Plane-strain bulge test for nanocrystalline copper thin films

Free-standing nanocrystalline Cu films with grain size around 39 nm are fabricated by thermal evaporation and characterized by the plane-strain bulge test. Young’s modulus and yield stress at a 0.2% offset are about 110–130 GPa and 400 MPa, respectively. Results show that the strength of the n-Cu films is largely independent of film thickness at a strain rate less than 10−5 s−1. No grain growth is observed and the predominant plastic deformation mechanism is grain boundary sliding accompanied by dislocation mechanisms.