Lim Gyumin, Kihm Kenneth David, Kim Hong Goo, Lee Woorim, Lee Woomin, Pyun Kyung Rok, Cheon Sosan, Lee Phillip, Min Jin Young, Ko Seung Hwan
School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 08826, Korea.
Department of Mechanical, Aerospace, and Biomedical Engineering, University of Tennessee, Knoxville, TN 37996, USA.
Nanomaterials (Basel). 2018 Jul 22;8(7):557. doi: 10.3390/nano8070557.
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 , , and . Electrical conductivity () and Seebeck coefficients () 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 () 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 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 () 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.
通过改变前驱体气体流速、操作温度和腔室压力来控制化学气相沉积（CVD）石墨烯的晶粒尺寸。高质量且全覆盖地合成了平均晶粒尺寸分别为4.1 µm、2.2 µm和0.5 µm的石墨烯。通过研究晶粒尺寸对石墨烯的三种基本热学和电学性质（电导率（σ）、塞贝克系数（S）和迁移率（μ））的影响，展示了调整石墨烯热电转换特性的可能性。在真空中对SiO₂/Si场效应晶体管（FET）衬底上的负载型石墨烯测量电导率（σ）和塞贝克系数（S），以便通过施加栅极电压（VG）来改变电荷载流子密度。从测量的σ与VG关系图的斜率分别得到4.1 µm、2.2 µm和0.5 µm三种晶粒尺寸的空穴迁移率（μ）值为529、459和314 cm²/V·s，电子迁移率（μ）值为1042、745和490 cm²/V·s。随着晶粒尺寸减小，功率因子（PF）（热电品质因数（ZT）的电学部分）降低约一半，而对于相同的晶粒尺寸减小，热导率（κ）降低四分之一。最后，当晶粒尺寸从4.1 µm减小到0.5 µm时，所得的ZT增加了两倍多。
