Deformation Behavior and Critical Shear Stress of Copper Nanocontacts Studied by In Situ Transmission Electron Microscopy

Tensile deformation of dislocation-free copper (Cu) nanocontacts (NCs) having widths of less than 6 nm was performed in a transmission electron microscope. The deformation behavior was observed In Situ via lattice imaging and the force acting on the NCs was simultaneously measured. The critical shear stress (CSS) for slip occurred in the NCs was estimated using the observed atomic configuration and the values of the forces. The relation of CSS with the minimum cross-sectional area of the NCs was investigated. The value of CSS was found to be at least two orders of magnitude higher than that observed for the well-known mechanism of dislocation-mediated slip in coarsegrained Cu. Furthermore, it was inferred that when the minimum cross-sectional width was larger than the critical value, i.e., 2.3 nm, deformation occurred via the introduction of dislocations into dislocation-free NCs and subsequent dislocation-mediated slip. When the minimum cross-sectional width was less than the critical value, the deformation mechanism transformed into simultaneous slip, i.e., no dislocation was mediated.