Evaluation of phase separation in glasses with the use of atomic force microscopy

Glass forming melts frequently exhibit liquid–liquid immiscibility resulting in phase separation. The chemical and spatial variation of phase separated morphologies in glasses can range from a few angstroms to microns, often requiring very high magnification for detection. Historically, phase separated glasses have been characterized by transmission electron microscopy (TEM). This technique is very time consuming and costly, requiring specialized equipment and training. Atomic force microscopy (AFM) provides an inexpensive alternative to TEM and has proven to be a powerful tool in the characterization of phase separation in glasses. AFM provides rapid and accurate evaluation of the type, degree and scale of phase separation in glasses down to the nanometer level. Using a combination of topographical and phase imaging AFM we were able to quantitatively determine the microstructures of phase separated glasses with a resolution down to 50 nm. Additionally we were able to quantitatively confirm the time dependence of the chemical segregation and growth processes for phase separation in glass by spinodal decomposition. This paper will present sample preparation techniques and results for evaluation of phase separation in alkali borosilicate and sodium silicate glass systems.