Photoemission Study of One-Dimensional Electronic States of (6,5), (6,6), and (7,4) Single-Walled Carbon Nanotubes

We have investigated the one-dimensional electronic states of single-walled carbon nanotubes (SWCNTs) with diameters ranging from 0.8-1.4 nm by optical absorption, photoemission, and inverse photoemission measurements. In the photoemission spectra of (6,5) SWCNTs and (6,6)- and (7,4)-enriched SWCNTs, spike structures caused by Van Hove singularities (VHSs) are clearly observed. The observed VHS positions are compared with the positions calculated using the tight-binding model and density functional theory. A large curvature affects the electronic states of metallic SWCNTs with small diameters.