Fig. 2

Absorption spectrum varies with the gap sizes between adjacent tips of triangles increasing of MIM structure array (a) and MII structure array (b). The inset at the top-right corner of a is absorption spectrum of isolated MIM structure. c–e Electric field |E| distribution of xoz plane (y = 0 nm) of MIM structure array models with gap sizes of 20 nm, 30 nm, 50 nm, respectively. f |E| distribution of xoz plane (y = 0 nm) of MII structure array model with gap size 30 nm. g |H| distribution of xoz plane (y = 0 nm) of MIM structure array model with gap size of 30 nm. h |E| distribution of xoy plane (z = − 30 nm) of MIM structure array model with gap size of 30 nm