Nanoscale View Article Online FEATURE ARTICLE View Journal | View Issue Atomistic modelling of CVD synthesis of carbon nanotubes and graphene Cite this: Nanoscale, 2013, 5, 6662 James A. Elliott,*a Yasushi Shibuta,b Hakim Amara,c Christophe Bicharad and Erik C. Neytse We discuss the synthesis of carbon nanotubes (CNTs) and graphene by catalytic chemical vapour deposition (CCVD) and plasma-enhanced CVD (PECVD), summarising the state-of-the-art understanding of mechanisms controlling their growth rate, chiral angle, number of layers (walls), diameter, length and quality (defects), before presenting a new model for 2D nucleation of a graphene sheet from amorphous carbon on a nickel surface. Although many groups have modelled this process using a variety of techniques, we ask whether there are any complementary ideas emerging from the different proposed growth mechanisms, and whether different modelling techniques can give the same answers for a given mechanism. Subsequently, by comparing the results of tight-binding, semi-empirical fi Creative Commons Attribution 3.0 Unported Licence. molecular orbital theory and reactive bond order force eld calculations, we demonstrate that graphene on crystalline Ni(111) is thermodynamically stable with respect to the corresponding amorphous metal and carbon structures. Finally, we show in principle how a complementary heterogeneous nucleation Received 17th April 2013 step may play a key role in the transformation from amorphous carbon to graphene on the metal Accepted 5th June 2013 surface. We conclude that achieving the conditions under which this complementary crystallisation DOI: 10.1039/c3nr01925j process can occur may be a promising method to gain better control over the growth processes of both www.rsc.org/nanoscale graphene from flat metal surfaces and CNTs from catalyst nanoparticles. This article is licensed under a aDepartment of Materials Science and Metallurgy, University of Cambridge, dAix-Marseille Universit´e, CNRS, CINaM UMR 7325, 13288 Marseille, France. Pembroke Street, Cambridge, CB2 3QZ, UK. E-mail: [email protected] E-mail: [email protected] bDepartment of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, eDepartment of Chemistry, PLASMANT Research Group, University of Antwerp, Open Access Article. Published on 06 June 2013. Downloaded 9/25/2021 6:19:20 PM. Bunkyo-ku, Tokyo 113-8656, Japan. E-mail: [email protected] Universiteitsplein 1, B-2610 Wilrijk-Antwerp, Belgium. E-mail: [email protected] cLaboratoire d'Etudes des Microstructures, ONERA-CNRS, BP 72, 92322 Chatillonˆ Cedex, France. E-mail: [email protected] James Elliott is a Reader in Yasushi Shibuta has been a Macromolecular Materials in Lecturer at the University of the University of Cambridge, Tokyo (UT) since 2011. He where he carries out research on received his PhD from UT in multiscale computational 2004. Aer being a JSPS Post- modelling of so matter doctoral Research Fellow, he systems, including coarse- joined the Department of Mate- grained and molecular model- rials Engineering, UT as an ling of polymers, carbon nano- Assistant Professor at 2005. He tubes and their composites. He was a Visiting Fellow at Fitz- obtained his MA in Natural william College, Cambridge, UK Sciences (Physics) from Cam- in 2005 and 2006. His recent bridge, and his PhD in Polymer research focuses on under- Physics at the University of Bristol. He was a JSPS Invitation Fellow standing the nature of phase transitions during the synthesis of and Visiting Professor at the University of Tokyo in 2008, and materials by numerical modelling. His chosen systems of interest collaborates with several groups working on CNT synthesis and range from base materials such as iron and steel to advanced thermal properties of CNT-polymer composites. http:// materials such as carbon nanotubes and graphene. http:// www.elliotts.org.uk www.mse.t.u-tokyo.ac.jp/shibuta/ 6662 | Nanoscale, 2013, 5, 6662–6676 This journal is ª The Royal Society of Chemistry 2013 View Article Online Feature Article Nanoscale Introduction experimental CVD synthesis methods and proposed mecha- nisms for nucleation and growth, before summarizing previous The rst single-wall carbon nanotubes (SWCNTs) were syn- computational work. We then conclude with a comparative thesised by high temperature techniques (e.g. laser ablation and analysis of our own recent simulation results of carbon on arc discharge1), all of which involve a metal catalyst. In these nickel, based on which we propose a complementary hetero- methods, carbon and transition metal (TM) elements (such as geneous nucleation step for the transformation of amorphous Co, Ni, Fe, etc.) are vapourised at temperatures above 3000 K carbon to graphene on the metal surface. and then condensed at lower temperatures in an inert gas (He or Ar) ow. SWCNTs and multi-wall carbon nanotubes Experimental CVD synthesis methods (MWCNTs) are now commonly produced by catalytic chemical vapour deposition (CCVD) at much lower temperatures, ranging For 50 years, the formation of lamentous carbon by catalytic from 600–1300 K, or by plasma-enhanced CVD (PECVD), in decomposition of gases has been intensively studied, mainly due 2 ff which the gas is not activated by high temperatures as in to its role in industrial chemical processes. Much e ort has thermal CCVD, but rather by applying a sufficiently strong since been devoted to adapting CCVD methods to the synthesis voltage, causing gas breakdown. There is currently great interest of SWCNTs, MWCNTs, and lately graphene. In the case of CNTs, in adapting these techniques for production of high-quality it is known that the nanotube grows from a TM nanoparticle that single- and few-layer graphene. Here, we restrict our attention to is either attached to a substrate, o en silica or alumina, or CNTs and graphene produced by CVD methods, which are oating in a gas phase reactor. Depending on the growth ff widely used due to their low cost and ease of scaling to indus- temperature, di erent products are obtained. Although there is trial production. We begin by briey reviewing existing no absolute rule, the general tendency is to obtain MWCNTs at medium temperatures (between 600 and 1000 K) and SWCNTs at higher temperatures (between 900 and 1300 K) although there are some exceptions to this discussed below. The process is Creative Commons Attribution 3.0 Unported Licence. Hakim Amara is a senior scientist complex, but it is accepted that the metal nanoparticle acts as a working at ONERA (French Aero- catalyst to favour the decomposition of the carbon-bearing space Lab) who has received his precursor (typically C2H2,C2H4,CH4 or alcohols). The nano- PhD in Material Science in 2005. particle also serves as a heterogeneous surface on which the His main interest lies in theoret- initial nanotube cap can grow, leading to the formation of long ical condensed matter physics. tubes. In the case of graphene, for metals with low carbon solu- He has an expertise in the devel- bility such as Cu, nucleation is initiated at impurities or defects opment of numerical computa- on the metal surface, and growth proceeds from the edges of the This article is licensed under a tions at the atomic scale using nascent sheet, typically leading to single- or few-layer graphene. tight-binding and ab initio tech- For metals with higher carbon solubility, such as Ni, the domi- niques. Current research focuses nant mechanism is surface segregation and precipitation of Open Access Article. Published on 06 June 2013. Downloaded 9/25/2021 6:19:20 PM. on modelling of nucleation and dissolved carbon, typically leading to multi-layer graphene. growth mechanisms of carbon Although the products obtained from the medium temper- nanotubes and graphene from metallic catalysts and also electronic ature methods have a lower quality (as measured by their crys- properties (STM images) of defects in carbon nanostructures. talline order) than those produced by the high temperature Christophe Bichara is Research Erik Neyts is appointed as tenure Director at CNRS with an track professor at the University expertise in Condensed Matter of Antwerp (UA). Aer his PhD in Physics, Chemical Physics and chemistry on molecular Computational Materials dynamics (MD) simulations for Science. He graduated in the deposition of diamond-like Chemical Engineering (Toulouse carbon layers, he investigated – 1979) and obtained a “Doc- the deposition of metal oxide torat `es Science” (Marseille – layers by MD and Monte Carlo 1987). His current interest lies (MC) simulations as a post- in the study of disorder, liquid doctoral researcher. His current matter, non-crystalline mate- work focuses on MD/MC simu- rials as well as the growth lations for the growth of nano- mechanisms of carbon structured materials, including carbon nanotubes, graphene and nanostructures. silicon oxide nanowires. Recently, new research directions were launched focusing on the study of plasma catalysis and plasma medicine by MD/MC simulations as well. This journal is ª The Royal Society of Chemistry 2013 Nanoscale, 2013, 5, 6662–6676 | 6663 View Article Online Nanoscale Feature Article routes, the CCVD method has numerous advantages especially applying a sufficiently strong voltage, causing gas breakdown. in terms of control of the growth conditions. In the case of Indeed, this leads to the creation of a plethora of reactive CNTs, growth can be precisely localised using a lithographically species, including electrons and ions, neutral molecules, patterned catalyst.3 In this respect, vertically-oriented SWCNT molecular radicals and atoms, and photons, in addition to the carpets or forests grown by CCVD have received enormous presence of electromagnetic elds. All of these factors attention because of their suitability in a number of important contribute to a number of advantages of PECVD growth over technological applications.4,5 To promote growth and avoid any thermal growth.25 For example, since the gas activation in poisoning effect that prevents it, water has been used as a PECVD does not require a high temperature, there is no high protective agent against coating by amorphous carbon.