Evaluation of surface preparation methods for glass

In this study, methods of surface preparation by polishing, fiber-drawing, melt-casting and chemical etching were evaluated with x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) for a variety of alkali and alkaline earth aluminosilicate glasses. Freshly polished glass surfaces were exposed to a variety of chemical etchants (NaOH, NH₄OH and HF) and the resulting surface composition and morphology are reported. The polishing and etching parameters were optimized to obtain a smooth surface (root-mean-square (RMS) roughness of ≤3 nm) and a surface composition as close as possible to the bulk composition. In addition, glass melt and fiber surfaces were examined to investigate the effect of thermal processes on surface composition and morphology. It is shown that polishing can alter the surface composition of these multicomponent glasses, and that post-etching of the polished surface to expose the bulk composition is plagued by preferential leaching, contamination and/or roughening. The most significant conclusion is that there is a strong dependence of these surface compositional modifications upon the specific glass; even within specific glass systems, the polish/etch procedure must be modified to yield a surface with the bulk composition. On the other hand, the smoothness of fibers and melt-cast surfaces is ideally suited to AFM and depth profiling; their surface compositions can be close to the bulk values, but careful attention to the annealing conditions is required to achieve this.