Continuous thermodynamic-equilibriumglass transition in high-energy grain boundaries?

Recent simulations of silicon grain boundaries equilibrated at high temperatures and subsequently cooled to zero temperature have revealed a 'confined amorphous' equilibrium structure of uniform thickness for the highenergy boundaries while low-energy boundaries are crystalline. Here we demonstrate that, above the glass transition temperature T, these high-energy g boundaries undergo a reversible structural and dynamical transition from a confined amorphous solid to a confined liquid. By contrast with the bulk glass transition, however, this equilibrium transition is continuous and thermally activated, starting at T and being complete at the melting point T, at which g m the entire film is liquid. The coexistence of the confined amorphous and liquid phases in this two-phase region of less than 1 nm thickness is shown to have a profound impact on grain-boundary self-diffusion.