V·s for holes and 1042, 745, and 490 cm2/V·s for electrons for the three grain sizes of 4.1 µm, 2.2 µm, and 0.5 µm, respectively, were obtained from the slopes of the measured σ vs. VG graphs. The power factor (PF), the electrical portion of the thermoelectric figure of merit (ZT), decreased by about one half as the grain size was decreased, while the thermal conductivity (k) decreased by one quarter for the same grain decrease. Finally, the resulting ZT increased more than two times when the grain size was reduced from 4.1 µm to 0.5 µm. View Full-Text
Keywords: thermoelectric conversion efficiency; CVD graphene; grain sizes; FET 4-point measurements; electrical conductivity; Seebeck coefficient thermoelectric conversion efficiency; CVD graphene; grain sizes; FET 4-point measurements; electrical conductivity; Seebeck coefficient
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MDPI and ACS Style

Lim, G.; Kihm, K.D.; Kim, H.G.; Lee, W.; Lee, W.; Pyun, K.R.; Cheon, S.; Lee, P.; Min, J.Y.; Ko, S.H. Enhanced Thermoelectric Conversion Efficiency of CVD Graphene with Reduced Grain Sizes. Nanomaterials 2018, 8, 557.

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