Fig. 2.

Appearance of the intersubband plasmon (ISBP) peak in a gated and aligned carbon nanotube film in polarized absorption spectra. a Optical and b scanning electron microscopy images of an aligned SWCNT film. The white horizontal bar in a represents a length of 100 nm. c Schematic diagram for the setup for the polarization-dependent absorption spectroscopy experiments on an aligned SWCNT film gated through electrolyte gating. V_G: gate voltage, R: reference voltage. d Parallel-polarization and e perpendicular-polarization optical absorption spectra at different gate voltages for an aligned SWCNT film containing semiconducting and metallic nanotubes with an average diameter of 1.4 nm. The ISBP peak appears only for perpendicular polarization (e) for both electron and hole doping, corresponding to V_G = −2.0 and 4.3 V, respectively