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Catalyst faceting during graphene layer crystallization in the course of carbon nanofiber growth
Maurice, J.L.,Pribat, D.,He, Z.,Patriarche, G.,Cojocaru, C.S. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.79 No.-
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 catalyst particles. 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 the mechanisms 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.
Etchant-induced shaping of nanoparticle catalysts during chemical vapour growth of carbon nanofibres
He, Z.B.,Maurice, J.L.,Lee, C.S.,Gohier, A.,Pribat, D.,Legagneux, P.,Cojocaru, C.S. Pergamon Press ; Elsevier Science Ltd 2011 Carbon Vol.49 No.2
Carbon nanofibres (CNFs) obtained by plasma-enhanced chemical vapour deposition are made of cone-shaped graphene layers, the opening angle of which has a significant influence on their properties: the smaller the angle, the closer the properties to those of carbon nanotubes. That angle is determined by the shape of the metal nanoparticle used to catalyse the growth. We show in this paper that the shape of Ni nanoparticle catalysts, and in turn the CNF properties, can be tuned during plasma-enhanced chemical vapour deposition, by the choice of the etchant gas. We show in particular that a water-containing etchant (H<SUB>2</SUB>O or H<SUB>2</SUB>O+H<SUB>2</SUB>) increases the growth rate by an order of magnitude at 600<SUP>o</SUP>C compared to an ammonia-containing etchant (NH<SUB>3</SUB> or NH<SUB>3</SUB>+H<SUB>2</SUB>), and leaves more elongated Ni particles with a cone angle three times smaller. We conclude that the cone angle and the growth rate are directly related, and propose a mechanism to explain that large difference between the two etchants
Electron emission from arrays of carbon nanotubes/fibres
W. I. Milne,K. B. K. Teo,M. Chhowalla,G. A. J. Amaratunga,D. Pribat,P. Legagneux,G. Pirio,Vu Thien Binh,V. Semet 한국물리학회 2002 Current Applied Physics Vol.2 No.6
The overall aim of this work is to produce arrays of eld emitting microguns, based on carbon nanotubes, which can be utilised inthe manufacture of large area eld emitting displays, parallel e-beam lithography systems and electron sources for high frequency(MWCNTs) using a dc plasma technique and a Ni catalyst. We will discuss how the density of the carbon nanotube/bres can bevaried by reducing the deposition yield through nickel interaction with a diusion layer or by direct lithographic patterning of the Nicatalyst to precisely dene the position of each nanotube/bre. Details of the eld emission behaviour of the dierent arrays ofMWCNTS will also be presented.. 2002 Published by Elsevier Science B.V.