Crystal morphology or crystal habit is one of the key crystallographic characteristics and can directly influence the properties of the crystalline material. Thus, it is important to control these features of crystals in order to avoid the unpredictable property alterations in the process of crystallization. Face indexing is one of the techniques used to get important information regarding a crystal’s morphology. Currently, the only developed method to experimentally determine crystal faces is the indexing by single crystal X-ray diffraction (SCXRD). However, limitations such as the requirement of high quality and specific size crystals, special instrumentation, and expert knowledge hinder the use of SCXRD with most crystals obtained under actual crystallization conditions. To circumvent this, we have developed a general method for the identification of the crystal faces using Raman spectroscopy. This method is based on the Raman polarizability, which affects the intensity of Raman peaks in the spectra depending on the crystal symmetry and the orientation of the sample. The procedure follows the steps of building a Raman library, validating the library against SCXRD data and the application of the library to the respective crystal systems. The developed method was successfully applied to three different epitaxial systems with a range of crystal sizes and quality. Acetaminophen (APAP) was grown as an overlayer crystal on D-mannitol (MAN), D-galactose (GAL), and xylitol (XYL) substrates. Six different face families for APAP and four different face families for each substrate were compiled into a Raman spectral library, which was then successfully used to identify the crystal faces of epitaxial pairs obtained under various experimental conditions.<br/>

Crystal face identification by Raman spectroscopy and application to the epitaxial growth of acetaminophen

256th National Meeting (2018)

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