Invited Presentation: On the Viability of Helical Arrangement of Carbon Nanotube Via Supported Catalyst Structure: Graphene Embryo As a Precursor for Symmetry Formation

Wednesday, May 14, 2014: 14:20
Bonnet Creek Ballroom XII, Lobby Level (Hilton Orlando Bonnet Creek)
A. R. Harutyunyan (Honda Research Institute USA Inc)
Understanding of controlled growth of carbon nanotubes (CNTs) is critical for their broader applications and for catalysis in general. The problem remains elusive owing to complex interplay between nanotube nucleation and catalyst morphology reconstruction in the early stages during which the symmetry is set. Exploitation of in situ transmission electron microscopy for studies of carbon nanotube cap formation reveals that the nucleation begins by the creation of a graphene embryo bounded between opposite step edges on the catalyst surface. The embryo evolves into a cap when at least one of the steps flows and crosses the edges of adjacent facets on the catalyst tip. Further motion of the steps away from the catalyst tip with attached rims of carbon cap generates the tubular wall of the nanotube. Hence, CNT nucleation at low temperatures is a result of dynamic rearrangement of the graphene embryo edge-catalyst step interface structure. This implies that the symmetry formation concept driven by catalyst facet structure is very simplified, whereas the interrelationship between the structures of adjacent facets that introduces the curvature on graphene embryo plays the dominant role in the cap and thereby symmetry formation via self consistent manner. The roles of catalyst composition, size, structures of facets and corresponding step/terraces on the tube nucleation and symmetry formation will be presented in light of these new developments.