Atomic-scale structure of Co-Pt bimetallic nanoparticles: Monte Carlo simulations

Co-Pt bimetallic nanoparticles (NPs) with icosahedral, decahedral, and truncated octahedral morphologies are obtained by using effective semigrand canonical ensemble Monte Carlo simulation, which is based on the second-moment approximation of the tight-binding potential. The simulation results show that Co atoms occupy first the central site, then diagonal lines or adjacent vertices positions, finally the vertices and edges as the Co mole fraction increases. We also study the binding-energy difference to investigate the relative structural stability of Co-Pt bimetallic nanoparticles. Atomic-scale structural properties are investigated by structure function and atomic pair-distribution function technologies. In the nanoparticles with about 0.50 Co mole fraction at 100 K, the first-neighbor Co-Co, Co-Pt, and Pt-Pt distances are 2.51-2.54 (+/- 0.01) angstrom, 2.57-2.58 (+/- 0.01) angstrom, and 2.64-2.68 (+/- 0.01) angstrom, respectively, which are all consistent with experimental values of around 2 nm NPs. The simulation results also show that the morphology, composition, and temperature play an important role in the atomic-scale structural properties of the Co-Pt bimetallic nanoparticles.