Size dependent phase diagrams of Nickel-Carbon nanoparticles

TL;DR

This study calculates size-dependent phase diagrams of nickel-carbon nanoparticles, revealing how carbon incorporation influences melting and stability, which impacts nanotube growth mechanisms.

Contribution

It introduces a size-dependent phase diagram model for Ni-C nanoparticles using a tight binding and Monte Carlo approach, highlighting surface effects on melting.

Findings

Carbon lowers eutectic temperature in nanoparticles.

Size affects phase stability and melting behavior.

Surface carbon incorporation influences nanoparticle phases.

Abstract

The carbon rich phase diagrams of nickel-carbon nanoparticles, relevant to catalysis and catalytic chemical vapor deposition synthesis of carbon nanotubes, are calculated for system sizes up to about 3 nanometers (807 Ni atoms). A tight binding model for interatomic interactions drives the Grand Canonical Monte Carlo simulations used to locate solid, core/shell and liquid stability domains, as a function of size, temperature and carbon chemical potential or concentration. Melting is favored by carbon incorporation from the nanoparticle surface, resulting in a strong relative lowering of the eutectic temperature and a phase diagram topology different from the bulk one. This should be taken into account in our understanding of the nanotube growth mechanisms.