Terahertz spectroscopy is a very exciting technique for the physico-chemical characterisation of organic molecular crystals (such as typical drug molecules). By probing the hydrogen bonding networks and the phonon modes in molecular crystals the technique has a very high sensitivity to the supramolecular structure in solids. We study a range of solid state modifications such as polymorphs, hydrates, solvates and cocrystals. By exploiting the very short acquisition times of THz-TDS we are able to study phase transitions in real time which allows us a better understanding of the mechanism behind such phenomena.
In addition to our work on crystalline materials we explore the applications of terahertz spectroscopy to characterise amorphous materials. While glasses do not exhibit distinct spectral features at terahertz frequencies it is possible to extract very useful information from THz-TDS measurements, such as the charge distribution.
Terahertz spectra of indomethacin. Amorphous indomethacin has a featureless spectra (black), while crystalline indomethacin exhibits distinct features in the terahertz region due to crystalline phonon modes.
Changes in terahertz spectra of carbamazepine (CBZ) with heating. Note the spectral changes from amorphous CBZ to crystalline CBZ and changes between crystalline form III and form I.