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ACS Nano. 2019 Aug 27;13(8):9182-9189. doi: 10.1021/acsnano.9b03521. Epub 2019 Aug 16.

Enhanced Thermoelectric Performance of As-Grown Suspended Graphene Nanoribbons.

Author information

1
Department of Aeronautics and Astronautics , Kyushu University , Fukuoka 819-0395 , Japan.
2
International Institute for Carbon Neutral Energy Research (WPI-I2CNER) , Kyushu University , Fukuoka 819-0395 , Japan.
3
Materials Science and Technology Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States.
4
School of Mechanical Engineering and the Birck Nanotechnology Center , Purdue University , West Lafayette , Indiana 47907-2088 , United States.
5
Department of Electronic Engineering , Tohoku University , Aoba 6-6-05, Aramaki, Aoba-ku , Sendai 980-8579 , Japan.
6
Japan Science and Technology Agency (JST)-PRESTO , Aoba 6-6-05 , Aramaki, Aoba-ku, Sendai 980-8579 , Japan.

Abstract

Conventionally, graphene is a poor thermoelectric material with a low figure of merit (ZT) of 10-4-10-3. Although nanostructuring was proposed to improve the thermoelectric performance of graphene, little experimental progress has been accomplished. Here, we carefully fabricated as-grown suspended graphene nanoribbons with quarter-micron length and ∼40 nm width. The ratio of electrical to thermal conductivity was enhanced by 1-2 orders of magnitude, and the Seebeck coefficient was several times larger than bulk graphene, which yielded record-high ZT values up to ∼0.1. Moreover, we observed a record-high electronic contribution of ∼20% to the total thermal conductivity in the nanoribbon. Concurrent phonon Boltzmann transport simulations reveal that the reduction of lattice thermal conductivity is mainly attributed to quasi-ballistic phonon transport. The record-high ratio of electrical to thermal conductivity was enabled by the disparate electron and phonon mean free paths as well as the clean samples, and the enhanced Seebeck coefficient was attributed to the band gap opening. Our work not only demonstrates that electron and phonon transport can be fundamentally tuned and decoupled in graphene but also indicates that graphene with appropriate nanostructures can be very promising thermoelectric materials.

KEYWORDS:

Seebeck coefficient; electrical conductivity; phonon transport; suspended graphene nanoribbon; thermoelectricity

PMID:
31411858
DOI:
10.1021/acsnano.9b03521

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