Plasmon-enhanced photoluminescence spectroscopy of a single molecule in the subnanometer cavity

Abstract

We investigate the influence of quantum tunneling on the plasmon-enhanced electric field and photoluminescence spectroscopy in the subnanometer nanogap between two adjacent Ag nanoparticles using the quantum-corrected method. We analyze the contribution of nonlocal dielectric response at different separation distances to plasmon-enhanced fluorescence using the D-parameters method. Our results demonstrate the high sensitivity of the quantum-induced effect and nonlocal dielectric response to the separation distance. In cases of shorter separation distances, the localized fields start to decrease due to tunneling current short circuit, resulting in a substantial reduction in Raman enhancement. Additionally, the lower quantum yield caused by loss of electron-hole pairs further quenches the fluorescence intensity in the narrowing gaps. We achieve calculated Raman and fluorescence enhancement factors of 13 and 6 orders of magnitude. Under excitation wavelengths of 660 nm, we achieve spatial resolutions of 1.5 nm and 2.2 nm for Raman and fluorescence spectroscopy.