R-plane monocrystalline sapphire surface damage evolution under single grit scratching

High-quality and low damage processing of R-plane sapphire substrates is a crucial prerequisite for improving the performance of advanced LED devices. In order to explore the surface damage evolution mechanism during its dynamic removal process, this research investigated the surface damage evolution of R-plane sapphire scratched along the [ direction through Rockwell scratch experiments. The experimental results indicate that the ductile removal regime occurs within a load range of 1.32 N to 8.02 N. By utilizing AFM and SEM surface morphology characterization methods, the damage evolution process of R-plane sapphire was observed and analyzed. And theoretical models for elastic-plastic stress field analysis and Finite Element Method (FEM) simulation models are established, jointly revealing the mechanism on surface damage evolution of R-plane sapphire with the nucleation and propagation of Hertzian cracks, median cracks, transverse cracks, and surface radial cracks. Based on the theoretical calculation results, as the normal load increases, the maximum tensile stress rises from 0.536 to 1.577 in the xoy plane, with this peak value shifting to a location away from the direction of scratching. A consistent increasing trend is observed in the xoz plane, where the tensile stress grows from 0.447 to 0.819 with the peak stress consistently occurs at x/b = 0.36 across all loads. Moreover, the FEM results for maximum principal logarithmic strain show that sapphire undergoes a peak deformation of 15.3% during scratching, which is localized on both sides of the formed groove. Finally, a surface damage evolution model for R-plane sapphire was proposed.