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 G(c) similar to 400-600 J/m(2) with an implied defect spacing of similar to 100-600 mu m. These values are consistent with the theoretical work that is dissipated during necking instabilities during plastic deformation. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3268458]