Fig. 3
3-D maps of surface charge distributions with experimental and calculated absorbance spectra. a Surface charge distributions (arbitrary units) for the 8 nm Al2O3 sample at the indicated wavelengths corresponding to the multipolar mode (M), the gold interband transition (IB), the quadrupolar mode (Quad), and the gap plasmon mode (Gap) calculated with COMSOL assuming normally incident light polarized along the x-direction. Steady-state absorbance is simulated for samples with an 8 nm (b) or 25 nm (c) Al2O3 spacer assuming a nanocube density of 4 μm−2 and compared to the experimental ensemble response of the metasurface. The calculated absorbance is also broken down into the relative contributions to absorbance from the Ag and Au components. The inset to b is a comparison of three experimental absorbance spectra of single nanocubes (NCs) at the gap mode to the simulated spectrum, showing an excellent agreement between homogeneous linewidths
