Radiative and non-radiative coupling between a molecule and a metallic tip

Abstract
We study numerically the radiative and non-radiative decay rates of a molecule close to the apex of a metallic tip as well as the local field enhancement factor. We show that the enhancement of the fluorescence strongly depends on the condition of illumination and is better when the dipole transition moment is vertical. We also investigate the influence of a small defect located close to the tip apex. We show that it may substantially modify the ratio between the radiative and the non-radiative contributions, and induce a frequency shift of the resonances. This may explain why experiments on single-molecule fluorescence dramatically depend on the tip quality.