Dependency of the type of oxygen bonds on the roughness of classically manufactured fused silica surfaces

Glass polishing is a complex process where the formation of the final surface results from several quite different mechanisms – pure mechanical abrasion, wear-induced fretting, flow-induced surface smoothing, and glass modification and removal via chemical reactions. The aim of the study is thus to analyse the chemical composition and surface roughness throughout the entire classical optics manufacturing process of fused silica, which includes the production steps of cutting, grinding or lapping, and polishing, using X-ray photoelectron spectroscopy and atomic force microscopy. It is shown that the analytical results are in good accordance with the polishing theory initially suggested by Beilby, Bowden and Hughes in the 1920s and 1930s. The decomposition of the oxygen peak from the detail XPS spectra allowed a subdivision of Si–O bonds into silicon dioxide and silanol such as Si–OH or Si(OH)4, which enabled a direct correlation between the SiO2 and silanol concentration and the surface roughness occurring for the particular manufacturing steps.