Residual electrical resistivity measurement was employed to study dislocation storage under tensile loading of freestanding electroplated Cu films (1 to 5µm grain size and 2 to 50µm thickness). The results indicated that the nature of thickness effects (strengthening or weakening) depended upon the underlying deformation mechanisms via the average grain size. A threshold grain size of about dg = 5µm was identified to distinguish grain size effects in thicker films from those in thinner films. For dg > 5µm, diminishing microstructural constraint with reduced thickness weakens the films due to dislocation annihilation near the free surface. For dg < 5µm, reduction of film thickness led to strengthening via grain boundary-source starvation.

Probing Thickness-Dependent Dislocation Storage in Freestanding Cu Films using Residual Electrical Resistivity. S.Chauhan, A.F.Bastawros: Applied Physics Letters, 2008, 93[4], 041901