(A) study on phase stability of Pt nanoclusters on the graphite through molecular dynamics simulation

Abstract

A molecular dynamics (MD) simulation with an embedded atom scheme is used to investigate the phase stability of Pt nanoclusters and them on the graphite, $Pt_n$ (n = 38, 147, 309 and 561) atoms, under various temperature conditions. The heating and freezing behaviors show that the $Pt_{147}$, $Pt_{309}$ and $Pt_{561}$ clusters larger than 1 nm have icosahedra morphologies near 540~620 K during freezing, where their formation energies are 0.051 eV/atom for $Pt_{147}$, 0.056 eV/atom for $Pt_{309}$ and 0.067 eV/atom for $Pt_{561}$, respectively. On the other hand, when the two Pt nanoclusters interact with each other, they rapidly collide with each other and it is thermodynamically stable process. In addition, the free energy change estimated based on the Gibbs-Thomson effect for the coalescence phenomenon is found to be consistent with our MD simulation result. Moreover, we investigate the coalescence of Pt nanocluster on the graphite. In comparison with above result, we observed that the flat surface at the bottom of cluster and this disturbs forming the spherical shape. Therefore, we cannot find Icosahedron structure on the graphite layer. Moreover, the coalescent phenomenon was accelerated as the temperature rises and we find the completely coalescent phenomenon at 1000 K. However, experimental temperature of the synthesis of Pt nanocluster on the graphite layer is around 500 K. Therefore, we can find not only spherical Pt nanocluster but also peanut-like Pt nanocluster at the graphite layer.