6. Conclusions

Experimental procedures based on atomic force microscopy to measure hardness, friction and wear, and the shear strength of metallic surfaces at the nanometer scale have been presented. AFM indentation was used to quantitatively and reproducibly determine the hardness and deformation mechanisms of Au(111), Pt(111), and a Pt57.5Cu14.7Ni5.3P22.5 metallic glass with unprecedented resolution in imaging and force curves. At the nanometer scale, the plastic deformation of singlecrystalline metal surfaces is accommodated over large distances and mediated by dislocations. For Pt57.5Cu14.7Ni5.3P22.5 metallic glass, the nanometer-scaled plastic deformation is continuous and localized around the indenter; this contrasts with the observation of serrated flow at the μm scale.

AFM scratch testing was used to demonstrate the transitions between different wear regimes on Au(111) during single-asperity sliding contact. The coefficient of friction is found to increase with the severity of wear (from adhesive to abrasive). In the low load regime, wear is governed by adhesive effects, although in this regime the first dislocation lines could be observed. In the transitional regime, the formation of surface ripples was observed with the spacing between ripples increasing with the load. This regime corresponds to a transition from adhesive to abrasive wear, in which case materials start to be displaced ahead of the AFM tip. At larger loads, plowing is the governing mechanism. In this regime, the topography images are featureless, with exception of pileups at the side of the scanned area.

Atomic stick-slip images recorded on an Au(111) surface with a gold-coated tip were used to determine the shear strength of a metallic junction. By statistical analysis, we determined the periodicity of atomic stick-slip. Expectedly, it is found to correspond to the interatomic distance of gold.
