The effects of annealing prior to dealloying on the mechanical properties of nanoporous gold microbeams

Freestanding nanoporous gold beams fracture during dealloying owing to volume shrinkage. This study illustrates that annealing after release, yet prior to dealloying, prevents failure during the selective dissolution step. Experiments in which annealing was performed at temperatures ⩽400 °C illustrate that permanent buckling of the freestanding solid alloy beams is required to prevent failure of the nanoporous beams during dealloying. In contrast, annealing of beams prior to release, or annealing temperatures ⩽200 °C (which do not cause permanent buckling deformation), do not mitigate dealloying failures. This work illustrates that the fabrication yield and the residual stresses (in the final nanoporous beams) correlate with the permanent buckling deflection of the alloy due to annealing, with the maximum yield (>95%) and the minimum residual stress (∼4–7 MPa) occurring for annealing at ∼300 °C. The present experimental results are used with elementary elastic buckling models to explain the critical temperature that produces permanent deflection, as well as discuss the mechanisms underlying the above phenomena.