Origin of Capacitance Change in Semiconducting and Metallic Carbon Nanotubes

Different mechanisms are reported for the capacitance changes in metallic (m-) and semiconducting (s-) single-walled carbon nanotubes (SWCNTs) upon gas adsorption. The sensitivity, i.e., the change in capacitance, was high and reached approximately 2500{\%} in the aligned s-SWCNT network, whereas the sensitivity was found to be low in the m-SWCNT network. The charge transfer/Fermi level shift and quantum capacitance related to the localized electronic density of states near the Fermi level were key contributors to sensitivity changes upon gas adsorption, although the polarization effect also played a role in the capacitance changes, particularly in the aligned CNTs, under a strong electric field.