POLYGONIZATION AND ANOMALOUS GRAPHENE INTERLAYER SPACING OF MULTI-WALLED CARBON NANOFIBERS

摘要

The graphene interlayer spacing in pure graphite is known to have a minimum value of d_(min) =0.3354 nm, while defective graphites typically have larger interlayer spacings. Using transmission electron microscopy, we find that the nanofibers are polygonized after heat treatment above 2800K. And X-ray diffraction study reveals that the interlayer spacing of the treated carbon nanofibers is distinctly smaller than d_(min). To explain this unusual observation, we investigate the structural properties of carbon nanotubes using a multi-scale approach rooted in extensive first-principles calculations, specifically allowing the nanotube cross-sections to polygonize. We show that, it is energetically accessible at high temperatures to polygonize the nanotubes with large cross-sections (30-200 nm), accompanied by reductions in the graphene interlayer spacing. These unique predictions are confirmed in further experimental observations.