Nanomechanical scratching induced local shear deformation and microstructural evolution in single crystal copper

Shear deformation at the nanoscale has practical applications due to the ability of shear strains to significantly change the microstructures and textures of the deforming materials, and for material removal processes at this scale. Here we demonstrate nanomechanical scratching with atomic force microscopy (AFM) as a tool to impose large shear strains on nanoscale material volumes in single-crystal copper. Nano-scratching, with the process parameters and AFM tip geometry used here, resulted in material removal through the cutting mode. This mode enabled the use of stress and strain models, developed for bulk machining, to be applied for AFM cutting as well. The models for bulk-scale were used to predict the strains in the chip (γ ≈ 3.9) and in the surface (γ ≈ 4.6) and the depth of deformed subsurface. Detailed characterization of the scratch region with transmission electron microscopy (TEM) showed microstructural refinement comprising 0.2 μm wide dislocation cells in the chips that resemble features during shear deformation of copper single-crystals at bulk-scale. The subsurface also contained dislocation networks and stacking faults up to ~1.1 μm depth. These results highlight the unique ability of AFM for imparting local shear deformation in materials and studying its effects on the microstructure.