Probing thickness-dependent dislocation storage in freestanding Cu films using residual electrical resistivity

Residual electrical resistivitymeasurement is employed to study dislocation storage under tensile loading of freestanding electroplated Cufilms (1–5μm grain size and 2–50μm thickness). The results indicate that the nature of thickness effects (strengthening or weakening) depends on the underlying deformation mechanisms via the average grain size. A threshold grain size of about dg=5μm is identified to distinguish grain size effects in thicker films from those in thinner films. For dg\u3e5μm, diminishing microstructural constraint with reduced thickness weakens the films due to dislocation annihilation near the free surface. For dg\u3c5μm, reduction of film thickness leads to strengthening via grain boundary-source starvation