Imaging molecular crystal polymorphs and their polycrystalline microstructures in situ by ultralow-frequency Raman spectroscopy.

Ultralow-frequency Raman spectroscopy that can measure vibrational bands at as low as ±10 cm(-1) has enabled facile in situ imaging of polycrystalline microstructures such as grains and grain boundaries with high polymorph specificity. We demonstrate this method by investigating microcrystals of two distinct polymorphs of 1,1'-binaphthyl using a microscope.