Surface cleaning and etching of rare-earth doped phosphate glass

The surface reactions of phosphate glasses are important for the processing and application of photonic devices, biomedical materials and conventional optical components. Of particular concern are the leaching of optically-active dopant species, surface layer formation and roughening during polishing, cleaning and other fabrication processes. In this study, the effects of various cleaning treatments, and both acid and base etching, were evaluated using surface analytical techniques (XPS, AFM). It is shown that in these phosphate glasses, the aluminum and rare-earth oxides have limited aqueous solubility, whereas the phosphate network is soluble over a wider range of pH. Thus, under those conditions where polishing damage can be removed by etching the surface, a localized precipitation of rare-earth oxides occurs which influences the final roughness and surface composition. Conversely, under conditions where this precipitation can be eliminated, an in-depth leaching of the surface occurs. These aqueous surface reactions were similar for both the optically-active and passive IOG-1 glasses. An optimized surface preparation method is described.