Chemically tempered glass refers to glass in which compressive stress is applied to the surface by utilizing the "stuffing effect" (a phenomenon in which the network structure of glass is compressed) by infiltrating atoms with a large ionic radius.Due to its resistance to cracks and scratches, it has become explosively popular in recent years as a cover glass for smartphones and tablets.

　On the other hand, it was not possible to evaluate the strength of chemically strengthened glass with high spatial accuracy.The strength of chemically strengthened glass is greatly affected by the residual compressive stress and its spatial distribution, but from the viewpoint of microstructure, the conventional inspection method has a limit of several mm to cm.

　So far, the researchers have been conducting research to characterize the glass structure by a measurement method called Raman spectroscopy.This time, we succeeded in deriving a local evaluation formula of residual stress based on microscopic Raman spectroscopy and stuffing effect by utilizing this knowledge.Since this evaluation formula includes information on the composition of glass and the network structure, the spatial distribution of residual compressive stress can be obtained with an accuracy of μm.This makes it possible to evaluate the residual stress distribution of commercially available chemically strengthened glass with high spatial resolution in a non-destructive and non-contact manner using laser light.

　It is thought that this method can clarify the origin of the strength of tempered glass, and it will be possible to design more precise tempered glass.In the future, it can be said that this is a result that is expected to be applied to the development and quality control of glass that is not "hard to break" but "not breakable".

Paper information:[Communications Physics] A novel method for stress evaluation in chemically strengthened glass based on micro-Raman spectroscopy