The mechanism of transforming diamond nanowires to carbon nanostructures

摘要

The transformation of diamond nanowires (DNWs) with different diameters and geometries upon heating is investigated with density-functional-based tight-binding molecular dynamics. DNWs of h100i and h111i oriented cross-section with projected average line density between 7 and 20 atoms ?~(-1) transform into carbon nanotubes (CNTs) under gradual heating up to 3500-4000 K. DNWs with projected average line density larger than 25 atoms ?~(-1) transform into double-wall CNTs. The route of transformation into CNTs clearly exhibits three stages, with the intriguing intermediate structural motif of a carbon nanoscroll (CNS). Moreover, the morphology plays an important role in the transformation involving the CNS as one important intermediate motif to form CNTs. When starting with hN211i oriented DNWs with a square cross-section consisting of two f111g facets facing each other, one interesting structure with 'nano-bookshelf' shape emerges: a number of graphene 'shelves' located inside the CNT, bonding to the CNT walls with sp3 hybridized atoms. The nano-bookshelf structures exist in a wide range of temperatures up to 3000 K. The further transformation from nano-bookshelf structures depends on the strength of the joints connecting shelves with CNT walls. Notably, the nano-bookshelf structure can evolve into two end products: one is CNT via the CNS pathway, the other is graphene transformed directly from the nano-bookshelf structure at high temperature. This work sheds light on the microscopic insight of carbon nanostructure formation mechanisms with the featured motifs highlighted in the pathways.