Precision Measurements Of Material-Removal Rates In Superpolishing Sapphire

As we demonstrate, sapphire can be polished by means of colloidal SiO2 (7 nmφ) in water by direct contact to a tin lap to a residual roughness better than 0.3 nm Rz measured with a Talystep profilometer. We use the superpolishing mechanism itself for producing microscopically smooth grooves which can serve for a precision measurement of the very small removal rates intrinsic to the superpolishing process. In order to explain the superpolishing process, we propose the model of hydrothermal wear.