(318d) Formation of Carbon Structures On Stepped and Chiral Surfaces

Single-wall carbon nanotubes grow over catalytic nanoparticles via chemical vapor deposition methods, where a C-containing precursor gas is decomposed over the catalytic surface at ~ 1000 K. A few synthesis methods are able to produce nanotubes in a relative narrow range of chiralities; however the mechanism for such selectivity is not well understood. Our hypothesis is that the surface pattern is able to induce chirality of the nascent tube, and viceversa, under certain conditions carbon adsorption may yield surface reconstruction thus generating chiral surfaces. We present a density functional theory study of adsorption of single carbon atoms and carbon chains on stepped transition metal surfaces, using the projector-augmented wave method and the Perdew-Burke-Ernzerhof exchange-correlation functional, within the generalized gradient approximation. We discuss a series of interesting carbon structures formed over the (211) Co surface which evolve as the C concentration on the surface increases. At low concentration of C we observe the formation of zig-zag chains where each of the atoms in the zigzag are alternatively bonded to a step and to a terrace site. After more carbon is added to the system, perfect graphene structures are formed.1 Interestingly, our findings are in excellent agreement to recently published experimental results.2,3 We use ab initio molecular dynamics to investigate the effect of temperature on the stability of the crabon structures, and we extend the study using chiral surfaces, to analyze if carbon atmospheres on chiral Co surfaces may also lead to the formation of alternative structures. Preliminary calculations suggest that horizontally aligned nanotubes could be also the result of surface patterning.

References

(1) Ramirez-Caballero, G. E.; Burgos, J. C.; Balbuena, P. B. Growth of carbon structures on stepped (211) cobalt surfaces J. Phys. Chem. C 2009, in press.

(2) Zhu, H.; Suenaga, K.; Hashimoto, A.; Urita, K.; Hata, K.; Iijima, S. Atomic-resolution imaging of the nucleation points of single-wall carbon nanotubes Small 2005, 1, 1180.

(3) Zhu, H.; Suenaga, K.; Wei, J.; Wang, K.; Wu, D. A strategy to control the chirality of single-wall carbon nanotubes J. of Crystal Growth 2008, 310, 5473.