The effect of MIM metasurface configuration on resonant mode localization is revealed by FDTD derived cross-sectional view plots in Figure . It is evident that, until SiO 2 spacer thickness is at or below = 30 nm, the majority of the optical field is tightly confined inside the insulator layer. However, as thicknesses become larger, the localization in the insulator layer is diminished, and modes start to exhibit a more pronounced dipolar character, typical for isolated nanodisk plasmonic structures. A majority of the optical field portion localized in the insulator layer is bound to eventually be converted to thermal energy in the free-carrier plasma of metals in the MIM structure. However, the portion loosely confined around a nanodisc particle is liable to re-radiated into free space, and should be considered as scattered. Hence, for our = 400 nm disc diameter metasurfaces, = 30 nm insulator thickness defines a delimiting line between the absorption dominated mode ( ≤ 30 nm) and primarily scattering mode for ≥30 nm.