Nucleation, evolution, and growth dynamics of amorphous silica nanosprings

Abstract

The initial phases of amorphous silica nanospring formation via a vapor–liquid–solid mechanism are reported. The low temperature eutectic of Au–Si results in the formation of an asymmetrical shaped catalyst at the early stages of nanospring formation. As solid silica is formed below the Au–Si catalyst the system lowers its surface free energy and forms multiple amorphous silica nanowires beneath a common catalyst, as opposed to a single nanowire. The diameter of one of the nanowires forming the nanospring ranges between 10–20 nm. The difference in growth rates of the individual nanowires creates an asymmetry in the interfacial surface tension on the boundaries of the Au–Si catalyst/nanowires interface. Using Stokes’ theorem it is shown that there is a variable work of adhesion on the outer boundary of the Au–Si catalyst/nanowire interface of a nanospring, which is defined as an effective contact angle anisotropy. The anisotropic growth on the catalyst/nanowire boundary results in the nanowires coherently coiling into to a single, larger, helical structure with an overall diameter of 70–500 nm.