Isotropic Seebeck coefficient of aligned single-wall carbon nanotube films

• Published in: Applied physics letters Vol. 113; no. 24
• Main Authors: Fukuhara, Kengo, Ichinose, Yota, Nishidome, Hiroyuki, Yomogida, Yohei, Katsutani, Fumiya, Komatsu, Natsumi, Gao, Weilu, Kono, Junichiro, Yanagi, Kazuhiro
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 10.12.2018; American Institute of Physics (AIP)
• Subjects: Alignment; Anisotropy; Applied physics; Assembly; Carbon; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Density of states; Electrical conductivity; Electrical resistivity; Electrolytes; Fermi level; Hopping conduction; Hopping transport; Morphology; Nanomaterials; Nanotubes; Physics; Seebeck effect; Single wall carbon nanotubes; Thermoelectric effects; Thermoelectric materials; Thermoelectricity; Thin films
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.5066021

How the morphology of a macroscopic assembly of nanoobjects affects its properties is a long-standing question in nanomaterials science and engineering. Here, we examine how the thermoelectric properties of a flexible thin film of carbon nanotubes depend on macroscopic nanotube alignment. Specifically, we have investigated the anisotropy of the Seebeck coefficient of aligned and gated single-wall carbon nanotube thin films. We varied the Fermi level in a wide range, covering both the p-type and n-type regimes, using electrolyte gating. While we found the electrical conductivity along the nanotube alignment direction to be several times larger than that in the perpendicular direction, the Seebeck coefficient was found to be fully isotropic, irrespective of the Fermi level position. We provide an explanation for this striking difference in anisotropy between the conductivity and the Seebeck coefficient using Mott's theory of hopping conduction. Our experimental evidence for an isotropic Seebeck coefficient in an anisotropic nanotube assembly suggests a route toward controlling the thermoelectric performance of carbon nanotube thin films through morphology control.