Self-organization of carbide superlattice and nucleation of carbon nanotubes.

Abstract

In metal-carbon systems with known stable compounds, carbide nanocrystals self-organize epitaxially on metal surfaces to form two-dimensional arrays during carbon deposition. The process is energetically driven by the competition between the strain and surface energies, and it appears to play an important role in the nucleation of single-walled carbon nanotubes. Interplay between energetics and kinetics controls carbon precipitation from the superlattice, such that the length scale of the carbide and superlattice appears to control the size and morphology of the precipitates. Furthermore, carbon precipitates appear to be "seedlings" of carbon nanotubes grown on top of the carbide nanocrystals. These findings reveal that the nucleation of carbon nanotubes is a nonequilibrium process and that a stable carbide superlattice can be used as an ordered template of carbon saturated "roots" for nucleating nanotube bundles with controlled diameter, spacing, and perhaps chirality.