Revealing the small-bundle internal structure of vertically aligned single-walled carbon nanotube films

Freestanding arrays of vertically aligned single-walled carbon nanotubes (VA-SWNTs) synthesized from alcohol were observed directly by transmission electron microscopy (TEM). These observations revealed that the films are comprised primarily of small bundles, containing 10 or fewer SWNTs per bundle. The absence of large, well-formed bundles is supported by electron diffraction spectra in which no bundle peak is observed. Furthermore, electron energy-loss spectroscopy shows an unusually low π plasmon energy, meaning dielectric screening from tube-tube interactions is insignificant. Not only does this suggest a prevalence of small bundles but it also indicates that the optical properties of the VA-SWNT array are determined by the one-dimensional nature of the component SWNTs, rather than the bulk dimensions of the entire SWNT film.