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

摘要

The thermal behavior of free and alumina-supported iron-carbon nanoparticlesis investigated via molecular dynamics simulations, in which the effect of thesubstrate is treated with a simple Morse potential fitted to ab initio data. Weobserve that the presence of the substrate raises the melting temperature ofmedium 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 theground state of smaller Fe nanoparticles ($N$ = 50-80). The main focus of ourstudy is the investigation of Fe-C phase diagrams as a function of thenanoparticle size. We find that as the cluster size decreases in the1.1-1.6-nm-diameter range the eutectic point shifts significantly not onlytoward lower temperatures, as expected from the Gibbs-Thomson law, but alsotoward lower concentrations of C. The strong dependence of the maximum Csolubility on the Fe-C cluster size may have important implications for thecatalytic growth of carbon nanotubes by chemical vapor deposition.