Figure 3

Average local electric field enhancement on the SLG surface. (a) Calculated average electric field intensity enhancement on the SLG surface on top of the nanohole array substrate as a function of wavelength for air (black) and water (red) on top of the SLG. Average electric field intensity enhancement on the SLG surface on glass substrate is also shown (blue). E ₀ is the field amplitude of the excitation source. The resonance wavelength is shifted from 441 nm to 544 nm after addition of water on the SLG. At the 532 nm pump laser wavelength the plasmonic nanohole array substrate enhances the spatially averaged electric field intensity on the surface of the SLG at z = 0 by a factor of ~5. The intensity of electric field is enhanced ~20 times on the surface of the plasmonic nanohole array substrate when it is covered with water droplets compared to the surface of a glass substrate. (b) Electric field profile across the silver-dielectric interface calculated at point A (Fig. 3d) at the resonant wavelengths of the structure covered with air (441 nm) and water (544 nm). In the simulation setup the SLG is placed at z = 0. Field amplitudes are normalized with respect to the field amplitude at the SLG location when it is covered with air. (c) Electric field profile across the silver-dielectric interface calculated at point A at excitation wavelength of 532 nm. Standing waves above the silver layer are expected since the pump laser excitation wavelength is away from the resonance wavelength of the structure with SLG on the nanohole array and covered with air. (d) Normalized electric field intensity with respect to the intensity of the excitation field on the surface of the SLG when graphene is covered with air. (e) Same as (d) except that graphene is covered with water. The polarization of the excitation source is also shown.