Postdoctorat CINaM : Marseille, France (2013-2015)

Phase diagram of Ni-C nanoparticles from computer simulation.

Carbon nanotube synthesis critically depends on the chemical and physical states of the catalyst particle from which they grow. In the typical temperature range (900-1300 K) of SWNT synthesis, pure isolated Ni nanoparticles are solid although atomic diffusion can lead to significant shape changes. Under growth conditions, these nanoparticles are exposed to reactive carbon. Depending on temperature, carbon chemical potential and nanoparticle size, carbon can either stay adsorbed on the surface, or diffuse to subsurface or in the core of the nanoparticle, thereby inducing a partial or complete melting. On the basis of the tight binding model developed for the Ni-C system coupled with grand canonical Monte Carlo simulations [1], we try and calculate size dependent solid/core-shell/liquid phase diagrams for Ni-C alloys. We thus extend our previous calculations [2, 3] and rationalize our findings using suitable order parameters, as proposed by Steinhardt et al. [4].

 Diag Phase NP

Figure 1 : Phase diagram of a Ni Wulff nanoparticle, 807 atoms.

[1] H. Amara et al., Phys. Rev. 79, 014109 (2009)
[2] M. Diarra et al.,Phys. Stat. Sol. B 249, 12, 2629 (2012)
[3] M. Diarra et al., Phys. Rev. Lett. 109, 185501 (2012)
[4] P. Steinhardt et al., Phys. Rev. B, 28, 784 (1983)