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60 nm is deposited on the MoS2 monolayers. The coupling strength between a single Au plasmon and MoS2 exciton can be e?ectively tuned by the gate voltage. (b) PL spectrum of the MoS2 monolayers on the SiO2/Si substrate, which shows a strong emission peak at ?680 nm. Inset: Corresponding Raman spectrum of the MoS2 monolayers. (c) Scattering spectra of the Au nanodisk with and without the MoS2 monolayers, and the absorption spectrum of the MoS2 monolayers (green line). The black dashed line represents the exciton?plasmon coupling region at ?660 nm. (d) The coupled oscillator model, which includes the LSP, neutral exciton, and trion as three oscillators. ACS Nano Article DOI: 10.1021/acsnano.7b05479 ACS Nano 2017, 11, 9720?9727

9721 A series of single Au nanodisks with di?erent radii were fabricated to systematically investigate the exciton?plasmon interaction of this Au?MoS2 hybrid nanostructure, and the generated Fano resonance based on a single nanodisk was measured by using a commercial hyperspectral dark-?eld imaging system (HIS V3, CytoViva Co.) (see Figure S3a?c). The coupling e?ciency of a single-nanoparticle modulator is mainly determined by the scattering cross section in Au/MoS2 hybrids (see Figure S3d?f). To achieve the best coupling of Figure 2. (a, b) Re?ection spectra of MoS2 monolayers with the gate voltage changed from +8 V to ?8 V. An obvious and continuous spectral tuning was found under either positive (a) or negative gate voltages (b). (c, d) Scattering spectra of a single Au nanodisk on the MoS2 monolayers with positive and negative gate voltages. As shown in (c), by increasing positive voltage from

0 V to

8 V, the Fano resonance is gradually weakened and ?nally turned o?. Conversely, an enhanced Fano resonance is turned on by increasing negative voltage as shown in (d). Figure 3. (a) Experimentally measured MoS2 A exciton intensity in the energy range of 1.78 to 1.9 eV for the gate voltage changed from ?8 V to +8 V. Neutral exciton (green line) and trion (orange line) that contribute to the A exciton (yellow line) are ?tted in the Lorentzian shape.44 The solid arrows represent the trend of the energy evolution of the neutral exciton and trion, respectively. (b) Measured (solid line) and calculated (dashed line) scattering spectra of the Fano resonance in the range of 1.78 to 1.95 eV under the same gate voltage as (a). (c) Calculated MoS2 A exciton intensity and its corresponding neutral exciton and trion contributions. ACS Nano Article DOI: 10.1021/acsnano.7b05479 ACS Nano 2017, 11, 9720?9727

9722 incident photon, the size of the Au nanodisk needs to be carefully tailored. The Au nanodisk with a radius of

60 nm was selected for the following experiment, because its plasmon resonance overlaps with the MoS2 A exciton in the frequency domain and thus can be used for the strong plasmon?exciton coupling, which is also con?rmed by the ?nite-di?erence time-domain (FDTD) simulations (see Figure S3d?f). To investigate the gate dependence of this Fano resonance, re?ection spectra of the pristine MoS2 monolayers at di?erent gate voltages (Vg) were ?rst tested as shown in Figure 2a and b, respectively, where the characteristic A exciton peak is found at ?668 nm when Vg =

0 V. With the Vg changed from

0 V to +8 V, the absorption intensity of the A exciton decreas........