Mechanical deformation of high-purity sputter-deposited nano-twinned copper

Near classical yield points were reproducibly observed at room and liquid nitrogen temperatures during tensile deformation of 170 μm thick, high-purity copper foils synthesized by magnetron sputter deposition. Uniformly distributed mobile dislocations introduced by rolling to ∼20% reduction in thickness eliminated the yield point at both temperatures. The experimental observations clearly demonstrate that the observed yield-point behavior is a direct result of the very low initial dislocation density in these sputtered films as expected for “ideal” nanoscale microstructural materials.