Assembling Structure of Single-Walled Carbon Nanotube Thin Bundles

Atomic force microscopy (AFM), high resolution transmission electron microscopy, and Raman spectroscopy were used to study the assembling structure of thin bundles containing only a few single-walled carbon nanotubes (SWCNTs). The normal close-packed bundles as well as two novel kinds of bundles including spiral bundles and the ribbon-like bundles were observed for both free-standing SWCNTs and SWCNTs on substrates. Molecular mechanics calculation was employed to study the energetic competition between these three types of bundles. It was found that the free-standing spiral bundles and ribbon-like bundles are metastable compared with the close-packed bundles. However, ribbon-like bundles are more likely to be formed on substrates. This indicates that it is not reliable to assess whether the tested nanotube is individual through the height profile of the AFM image.