Interrelationships Among Carbon Nanostructures

Carbon nanostructures such as nanotubes, fullerenes, and diamond nanocrystals are receiving increasing attention because of their interest both from fundamental and applied points of view. Interrelationships between the properties of all groups of carbon entities at the nanoscale need to be better understood so that the energetics and conditions under which one form transforms to another can be rationalized. We present primarily electronic structure calculations showing in detail the growth mechanism of ultrananocrystalline diamond, which results from the reaction of the carbon dimer, C2, with the (110) diamond surface. The evolution of a new monolayer of the diamond lattice is traced from the initial reaction of a single C2 molecule, to the half-monolayer stage to the completed monolayer. Fullerene- and nanotubelike intermediate structural elements appear on the diamond surface during growth. The challenge will be to relate these calculations to studies mentioned below and to gauge the extent to which our current knowledge can lead to an integrated systematics of carbon nanostructures. Recent calculations by Barnard et al. delineate the stability relationships between diamond clusters, fullerenes and hydrogenated graphite clusters based on size ranges, while the transition of diamond nanocrystals to carbon onions was simulated by Fugaciu and Hermann. Again a comparison of the stability of fullerenes and closed nanotubes was made by Park et al. If the various known members of the nanocarbon family are related to each other by yet to be discovered hierarchical structures, it is possible that insight into the criteria determining the stability of each structure could lead to new, hitherto unknown family members with interesting and useful properties.