The Effects of Confined Core Volume on the Mechanical Behavior of Al/a-Si Core-Shell Nanostructures

The mechanical behavior of novel Al/a-Si core-shell nanostructures (CSNs) is studied using instrumented nanoindentation to investigate the role that the confined core volume plays on the mechanical response of these structures. The CSNs are fabricated from truncated hemispherical Al nanodots with 100, 200, and 300 nm base diameters, which are then conformably coated with a-Si. CSNs with the smallest core diameter, and therefore the smallest confined core volume, have a unique load-displacement behavior characterized by nearly complete recovery of deformation beyond the elastic limit, which is enabled by dislocation activities within the confined Al core. In conjunction with this deformation recovery, discontinuous indentation signatures known as “load-drops” and “load-jumps” are observed during loading and unloading, respectively. As the size of the confined core volume increases, these indentation signatures are suppressed and the deformation-resistant properties are reduced. Supporting molecular dynamics simulations show that a smaller core volume results in a larger back-stress developed in the core during indentation, which further correlates with improved dislocation removal from the core after unloading. This complementary experimental and modeling investigation provides insight into the mechanisms that contribute to the unique mechanical properties of Al/a-Si CSNs