Analysis on formation mechanism of ultra-smooth surfaces in atmospheric pressure plasma polishing

Abstract

Atmospheric pressure plasma polishing (APPP) is developed for the final finishing of high quality ultra-smooth surfaces. To improve surface quality, formation mechanism of ultra-smooth surfaces in APPP is studied. Quantum chemistry simulation is used to investigate the interaction between atoms. Simulation of single Si-F bonding process indicates 0.2 eV difference of binding energy between convex and concave models, which reflects the reaction probability of convex structure is higher than that of concave structure. By comparing the spatial atomic configuration and species diffusion path, it is also demonstrated convex topography should be removed faster than concave topography. So roughness of optical surfaces can be reduced further to form ultrasmooth surfaces. And experimental results accord well with theoretical analysis. Detected by atomic force microscopy every 40 s, the average maximum height of surface is testified to decrease faster than the maximum depth obviously, which makes the whole surface going toward a new equilibrium status with lower roughness. Another experiment proves the average surface roughness decreases from Ra 4.529 to 0.926 nm after 100 s continuous machining. And the stereo images also indicate obvious improvement of surface topography. Moreover, free outmost electron is proved to be helpful to promote chemical reaction by simulation, so fresh surfaces may be more favorable for APPP which makes sample preparation more purposeful.