Effect of bundling on the π plasmon energy in sub-nanometer single wall carbon nanotubes

Due to their unusual electronic and vibrational properties, single walled carbon nanotubes (SWCNTs) with sub-nanometer diameters d ∼ 0.5–0.9 nm have recently gained interest in the carbon community. Using UV–Vis–NIR spectroscopy and ultra-centrifugation, we have conducted a detailed study of the π plasmon energy (present at∼5–7 eV) in sub-nm SWCNTs as a function of the size of the bundle. We find that the energy of the π plasmon peak E varies with the bundle diameter Dh as E = (-0.023 eV)∗ln(Dh/do) + 5.37 eV, where do = 0.5 nm and corresponds to the smallest tube diameter.1 This is compared with the same data for HiPCo and Carbolex SWCNTs of larger diameter (1–1.4 nm) confirming a clear dependence of E on the bundle size, which is present in addition to the previously reported dependence of E on SWCNT diameter d.