Size dependence of mechanical properties of gold at the micron scale in the absence of strain gradients

Classical laws of mechanics hold that mechanical properties are independent of sample size; however, results of experiments and molecular dynamics simulations indicate that crystals exhibit strong size effects at the sub-micron scale. In experimental studies, the size effect can be explained by strain gradients. Atomistic simulations suggest that the yield strength depends on the size even without strain gradients and scales with the sample size through a power relationship. We address these different approaches to the size dependence of mechanical properties. Results of uniaxial compression experiments on gold at the sub-micron scale, without stress/strain gradients, are presented here. Freestanding Au cylinders are created by two unique fabrication processes and subsequently compressed in the Nanoindenter with a flat punch. Compressive stress, strain, and stiffness of the pillars are determined. Test results indicate a significant flow stress increase, up to several GPa. These high strengths appear to be controlled by dislocation starvation, unique to small crystals.