Fig. 4.

Time-resolved photoluminescence and Raman scattering spectra. a PL decay traces for a WSe${}_2$ monolayer placed on a planar GaP substrate (purple) and coupled to a nano-antenna with $r=200$ nm (yellow). Grey shows the instrument response function (IRF). The PL signal is measured with a 90-ps pulsed laser, under low excitation power of 0.2 W/cm${}^2$, to avoid exciton–exciton annihilation processes. Resolution-limited dynamics are measured for WSe${}_2$ coupled to a dimer. Dotted black lines show results of the fitting with exponential decay. b Raman scattering spectra for 1L-WSe${}_2$ placed on GaP nano-antennas with r = 50 nm (red) and 200 nm (yellow) and on the planar GaP (black). c Raman scattering spectra for 2L-WSe${}_2$ on a $r$ = 200 nm GaP nano-antenna (orange) and on the planar GaP (black). d Experimental Raman enhancement factor, ${⟨\mathrm{EF}⟩}^{\mathrm{Raman}}$ (see Eq. (3) in ‘Methods’), obtained (after background subtraction) for the 250 cm${}^{-1}$ peak in 1L- and 2L-WSe${}_2$ coupled to nano-antennas with various $r$