Contact Mechanics

Adhesion between surfaces at the atomic scale plays a crucial role in nanoscale systems and devices. While adhesion is commonly treated on the continuum level, we shed new light on the adhesion problem at the atomic scale. We employed molecular dynamics simulations to investigate the adhesion between two faceted Au nanoparticles. The simulations demonstrate that the approach of faceted particles, known as jump-to-contact, is mediated by extensive dislocation activity. Partial dislocations form near the first point of contact, propagate into the particle with trailing stacking faults, which are annihilated by the subsequent nucleation and motion of opposite partial dislocations on the same slip plane. This process is repeated, plane-by-plane as the contact line expands across the contacting facet. When the jump-to-contact process is complete, there is no dislocation debris left in the particles and the particle shapes are exactly as they were originally. Hence, jump-to-contact in faceted particles occurs through pseudoelastic, rather than true plastic, deformation. The simulation results show that standard adhesion models for spherical particles severely underestimate the energy gain due to formation of adhesive contact between faceted nanoparticles. We proposed a new model, estimate the contribution of elastic and edge energies to the energy of adhesion and show that the new model is consistent with the simulation results.