Catalyzed chemical polishing of SiO2 glasses in pure water

Daisetsu Toh, Pho Van Bui, Ai Isohashi, Naotaka Kidani, Satoshi Matsuyama, Yasuhisa Sano, Yoshitada Morikawa, and Kazuto Yamauchi, "Catalyzed chemical polishing of SiO2 glasses in pure water", Review of Scientific Instruments 90, 045115 (2019), https://doi.org/10.1063/1.5090320.
A catalytically assisted etching system was developed for the ultra-precision fabrication of optical components, such as X-ray mirrors and extreme-ultraviolet mask blanks. This study demonstrates that an atomically smooth surface with a sub-Angstrom root-mean-square roughness could be achieved on a SiO2 glass substrate using pure water and Pt as the etching solution and catalyst, respectively. Density functional theory calculations confirmed that the mechanistic pathway was involved in catalyzed hydrolysis. The significant roles of the catalyst were clarified to be the dissociation of water molecules and the stabilization of a meta-stable state, in which a hypervalent silicate state is induced, and the Si-O backbond is elongated and loosened. To confirm the role of the catalyst, the Pt metal was replaced by Au, and the observed drastic difference in the removal rate was attributed to the degree of stabilization of the metastable state.