Abstract
The fundamental behavior of materials in sliding contact is challenging to determine since the interface is normally hidden from view. Using a custom microfabricated device, we conducted in situ, ultrahigh vacuum transmission electron microscope measurements of silver-silver crystalline nanocontacts under combined tension and shear, permitting simultaneous observation of contact forces and contact width. Here, we find the Ag-Ag contacts exhibit only limited shear-induced junction growth, unlike the larger growth seen at macroscales. The difference arises from the nanocontacts’ high strength. The von Mises stresses at yield points approach the ideal strength of silver, attributed to the nearly defect-free nature and small size. The results are consistent with recent predictions that nanocrystalline fcc metals yield via interfacial amorphization. The contacts separate unstably, with pull-off forces well below predictions for rupture under pure tension. This provides in situ evidence that shear reduces nanoscale pull-off forces, consistent with theoretical predictions for this effect.