X-ray powder diffraction from carbon nanotubes and nanoparticles

We report detailed x-ray powder-diffraction measurements on a sample consisting of {~}60% carbon nanotubes and {~}40% carbon nanoparticles. These measurements demonstrate the existence of short-range interlayer stacking correlations. Our calculations show that such correlations should not be observable in idealized models of nanotubes. The observation of short-range interlayer correlations can be explained if many of the nanotubes and nanoparticles have polygonal cross sections, largely consisting of flat regions having graphitic interlayer correlations. This polygonization is almost certainly driven by the van der Waals interactions responsible for the ABAB stacking in crystalline graphite.