The mechanical properties and deformation behaviors of Cu with different grain sizes were investigated here by instrumented nano-indentation. Following the Hall-Petch relation, the hardness of Cu specimens increased as the grain size decreased. Dislocations were clearly observed in deformed regions around indent marks, indicating plastic deformation by dislocation formation and sliding. However, the hardness of electroless Cu films with an ultra-fine grain size of only 10nm dropped. Voiding at grain boundaries and triple grain junctions was observed as a consequence of grain-boundary sliding and grain rotation, which was expected as the dominant deformation mechanism resulting in the reduced hardness. The critical shear stresses for the initiation of plastic deformation in the Cu specimens with large grain sizes were close to the theoretical value and comparatively much lower for electroless Cu films with an ultra-fine grain size.

Grain Size Effect on Nanomechanical Properties and Deformation Behavior of Copper under Nanoindentation Test. S.Y.Chang, T.K.Chang: Journal of Applied Physics, 2007, 101[3], 033507 (8pp)