Plastic behaviour and deformation mechanisms in silicon nano-objects

Abstract

Physical properties of nano-objects differ from what they are in bulk materials when the size decreases down to the nanometre scale. This behavioural change, named size effect, also applies to mechanical properties and has been evidenced in various materials. For instance, at low temperature, bulk silicon is known to be a brittle material while silicon nano-objects exhibit a ductile behavior. Although mechanical properties of silicon have been intensively studied over the last decades, the origin of this remarkable brittle-to-ductile transition at small scales remains, however, undetermined. In this article, a study of the plastic behaviour of nano-pillars is reported. The main results obtained from the combination of numerical calculations and experimental compression tests followed by atomically-resolved transmission electron microscopy imaging are described. We discuss the possibility for perfect dislocations to dissociate at low temperature and the underrated role of shuffle partial dislocations in plastic deformation of silicon. The formation of unexpected extended defects in the {115} planes with increasing plastic strain, also appears as a key-factor leading to the transition between ductile and brittle regimes at small scales.