Deformation mechanism and depth modelling in ultrasonic vibration-assisted AFM tip-based nanoscratching of indium phosphide crystals

Precise nanogroove fabrication on indium phosphide (InP) crystals requires controllable material removal while avoiding excessive subsurface damage. Normal ultrasonic vibration-assisted nanoscratching (NUVAN) provides a promising route for improving atomic force microscope (AFM) tip-based nanomachining; however, the relationship among processing parameters, groove formation, chip removal and subsurface damage evolution remains insufficiently understood. In this study, AFM tip-based conventional scratching and NUVAN experiments were performed on single-crystal InP (100) along the < 110 > direction, in combination with molecular dynamics simulations, cross-sectional transmission electron microscopy (TEM) characterization and theoretical modelling. The results show that normal ultrasonic vibration changes the tip–sample interaction from sustained extrusion to intermittent contact, producing deeper grooves under the same nominal scratching force and promoting chip fragmentation and evacuation. Cross-sectional TEM observations reveal that both scratching modes induce plasticity-dominated subsurface deformation, including lattice distortion, dislocations, stacking faults, nanotwins and localized amorphization. Under NUVAN, more pronounced nanotwin formation and the retention of local nanocrystalline domains within the amorphous matrix suggest a modified strain accommodation pathway under cyclic loading. A damage index was introduced, confirming that NUVAN significantly reduces the degree of subsurface damage per unit material removal volume. Finally, a groove-depth prediction model was established by coupling elastic recovery, strain-rate effect, cyclic hardening, contact intermittency and vibration energy efficiency. This model links the nominal scratching force and normal vibration amplitude to the final groove depth, providing a processing-oriented basis for controllable NUVAN of brittle semiconductor materials.