ABSTRACT
One-dimensional and conical carbon structures were reported as early as 1960 [1,2], however, no evidence of hollowness was presented at that time. Th e carbon nanotubes were discovered much later in 1991 [3], consisting of single or multiple layers of cylindrical graphene sheets. Th e morphology of all the derived structures of nanotubes was primarily cylindrical in nature with internal diameters ranging from 1 to 25 nm [4].
