Acoustic Graphene Plasmon Nanoresonators for Field-Enhanced Infrared Molecular Spectroscopy

Field-enhanced infrared molecular spectroscopy has been widely applied in chemical analysis, environmental monitoring, and food and drug safety. The sensitivity of molecular spectroscopy critically depends on the electromagnetic field confinement and enhancement in the sensing elements. Here we propose a concept for sensing that consists of a graphene plasmonic nanoresonator separated from a metallic film by a nanometric spacer. Such a resonator can support acoustic graphene plasmons (AGPs) that provide ultraconfined electromagnetic fields and strong field enhancement. Compared with conventional plasmons in graphene, AGPs exhibit a much higher spontaneous emission rate (reaching values up to 1 X 10(8)), higher sensitivity to the dielectric permittivity inside the AGP nanoresonator (the figure of merit is higher by a factor of 7), and a remarkable ability to enhance molecular vibrational fingerprints of nanoscale analyte samples. Our work opens novel avenues for sensing of ultrasmall volumes of molecules as well as for studying enhanced light-matter interactions, e.g., strong coupling applications.