Influence of local densification on microscopic morphology evolution during ion-beam sputtering of fused-silica surfaces.

Morphology evolution at microscopic scales has an inseparable relationship with surface material behaviors, especially during ultrasmooth surface fabrication. In this work, the influence of initially existing local densification on ion nanopatterning of a fused-silica surface is investigated. Our research results indicate that fused-silica surfaces will easily densify permanently under a compressive load, exhibiting an anisotropic surface at the nanoscale. During the subsequent ion-beam sputtering process, the densification-dependent sputtering would influence and even dominate surface morphology evolution, which is identified as being an important evolution mechanism. However, ion-induced relaxation mechanisms will overcome surface roughening in the absence of local densification, and an ultrasmooth surface with root mean square roughness down to 0.06 nm is obtained in our experiment.