NANOMECHANICAL PROPERTIES OF AU(111), AU(001), AND AU(110) SURFACES

Using the interfacial force microscope in an indentation mode, we have quantitatively investigated the mechanical properties for the (111), (001), and (110) surfaces of Au single crystals. Nanoscale indentation s of wide, atomically flat terraces provide a measure of the nanomecha nical properties of Au in the absence of bulk and surface defects. The elastic indentation modulus for the (111) surface was found to be 36% greater than for the (001) and 3% greater than for the (110) surfaces . These results are compared to earlier theoretical predictions of the effect of anisotropy on indentation based on continuum mechanics and atomistic simulations. Additionally, we have quantified the yield poin t of the three crystal orientations by measuring the stress at which i nitial plastic deformation occurs. By resolving the applied stresses o n {111} slip planes, we have estimated maximum shear stresses at the y ield point. For each orientation, plastic deformation occurred when th e maximum resolved shear stress reached approximately 1.8 GPa on all { 111} planes that appeared to contribute to deformation. Based on this estimate, we propose that the critical resolved shear stress for plast ic indentation of Au is 1.8 GPa and that the yield criterion is that t his stress be attained on all {111} slip planes noncoplanar with the s urface.