Ultrasmooth metal thin films on curved fused silica by laser polishing

The fabrication of atomically smooth metal films on supporting oxides is a quite demanding task, since most physical vapor deposition methods used on metals do not work properly on oxide substrates. Here, we report an alternative procedure, based on performing laser polishing of a fused silica substrate before depositing the metallic thin film. This reduces the RMS surface roughness of fused silica by ca. 33%, and increases the maximum grain size of the metallic film from 200 nm to 1200 nm. The method has been applied to a fused silica parabolic lens, which has been coated with a graphene-terminated Ru thin film. The reduction of surface roughness caused by laser polishing leads to the formation of ultrasmooth Ru thin films. Crystallinity and subnanometer roughness of the metal coating are demonstrated by the observation of He diffraction from a macroscopically curved surface.