Roman Nowak

Abstract:

Our discovery of the "Current Spike" was first highlighted in the Letters to Nature Nanotechnology (Nowak et al. Vol.4 /2009/; Chrobak, Nowak, et al. Vol.6 /2011/) and offers an enhanced understanding of the link between nanoscale mechanical deformation and electrical properties. Our conclusions point to key advances in pressure-sensing, pressure-switching, and unique phase-change applications in next-generation electronics. It is a very encouraging demonstration of the way in which nanomechanics contributes to electronics and optoelectronics developments. The onset of plasticity is traditionally understood in terms of dislocation nucleation and motion. This study of nanoscale deformation has proven that initial displacement transient events occurring in metals are the direct result of dislocation nucleation. Our research shows that this is not always true: Instead of dislocation activity, nanoscale deformation may simply be due to transition from one crystal structure to another, as predicted for GaAs by our earlier atomistic calculations. The presented results lead to a major shift in our understanding of the elastic-plastic transition as well as inherent formation of a Schottky barrier in semiconductors under localized high pressures. The results showing the dramatic impact of crystal imperfections on the functional properties of GaAs motivated our further study into the onset of incipient plasticity in Si nanoparticles. Molecular Dynamics calculations and supporting experimental results reveal that the onset of plasticity in Si nanospheres with <130 nm diameter is governed by dislocation-driven mechanisms, in striking contrast to bulk Si where incipient plasticity is dominated by phase transformations. We established the previously unforeseen role of "nanoscale confinement" governing a transition in mechanical response from "bulk" to "nanovolume" behavior.