Fig. 9

a Schematic design of the asymmetric heptamer with a₁ = 40 nm, a₂ = 60 nm, a₃ = 80 nm, d₁ = 5 nm, d₂ = 20 nm, d₃ = 15 nm, d₄ = 10 nm, d₅ = 25 nm d₆ = 6 nm, d₇ = 12 nm and h = 40 nm. The black arrow on the top presents the polarization of the excitation and the black dotted line at the middle of the heptamer shows the symmetry line; b Simulated scattering profile of the asymmetric heptamer. The magenta and red dotted (vertical) lines indicate the spectral position of the Fano dips at 835 nm and at 1160 nm, respectively; c and d NFE maps computed at a plane 1 nm above the top surface of the asymmetric heptamer at the Fano dips