Plastic properties of gold surfaces nanopatterned by ion beam sputtering

We review the mechanical properties of defective roughened surfaces with the major emphasis on nanoindentation work. We also report novel results in which force versus penetration curves and AFM images of the nanoindented surface are compared for a flat surface of Au(001) and an Ar(+) bombarded one, both with a high and a low flux of ions. We have found that bombarded surfaces yield at a lower stress than untreated flat ones. Surfaces bombarded at high flux show a large roughness and their yield point, marking the onset of surface plasticity, decreases with respect to that of the flat surface or of the surface bombarded with a low flux. The present results are compared with earlier work on nanoindented vicinal surfaces in which the sole surface modifications with respect to the flat surface were the presence of a high density of steps. It is concluded that a softening effect due to the bombardment-induced nanostructure of the surface dominates over the hardening one due to defect creation and interaction in the surface neighbourhood.