04 mai 2011

Based on numerical simulations, we have reached a new step in our understanding of the mechanisms that drive the growth of carbon nanotubes.


One of the most commonly used methods for synthesizing carbon nanotubes is chemical vapor deposition (CVD). The reaction involves a liquid catalyst placed on a substrate. This catalyst consists of metallic clusters (iron, cobalt, nickel…) whose size and shape, among other parameters, determine the properties of the nanotubes such as their diameter and quality. Since the details of the processes involved in the growth of nanotubes are not well understood at present, it is helpful to model the cluster properties by computer simulation.


The interactions between the few tens of atoms forming the cluster, as well as their interaction with the substrate and the carbon atoms, are the input parameters for the calculation. Using the molecular dynamics method, and by modeling the interaction between atoms of the cluster with a classical potential with parameters valid for bulk materials, we had in 2009 determined the shape of the clusters and their melting temperature as a function of the strength of the interaction with the substrate, as shown in the figure obtained for a cluster of Co55.


However, for clusters with so few atoms, quantum effects that were not accounted for in the above-mentioned work are important. We have recently modeled the interactions between the atoms by an ab initio quantum calculation, starting with sodium clusters as the first simple application. We find notable differences with the classical model regarding the shape and melting points of the clusters. We are now going to consider the metals which are used to grow nanotubes.


Further reading: Blundell SA et al., Physical Review B 84 (2011) 075430


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