To further characterize the fibrils, we used Raman spectroscopy to investigate their molecular structures. As shown in Figure , each polymorph exhibits unique spectral fingerprints in the region between 1100 -1700 cm -1 . The most structurally informative Raman bands in the spectra occur in the Amide I, II, and III regions, located between 1600 -1700 cm -1 , 1500 -1600 cm -1 , and 1200 -1350 cm -1 , respectively. We examined these regions in detail to obtain structural information about the fibrils by performing spectral deconvolution analysis (see SI for details, Figures and). The results of this analysis are summarized in Table , which lists the Raman band assignments for the three polymorphs.