Probing the Thermoelectricity in Single Carbon Nanocoil for the Design of a Nano Thermocouple

Carbon nanocoils (CNCs) have been discovered and studied for years. Its good electrical conductivity and low lattice thermal conductivity suggest the application potential in thermoelectricity, which was studied for the first time in this work. Individual CNCs were suspended between two substrates with electrical heaters to create the desired temperature differences. Employing a transient electro-thermal technique, the thermoelectric, electrical, and heat transport properties of CNCs from 298 to 343 K before and after in situ Joule annealing were characterized simultaneously. CNCs exhibit asymmetric thermoelectric responses, with average Seebeck coefficients along the two length directions of 1.5 and 0.9 μV/K. This asymmetry results from different bandgaps along the growth direction, and the small Seebeck coefficient results from strong mixed electrical conductivity. The Fermi energy and optical bandgap of CNCs were measured to be 11.2 and 58.2 meV, respectively, with a small hole–electron conductivity ratio (1.36). The Seebeck coefficient shows a negative correlation with the electrical conductivity, while the thermal conductivity shows no observable correlation with them, hovering around 8.3 W/m K at room temperature. Doping may be an effective strategy to increase the Seebeck coefficient and electrical conductivity while decreasing the thermal conductivity for improved thermoelectric conversion. In addition, a flexible nanothermocouple based on two intertwined single CNCs was developed, which shows excellent response to thermal excitation.