Quantitative nanometer-scale characterization of densification in fused silica via s-SNOM.

Fused silica is extensively used across various industries due to its superior properties, but densification can significantly alter its performance. Detecting these changes requires high spatial resolution, which challenges the limits of current testing methods. This study explores the use of scattering-type scanning near-field optical microscopy (s-SNOM) to analyze densification in fused silica through a combination of experimental techniques-atomic force microscopy-based infrared spectroscopy (AFM-IR) and s-SNOM-and computational methods, including first-principles calculations and the finite dipole model (FDM). The findings reveal that near-field phase signals are more accurate than amplitude signals in reflecting changes in densification. Building on these results, a quantitative model for characterizing densification in fused silica is proposed. These findings are compared with the results from the literature and comparison results show good concordance. This study introduces a nanoscale range precise, nondestructive method for assessing densification, offering a novel and reliable approach for characterizing point defects in fused silica.