Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth

J.-L. Maurice (1) , Didier Pribat (2) , Z He (3) , G Patriarche (4) , Costel Sorin Cojocaru (1)

1 LPICM - Laboratoire de physique des interfaces et des couches minces [Palaiseau]
2 Department of Energy Science
3 State Key Laboratory for Advanced Metals and Materials
4 LPN - Laboratoire de photonique et de nanostructures

The low temperature catalytic growth of multiwall carbon nanotubes (MWCNTs) rests on the continuous nucleation and growth of graphene layers at the surface of crystalline catalystparticles. Here, we study the atomic mechanisms at work in this phenomenon, by observing the growth of such layers in situ in the transmission electron microscope, in the case of iron-based catalysts. Graphene layers, parallel to the catalyst surface, appear by a mechanism of step flow, where the atomic layers of catalyst are "replaced" by graphene planes. Quite remarkably, catalyst facets systematically develop while this mechanism is at work. We discuss the origin of faceting in terms of equilibrium particle shape and graphene layer nucleation. Step bunching due to impeded step migration, in certain growth conditions, yields characteristic catalyst nail-head shapes. Mastering themechanisms of faceting and step bunching could open up the way to tailoring the structure of low temperature-grown MWCNTs, e.g. with highly parallel carbon walls and, ultimately, with controlled structure and chirality.

Domaines: Science des matériaux [cond-mat.mtrl-sci]

J.-L. Maurice, Didier Pribat, Z He, G Patriarche, Costel Sorin Cojocaru. Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth. Carbon, 2014, 79, pp.93. ⟨10.1016/j.carbon.2014.07.047⟩. ⟨hal-01084443⟩