Physics and nanofriction of alkali halide solid surfaces at the melting point

Abstract

Alkali halide (1 0 0) surfaces are anomalously poorly wetted by their own melt at the triple point. We carried out simulations for NaCl(1 0 0) within a simple (BMHFT) model potential. Calculations of the solid–vapor, solid–liquid and liquid–vapor free energies showed that solid NaCl(1 0 0) is a nonmelting surface, and that the incomplete wetting can be traced to the conspiracy of three factors: surface anharmonicities stabilizing the solid surface; a large density jump causing bad liquid–solid adhesion; incipient NaCl molecular correlations destabilizing the liquid surface, reducing in particular its entropy much below that of solid NaCl(1 0 0). Presently, we are making use of the nonmelting properties of this surface to conduct case study simulations of hard tips sliding on a hot stable crystal surface. Preliminary results reveal novel phenomena whose applicability is likely of greater generality.