Design of Functionalized Tip Driven by Molecule-Plasmon Coupling

Abstract

The sensitivity of plasmon-enhanced spectroscopy (PES) fundamentally arises from the near-field enhancements within plasmonic nanocavities. To further advance PES, we utilized a molecule with exciton modes that are sensitive to the excitation wavelength to functionalize the metal tip. Our findings reveal that exciton modes play a dominant role in shaping the near-field patterns. Specifically, "hot spots" within the exciton mode contribute positively to the near-field enhancements, while "dark spots" provide negative contributions. The functionalized tip exhibits pronounced field gradient effects compared to the bare tip, significantly improving sensitivity and selectivity in near-field spectroscopy. Moreover, both the field enhancement and field gradient effects of the functionalized tip can be effectively tuned by adjusting the excitation energy and tilt angle. These results provide crucial insights into near-field modulation for molecules resonating with plasmonic nanocavities. The development of molecule-functionalized tips offers a promising pathway to advancing PES technology, enabling enhanced sensitivity and selectivity for molecular characterization.