Boron nitride nanoresonators for phonon-enhanced molecular vibrational spectroscopy at the strong coupling limit

Infrared spectroscopy is a powerful tool for characterizing materials based on their specific vibrational fingerprints. However, its ability to characterize small amounts or thin layers of molecules is limited by their extremely small infrared absorption cross-sections. This limitation can be overcome by surface-enhanced infrared absorption spectroscopy (SEIRA), which exploits the field enhancement provided by plasmon polaritons on thin metal films or resonant metallic nanostructures. Now, Rainer Hillenbrand from CIC nanoGUNE in San Sebastian (Spain) and co-workers have developed highly sensitive phonon-polariton resonators for SEIRA detection, based on hexagonal boron nitride ribbons, which exhibit quality factors much higher than their plasmonic counterparts. They demonstrated phonon-enhanced molecular vibrational spectroscopy with sensitivity down to femtomolar levels, approaching the strong coupling limit.