Diameter dependence of thermoelectric power of semiconducting carbon nanotubes

TL;DR

This study calculates the thermoelectric power of semiconducting carbon nanotubes, revealing that smaller diameters lead to significantly higher thermopower, with potential implications for thermoelectric applications.

Contribution

It provides a diameter-dependent analytical model for thermopower in semiconducting carbon nanotubes, linking thermopower directly to band gap and tube diameter.

Findings

Thermopower increases as nanotube diameter decreases.

Small-diameter nanotubes can have thermopower over 2000 μV/K.

Thermopower is directly related to the band gap of nanotubes.

Abstract

We calculate the thermoelectric power (or thermopower) of many semiconducting single wall carbon nanotubes (s-SWNTs) within a diameter range 0.5-1.5 nm by using the Boltzmann transport formalism combined with an extended tight-binding model. We find that the thermopower of s-SWNTs increases as the tube diameter decreases. For some s-SWNTs with diameters less than 0.6 nm, the thermopower can reach a value larger than 2000 {\mu}V/K at room temperature, which is about 6 to 10 times larger than that found in commonly used thermoelectric materials. The large thermopower values may be attributed to the one-dimensionality of the nanotubes and to the presence of large band gaps of the small-diameter s-SWNTs. We derive an analytical formula to reproduce the numerical calculation of the thermopower and we find that the thermopower of a given s-SWNT is directly related with its band gap. The formula also explains the shape of the thermopower as a function of tube diameter, which looks similar to the shape of the so-called Kataura plot of the band gap dependence on tube diameter.