Fracture of nanoscale copper films on elastomer substrates

This letter describes the evolution of crack spacing in copper films (bonded to elastomer substrates) as a function of applied strain. Tension tests were conducted on cast poly(dimethylsiloxane) substrates coated with sputtered copper films with 200–600 nm thickness. Optical microscopy was used to measure the spacings between parallel cracks (normal to the tension direction) at various levels of applied strain in the range of 0.01%–10%. The measured relationships between applied strain and crack spacing are predicted by micromechanical models of behavior between cracks; the experiments indicate Gc?400–600 J/m2 with an implied defect spacing of ?100–600 ?m. These values are consistent with the theoretical work that is dissipated during necking instabilities during plastic deformation