Finite-Size Effects in Nanoscale Lattice-Mismatched Lubricant Droplets

In this work we study finite-size effects of nanoscale lubricant 2D droplets (or islands) by molecular dynamics. A small lubricant droplet is confined between two 2D crystalline layers; the bottom layer is static, while the top one slides rigidly. Simulations show that small nearly-lattice-matched islands can snap to commensuration entirely, changing their initial particleparticle distance ap to match the closest-in-registry lattice spacing ab so as to place epitaxially each lubricant particle in one energetically convenient hollow site of the bottom surface. For strongly mismatched islands instead, a solitonic pattern can remain trapped within the island, which deforms to a triangular-like shape. An overall droplet rotation during the snapping process is also observed under certain circumstance. Studying islands dragging phenomena, we find that commensurate snapped to commensuration droplets remain pinned to the bottom layer even when the top layer advances; while, when solitons are present and under favorable circumstances, the lubricant advances at some intermediate speed. Advisor: Prof. Nicola Manini Co-Advisor: Prof. Giuseppe Santoro