Dislocations in carbon nanotube walls.

We present a novel interpretation of defected tubes based on a dislocation model. A scroll (a sheet rolled without closure) is considered as an axial edge dislocation in a multiwall nanotube (MWNT). Screw dislocation type defects separate scroll from nested-tubes within the same nanotube. The glide of the screw dislocation causes the transformation between these two forms. In some cases, the mechanism of formation of an MWNT could, therefore, start with the formation of a scroll which, by gliding of a screw dislocation, is transformed into the more stable MWNT We compare the structure and energetics of prismatic screw and edge dislocations in graphite and carbon nanotubes. We present calculations for the Peierls barrier of the first kind for graphite and we discuss this result for glide motion of screw dislocations in nanotubes. There is no evidence for stable sp3 atoms in any of the studied nanostructures.