Spectroscopic characterization of single-walled carbon nanotubes carrier-doped by encapsulation of TCNQ

Tetracyano-p-quinodimethane (TCNQ) molecules encapsulated single-walled carbon nanotubes (SWNTs) were investigated by using core level and valence band x-ray photoemission spectroscopy as well as near-edge x-ray-absorption fine structure spectroscopy. The $\pi$-band and ${\pi }^{*}$-band structures in these molecular systems were investigated, and it was clearly confirmed that a charge transfer occurred in TCNQ-doped SWNTs. TCNQ molecules were negatively charged as to be expected. A depletion of the $\pi$-band density of states of the SWNTs caused by the charge transfer to the TCNQ molecules was observed.