Ab initio study of uniaxial strain-induced thermoelectric property tuning of individual single-wall carbon nanotubes

Carbon nanotubes (CNT) have garnered significant importance as thermoelectric (TE) material due to their high TE performance owing to their inherent fascinating one-dimensional quantum confinement of charge carriers. Among various methods to tune and enhance TE properties, the impact of strain on the properties of CNT-based TE devices is rarely explored, though it is immanently present, specifically on multi-functional CNT fibers. In this study, we present the tunability and enhancement of electronic and TE properties of single-wall carbon nanotubes (SWCNTs) by strain engineering within the framework of density functional theory and Boltzmann transport theory. Semiconducting to metallic transition with a zigzag pattern of band gap (Eg) and Seebeck coefficient (S) variation was observed for uniaxial strain due to shifting of the Dirac points. Within the smaller range of strains, the Eg and S for the (10,0) SWCNT exhibited a positive correlation with tensile strain and demonstrated a negative correlation with compressive strain, while it showed a reverse trend for (11,0) SWCNT. In contrast, for (9,0) SWCNT, the Eg and S increased under both tensile and compressive strains. The SWCNTs exhibited a significant enhancement of thermoelectric transport properties while they underwent tensile and compressive strains. Applying uniaxial stress enhanced the Seebeck coefficient of SWCNTs to 1580 μV K−1. We achieved the enhancement of thermoelectric power factor as follows: 2.2 mW m−1 K−2 (−9%), 1.3 mW m−1 K−2 (−3%), 1.15 mW m−1 K−2 (−3%), and 1.24 mW m−1 K−2 (−9%) for (6,6), (9,0), (10,0), and (11,0) SWCNTs, respectively. The overall performance parameter thermoelectric figure of merit, zT was tuned up to 1.56 when the strain varied from −9% to +9%, a fewfold increment compared to its relaxed state. The optimum range of doping for SWCNTs was found to be within 5 × 1019 cm−3– 1 × 1021 cm−3 to achieve the best thermoelectric power factor and zT. The insights gained from this study will be indispensable for diverse applications in the solid-state and especially in fiber-based wearable nanoelectronic devices such as strain sensors, thermoelectric energy harvesters, and thermoelectric coolers.