Impedance and Capacitance Measurement of Individual Carbon Nanotubes

Abstract

We experimentally examined the impedance of individual single wall carbon nanotubes (SWNT) in the frequency range of 40 Hz to 110 MHz. The tubes were assembled as a conducting channel of field‐effect transistor (FET) structures from aqueous suspension using dielectrophoresis. At the low frequency limit the impedance is independent of the frequency and equivalent to real resistance. We observe a sharp conductor‐insulator transition at a crossover frequency of about 2.5 MHz, above which the circuit response becomes capacitive. The extracted SWNT capacitance, CSWNT, of about 4 10−14 F/μm, is independent of the total real resistance, however the CSWNT value is larger than that theoretically predicted quantum capacitance CQE. Within this formalism we estimate that the effective Fermi velocity of charge carriers, vF, for our SWNT is about 103 m/s, which is about two orders of magnitude below vF of a perfect tube. Our results agree qualitatively with the theoretical impedance characteristic of a SWNT, and furthe...