Plasticity responses in ultra-small confined cubes and films

Nanoindentation-induced dislocation emission at 5-7 nm displacements in ultra-thin films (12-33 nm) and nanocubes (40-60 nm) is used to examine deformation and plasticity models. Using the Tabor estimate, this displacement corresponds to a plastic strain of 3-5%. Load-displacement curves produced using nanoindentation show evidence of discretized, Burgers vector-length displacement steps, or excursions, which can be associated with individual dislocation emission events. Using these displacement steps and the residual plasticity present on unloading, theoretical hardening models are developed. Linear and parabolic hardening approaches are compared for ultra-thin films of nickel, cobalt, and Permalloy (Ni₈₀Fe₂₀), and also for silicon nanocubes. It is determined that the linear hardening model can predict the early trends of the experimental data while parabolic hardening may be more appropriate at later stages.