Strain-hardening in submicron silicon pillars and spheres

Measurements of submicron spheres and pillars of silicon single crystals have exhibited a strain-hardening capacity equal to or greater than their metallic counterparts. Stress-strain characteristics are reported for diameters ranging from 40 to 400 nm. Evaluations were performed with nanoindentation-based atomic force, scanning and transmission electron microscopies. Values of strain-hardening exponents up to unity in nanospheres are attributed to a size effect variation on the rate of increase of contact area with deformation. A surface-mediated dislocation nucleation concept is shown to be consistent with length scale effects partially modified by geometry as well as size. It is proposed, but not proven, that the modification relates to greater constraint in compact spheres as opposed to tall pillars.