PNNL

Abstract

Shear deformation at the nanoscale has practical applications due to the ability of shear strains to cause significant changes in the microstructures and textures of the deforming materials, as well as for material removal processes at this scale. In this study, we demonstrate nano-scratching with atomic force microscopy (AFM) as a tool to impose large shear strains on nanoscale material volumes of a single-crystal copper workpiece. Nano-scratching, with the process parameters and AFM tip geometry used in this study, resulted in material removal through the cutting mode. This mode enabled the use of stress and strain models, developed for the bulk machining of materials, to be applied for AFM cutting as well. We show that the models for bulk-scale can be used to predict the strains in the chip (? ˜ 3.9) and the surface (? ˜ 4.6) together with the depth of deformed subsurface. Detailed characterization of the scratch region with transmission electron microscopy (TEM) showed microstructural refinement consisting of 0.2 µm wide dislocation cells in the chips that resemble the features during shear deformation of copper single-crystals at the bulk-scale. The subsurface also contained dislocation networks and stacking faults at depths down to ~ 2 µm. These results highlight the unique ability of AFM for imparting local shear deformation in materials and studying its effects on the microstructure.