Atomistic investigation of the effect of contact condition on frictional properties of nanowire

At the nanoscale, the interfacial shear strength is often determined without considering the uncertainty in the contact condition. The contact between flat surfaces is particularly obscure because of their atomic-level irregularities. This study conducts molecular dynamics simulations to investigate the contact condition between nominally flat surfaces. Simulations using nanowires with flat and rough surfaces are conducted to assess the interfacial shear strength involved with the contact condition. The simulation result shows that the interfacial shear strength of the nanowire with a flat surface is 1.9 MPa. Although a rough nanowire has a much smaller real contact area than the flat nanowire, the rough nanowire exhibits similar frictional force and much greater shear strength (22.8 MPa) compared to the flat nanowire. The distance between the nanowire and the substrate is examined to reveal the mechanism, and the rough nanowire showed a shorter distance than the flat nanowire. The shorter distance is attributed to the concentrated normal force at the contact junction and causes a high frictional force per contact area because of its larger potential energy barrier. The interfacial shear strength can feasibly be underestimated for a nominally flat-facet nanowire.