Nanoparticle Growth Analysis by Molecular Dynamics: Cubic Seed

Growth of a cubic nanoparticle was studied by classical molecular dynamics simulation for three seed sizes in nine different supersaturation ratios. Similar to the spherical seed in our previous study, for high supersaturation ratios, a two-stage phenomenon that consists of an initial heterogeneous growth around the seed and homogeneous nucleation at various sites within the system was observed. A decomposition of the distinct phenomenon was carried out and the results were compared to that from the spherical seed. The homogeneous nucleation characteristics for high supersaturation ratios show no significant difference, but as the supersaturation ratio decreases, the ratio of the nucleation rate for the systems with different seed shapes shows a deviation from unity. Other tendencies are nearly identical to that seen from the spherical seed study and the physical rationales are alike. The heterogeneous growth rate was greater by a factor of 3 to 10, even though the number of molecules in each seed class was nearly identical, which is evidence of a shape effect. Furthermore, cluster formation free energy analysis was conducted and the results were compared with the classical nucleation theory and condensation theory. The disk-shape modification of the classical nucleation theory was used for growth on the cubic seed and produced a similar deviation to that of the spherical seed, which used a cap-shape modification. Additionally, the condensation theory showed a better agreement compared with the sphere. Finally, the nanoparticle growth mechanism on the seeds along with the packing and surface diffusion characteristics was analyzed and showed why and how the nanoparticle grows.