In-plane characterization of structural and thermodynamic properties for steps at faceted chemically heterogeneous solid/liquid interfaces

We present a methodology for studying steps at faceted chemically heterogeneous solid/liquid interfaces, based on equilibrium molecular-dynamics simulations. The methodology is applied to a faceted Al(111)/Pb(liquid) interface (750 K, ambient pressure), yielding a direct calculation of step free energy and extensive atomic-scale characterization for the interfacial layer containing the step. We demonstrate the power spectrum of the equilibrium step fluctuations obeys the capillary wave theory, and the calculated step free energy is consistent with experimental measurement [Acta Mater 2001; 49:4259]. The step fluctuations are identified to be governed by the attachment/detachment limited kinetics. Furthermore, we characterize the step by calculating the in-plane profiles of density, concentration, potential energy, pressure components and stresses. The fundamental properties of interface solid and interface liquid extracted from the in-plane profiles show orders of magnitudes difference in comparing with those predicted from the bulk Al-Pb alloy phase diagram. Several excess step properties are also determined along with defining a generalized Gibbs dividing surface.