Figure 3: Evolution of the single-molecule Fano spectra with different energy detunings.
(a) Experimental STML spectra (−2.5 V, 200 pA, 20 s) showing pristine nanocavity plasmon mode (blue lines, measured with the tip far away from the molecule) and the corresponding Fano resonance (red lines) for different detunings. The situation of zero detuning is marked with an arrow. (b) Simulated Fano spectra (red lines) for different detunings from −111 to 63 meV. The plasmonic background spectra (blue lines) are introduced by Lorentzian lineshapes with the peak position determined by the different detunings accordingly. (c) Variation of Fano parameter q as a function of detuning for different tip positions: r=0 (square), r=0.4 nm (circle), and r=0.8 nm (triangle). The purple, green and orange dashed lines are linear fits to the corresponding data. (d) Peak-maximum positions of the experimental Fano spectra as a function of the plasmonic frequency. Blue and red dots correspond to the upper- and lower-energy peaks (denoted as ωU and ωL), respectively. Two solid lines are theoretically fitted curves (Supplementary Note 6). The dashed lines represent the positions of the plasmonic frequency ωp and the molecular transition frequency ωm. The energy separation at zero detuning, Ωs, is marked in green.
