Effects of surface microtopography on material removal and ultra-smooth surface creation processes in ultraviolet-induced nanoparticle colloid jet machining

Ultraviolet-induced nanoparticle colloid jet machining is a damage-free ultra-smooth surface polishing technology, which can realize atomic level material removal by utilizing the interface reaction between workpiece surface and nanoparticles in colloid jet beam under the catalysis of ultraviolet (UV) light. Due to the difference of chemical activity of atoms at different microstructures ("plane", "peak" and "valley" structure), the interfacial reaction degree between these atoms and nanoparticles in colloidal environment and the difficulty to remove those surface atoms are also different. To investigate the effects of surface microtopography on material removal and ultra-smooth surface creation processes in UV-induced nanoparticle colloid jet machining, first principle simulations of the interfacial reaction between the TiO2 nanoparticle and Si "plane", "peak" and "valley" structures have been done. Adsorption experiments and ultra-smooth surface polishing experiments were carried out to verify the rationality of the simulation results. The results indicate that the interface reaction between the "peak" structure and TiO2 nanoparticle is the most likely to occur, and the "valley" structure is the most difficult to occur. After the TiO2 nanoparticle being chemically bonded on the Si surface, the atoms on the "peak" structure are the easiest to be removed, and that of the "valley" structure are the most difficult to be removed. An ultra-smooth Si workpiece with surface roughness of Sq 0.49 nm has been obtained by UV-induced nanoparticle colloid jet machining. The power spectral density (PSD) results show that the Si workpiece has been gradually changed from a progressive surface to a fine surface, and has been smoothed in the wavelength range of 0.25–10 µm.