Fano description of single-hydrocarbon fluorescence excited by a scanning tunneling microscope

TL;DR

This paper demonstrates submolecular resolution fluorescence detection of single hydrocarbons using a scanning tunneling microscope, revealing vibrational spectra and Fano interference effects in molecule-surface interactions.

Contribution

It introduces a novel Fano profile analysis of single-molecule fluorescence excited by tunneling electrons, expanding understanding of molecular luminescence mechanisms.

Findings

Vibrational progression in fluorescence spectra of hydrocarbons.

Distance-dependent Fano profiles indicating interplay of electrons, excitons, and plasmons.

Detection of molecular signatures even when tunneling current is spatially separated.

Abstract

The detection of fluorescence with submolecular resolution enables the exploration of spatially varying photon yields and vibronic properties at the single-molecule level. By placing individual polycyclic aromatic hydrocarbon molecules into the plasmon cavity formed by the tip of a scanning tunneling microscope and a NaCl-covered Ag(111) surface, molecular light emission spectra are obtained that unravel vibrational progression. In addition, light spectra unveil a signature of the molecule even when the tunneling current is injected well separated from the molecular emitter. This signature exhibits a distance-dependent Fano profile that reflects the subtle interplay between inelastic tunneling electrons, the molecular exciton and localized plasmons in at-distance as well as on-molecule fluorescence. The presented findings open the path to luminescence of a different class of molecules than investigated before and contribute to the understanding of single-molecule luminescence at surfaces in a unified picture.