One-dimensional nature in transport property of SWNT thin film electrochemical transistor

Recent success in isolating single-walled carbon nanotubes (SWNTs) of narrow chirality distribution enabled making pure metallic (m-) and semiconducting (s-) SWNT films. Such films are expected to reflect the nature of individual SWNTs, that is their one dimensional subband structure. Therefore, it is interesting to investigate electronic transport in m- and s-SWNT films by controlling their Fermi level ($E_{F})$. Chemical doping or FET is unsuitable for the purpose because of the lack of precise and reversible $E_{F}$ controllability, and the narrow controllable $E_{F}$ range, respectively. The problems are solved by our electric double layer transistor technique,$^{1}$ where the gate voltage ($V_{G})$ is applied through an electrolyte. The conductance and optical absorption spectra of the resistance of s- and m-SWNT films were measured at various $V_{G}$. The conductance of the s-SWNT film showed stepwise change against $V_{G}$. The absorbance spectra indicate the steps correspond to reaching of the $E_{F}$ to a vHs. Furthermore, even m-SWNT films showed steep increases of conductance, demonstrating that the conductance strongly depend on the subband filling. $^{1}$ H. Shimotani et al., Appl. Phys. Lett. 88, 073104 (2006).