Achieving ultra-smooth and damage-free surface through understanding the material removal mechanism of the modification layer via molecular dynamics simulation and experiment

With the continuous advancement of technology, the manufacturing standards for optical components have become increasingly stringent. Due to variations in material properties, achieving satisfactory surface roughness on certain materials remains challenging. Researchers have employed surface modification techniques to alter the properties of substrate surfaces, resulting in enhanced polishing precision on modification layers. However, subsequent investigations have revealed that during the precise figuring of these ultra-smooth, damage-free modification layers, a significant number of defect structures emerge on the surface, leading to a marked increase in surface roughness and severely limiting ultimate machining precision. To address these issues, this study focuses on ion beam figuring (IBF) as a case study. It first elucidates the mechanisms of material removal from the modification layer surface during IBF through microscopic characterization techniques and molecular dynamics (MD) simulations. Microscopic analysis indicates that the morphology of the substrate significantly influences the properties of the modification layer. The MD simulation results demonstrate that variations in the properties of the modification layer contribute to discrepancies in local sputtering yields, which in turn lead to the formation of surface defects. Finally, based on these findings, a method for achieving ultra-smooth, damage-free fabrication of modification layer surfaces is proposed, and its feasibility is experimentally validated. The results demonstrate that modification layers grown on smooth, defect-free substrates exhibit superior quality, with surface roughness remaining below 0.2 nm RMS after figuring, while maintaining an ultra-smooth and damage-free state.