In situ assessment of carbon nanotube diameter distribution with photoelectron spectroscopy

In situ UV-photoelectron spectroscopy (He I and He II) was performed on multiwalled carbon nanotubes (CNTs) with clearly differentiated diameter distributions. A significant dependence of valence- and conduction-band characteristics on the mean CNT diameter was observed, which was determined by high-resolution TEM and micro-Raman spectroscopy. The decrease of relative intensity of the $\ensuremath{\pi}$ states at $\ensuremath{-}3\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ in the He II experiments, indicative of increasing rehybridization between orbitals, was directly correlated with decreasing mean diameters. Furthermore, a progressive broadening of the unoccupied ${\ensuremath{\sigma}}^{*}$ band at $7.6\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ was found in the He I spectra.