Bonding and Stability of Hybrid Diamond/Nanotube Structures

Several recent experiments have provided compelling evidence for stable hybrid carbon nanotubediamond structures. In experiments by Kuznetsov et al. [1,2] the formation of nanometric closed curved graphitic structures with tubular or conical forms attached to a surface of a diamond particle were observed in high-resolution transmission electron microscopy (TEM) images of diamond particles after high-temperature annealing. The TEM images show concentric graphitic shells corresponding to the top view of nested carbon nanotubes as well as a side view of nanotubes on the edges of particles. The authors suggest that multi-layered graphitic caps that form during the initial annealing of micronsized diamond particles at 1800–2000 K transform into closed carbon nanotubes attached to the diamond surface via reconstruction of the edges of diamond (111) planes orthogonal to the surface into graphite (0001) planes. Avigal et al. [3] and Ayres et al. [4] have also recently reported simultaneous growth of hybrid structures of diamond crystallite and carbon nanotubes on the same substrate by plasma-enhanced chemical vapor deposition. There is an interesting and widely recognized geometrical similarity between the {111} planes of diamond and individual graphene sheets in which pairs of diamond planes resemble “puckered” graphite. This geometrical relationship together with the lengthening of carbon–carbon bonds from 1.42 Å in graphite to 1.54 Å in diamond results in the near epitaxial relations [14]