Confinement-Induced Stable Amorphous Solid of Lennard–Jones Argon

Abstract

When a material is confined in a nanometer-scale pore, novel properties not seen in a macroscopic-scale material are expected. With this situation in mind, we carry out molecular dynamics (MD) simulation for the purpose of investigating the atomic configurations of Lennard–Jones (LJ) Ar solid in a pore of 3.4 nm in diameter. These results concerning the radial distribution function, Voronoi face parameters and bond-orientational order parameter show that the atomic structure of the confined Ar solid is non-crystalline (or in other words, amorphous) with a large number of Ar atoms having the local-icosahedral symmetry. The same kinds of the atomic configurations appears in bulk LJ glasses constructed via glass transition. However, there DOES exist a remarkable difference between these two cases. The amorphous structure in a bulk Ar glass easily crystallizes, after the annealing of 0.045–0.3 ns, into a closest-packed crystal (hcp, fcc or even a random stacking). On the other hand, the amorphous structure in a nanometer-scale pore remains unchanged on annealing even after 40 ns or longer. Our results of MD simulations strongly suggests that the amorphous structure in a confined Ar solid is ‘practically stable’ in the sense that no crystallization is observed during the time span of annealing.