Abstract Submitted to the    NANOTUBE'04 Conference:

Recent advances in in situ techniques for research in heterogeneous catalysis have opened up the possibility of studying gas-solid interactions at the atomic level (1). Here we present in situ transmission electron microscopy observations of carbon nanofibers growing by catalytic decomposition of methane over oxide-supported nickel nanocrystals (2). By means of time-resolved, high-resolution imaging, the carbon nanofibers are seen to develop through a reaction-induced reshaping of the nickel nanocrystals which assists the alignment of graphene layers into graphitic nanofibers. Specifically, the nucleation and the growth of graphene layers are found to couple to a dynamic formation and restructuring of mono-atomic step edges at the nickel surface. The finding that metallic step sites act as growth centers is attributed to the stronger bonding of carbon atoms to step sites than to facet sites (3). From an interplay with density functional theory calculations, the dynamic observations are consistently explained by a growth mechanism involving surface diffusion of nickel and carbon atoms.

(1) H. Topsoe, J. Catal. 216, 155 (2003).
(2) S. Helveg, C. López-Cartes, J. Sehested P. L. Hansen, B. S. Clausen, J. R. Rostrup-Nielsen, F. Abild-Pedersen, J. K. Nørskov, Nature 427, 426 (2004).
(3) H. S. Bengaard, J. K. Nørskov, B. S. Clausen, L. P. Nielsen, A. M. Molenbroek, J. R. Rostrup-Nielsen, J. Catal. 209, 365 (2002).