Geometry and surface state effects on the mechanical response of Au nanostructures

A study of ultra-thin gold films and thin-walled nanoboxes has confirmed that length scales in terms of dislocation spacing can predict flow stress. Initial stages of deformation conform to linear hardening with average dislocation spacing controlled by the number of geometrically necessary dislocations in a pile-up. Later stages of deformation exhibit parabolic behavior with Taylor hardening interpreted in terms of a dislocation density described by the total line length of prismatic loops per unit volume. Comparisons of 20 and 40 nm thick planar films could be made to 205 nm high hollow gold nanoboxes with a wall thickness of 24 nm. These highly constrained, ultra-thin planar films demonstrated increased hardness from about 2 to 10 GPa with strains of 20 percent while less constrained nanoboxes increased from 0.8 to 4 GPa for the same strain magnitude.