Fig. 1. Schematic illustration of TES configuration using the Ag tip and a substrate with monolayer MoS2 on the surface.

Fig. 2. Calculated electric field enhancement in TES configuration. (a) Comparisons of electric field enhancement (|M|2) of TES configuration with (D=2  nm) and without (D=1, 2 nm) monolayer MoS2. (b) Dependence of the electric field enhancement on the tip–MoS2-film distance, plotted as a function of wavelength. (c)–(f) Side views and (g) top view of the normalized electric field enhancement distributions with different tip–MoS2-film distance under 660 nm laser excitation.

Fig. 3. Calculated emission enhancement and fluorescence EF of monolayer MoS2 in TES configuration. Tip–MoS2-film-distance-dependent (a) quantum yield, (b) radiative decay rate enhancement, (c) nonradiative decay rate enhancement, and (d) fluorescence EF of monolayer MoS2 in TES configuration, plotted as a function of wavelength. Stokes shift was not considered for all data. The value for d=0  nm in (d) was multiplied by 1000.

Fig. 4. Calculated fluorescence EF under the assumption that Stokes shift between the emission and excitation wavelength was considered. Tip–MoS2-film-distance-dependent fluorescence EF of monolayer MoS2 at excitation wavelength of (a) 630 and (b) 660 nm. (c) Fluorescence EF of MoS2 at emission wavelength of 680 nm, plotted as a function of tip–MoS2-film distance. (d) Tip–MoS2-film-distance-dependent fluorescence EF of MoS2, plotted as a function of excitation wavelength (the emission wavelength was set at 680 nm). Stokes shift was considered for all data. The value for d=0 and 4 nm in (d) were multiplied by 100 and 10, respectively. Insets in (a) and (b) show the fluorescence EF of MoS2 with d=0 and 4 nm.