Theoretical study of the thermal behavior of free and alumina-supported Fe-C nanoparticles

TL;DR

This study uses molecular dynamics simulations to explore how substrate support influences the thermal properties and phase behavior of iron-carbon nanoparticles, revealing size-dependent shifts in melting points and phase diagrams relevant to nanotube growth.

Contribution

It provides new insights into the size-dependent thermal and phase behavior of Fe-C nanoparticles on alumina substrates using molecular dynamics simulations.

Findings

Substrate raises melting temperature of Fe-C nanoparticles by 40-60 K.

Smaller nanoparticles have ground states influenced by the substrate.

Eutectic point shifts to lower temperatures and C concentrations with decreasing nanoparticle size.

Abstract

The thermal behavior of free and alumina-supported iron-carbon nanoparticles is investigated via molecular dynamics simulations, in which the effect of the substrate is treated with a simple Morse potential fitted to ab initio data. We observe that the presence of the substrate raises the melting temperature of medium and large $Fe_{1-x}C_x$ nanoparticles ($x$ = 0-0.16, $N$ = 80-1000, non- magic numbers) by 40-60 K; it also plays an important role in defining the ground state of smaller Fe nanoparticles ($N$ = 50-80). The main focus of our study is the investigation of Fe-C phase diagrams as a function of the nanoparticle size. We find that as the cluster size decreases in the 1.1-1.6-nm-diameter range the eutectic point shifts significantly not only toward lower temperatures, as expected from the Gibbs-Thomson law, but also toward lower concentrations of C. The strong dependence of the maximum C solubility on the Fe-C cluster size may have important implications for the catalytic growth of carbon nanotubes by chemical vapor deposition.