Chemical Mapping of Nanoparticle-Ligand Interfaces in Optical Nanocavities.

Understanding processes in photon-phonon scattering, absorption, and chemical reactions in optical nanocavities is important for single-molecule sensors, single-photon emitters, and photocatalysis. However, the influence of electromagnetic fields, charge transfer, and molecular geometry is challenging to probe by ensemble-averaged spectroscopic techniques over multiple nanocavities. Photoinduced force microscopy (PiFM), which measures photoinduced polarizability under infrared excitation of a sample in the nanocavity between the scanning probe microscopy tip and sample surface, is used here for simultaneous nanoscale topological and chemical characterization. First-principles density functional theory (DFT) simulations of the vibrational spectra of gold nanoparticle surfaces functionalized with benzenedithiol (Au-BDT) elucidate molecular orientation, charge transfer, and oxidation state for understanding molecular and adatom reconfiguration in optical nanocavities in response to external fields.