Raman spectroscopic measurements and imaging on sub-newton Berkovich and spherical imprints in fused silica

Abstract

This paper lays out best practices for evaluating and optimizing a Raman spectroscopy setup to ensure the collection of reliable spectral data and/or Raman images on indented glasses. The Raman spectroscopic measurements and imaging were conducted on residual imprints created with Berkovich and spherical probes at forces in the sub-newton range in fused silica. The capability of a conventional optical instrument for mapping spectral variations in sub-newton imprints on glasses is evaluated by studying the influence of the optical configuration (choice of microscope objective) on the spatial resolution of the spectroscopy setup. The spatial resolution was quantitatively assessed in Z profile measurements and qualitatively evaluated by mapping changes in spectral features and correlated densification within the indented regions of fused silica specimens. The paper discusses the importance of appropriately matching the analysis volume of the Raman spectroscopic setup with the size of the indentation-induced densification zone by demonstrating the detrimental effects a mismatch may have on accurately capturing the magnitude of spectral changes and correlated densification.