Probing the Variation of Seebeck Coefficient of Carbon Nanotube Fibers Using Photothermoelectric Effect

Carbon Nanotube (CNT) fibers are promising candidates for thermoelectric materials because of their high value of power factor. However, the outstanding properties of CNT fibers are mostly discussed and investigated at the scale of the whole fiber and there's a lack of understanding of the local properties along the fibers. Here, we develop a method to study the variation of the Seebeck coefficient along the fibers using the photothermoelectric (PTE) effect. A laser spot which can move along the fiber is used as a localized heat source to generate the thermal voltage. The Seebeck coefficient as a function of position along the fiber can be calculated from the thermal voltage and modeled temperature profile. The Seebeck coefficient of fibers with different doping level is determined and agrees with the traditional average values. We also observe a correlation between the variation of the Seebeck coefficient and the shift of Raman modes, which is related to the doping level along the fiber. Our study provides a non-destructive method to quantify the uniformity of the CNT fibers at the micrometer scale and is helpful for fabricating more uniform and higher quality CNT fibers.