Micro-pillar measurements of plasticity in confined Cu thin films

Sputtering was utilized to deposit polycrystalline Cu and CrN films sequentially onto Si(100) substrates, forming specimen assemblies in which predominantly 〈111〉〈111〉 oriented Cu thin films of varying thicknesses were confined between Si and CrN. Cylindrical micro-pillars of CrN/Cu/Si(100) were fabricated through focused ion beam milling, with the interfaces either normal to the axial direction or at an inclination of 45°. Axial compression loading of the micro-pillars produced extensive plasticity within the thin Cu interlayers in both cases, but with distinctly different responses involving combined compression and shear when the interfaces are normal to the compression axis and constrained shear when the interfaces are inclined. Significant size effects were observed, offering new experimental evidence of scale-dependent plasticity for thin film layers, and new experimental test cases for non-local plasticity theories.