Characteristics of hydrolyzed layer and contamination on fused silica induced during polishing

Optical polishing is a chemo-mechanical process which can induce a near-surface hydrolyzed layer with contamination. To date, it is not clear whether the contaminants in the hydrolyzed layer are present as a uniform dopant or as discrete particles. The purpose of the present work is to try to clarify this contamination form. A field emission scanning electron microscope (FE-SEM) was used to determine the micro-topography and composition mapping of the polished fused silica. The relative density of the hydrolyzed layer and the bulk has been assessed using a combination of focused ion beam (FIB) milling and FE-SEM. The results suggest that the dopant contamination is located in the upper layer (tens of nm thick), which has a lower density compared to the bulk. Also, discrete contaminant ‘islands’ are present in the hydrolyzed layer.