(a) Schematic diagram (not according to scale) of the unit cell for a structure consisting of the graded index dielectric slab shown in Figure 2b, with three columns of rhodium rods embedded in it. Each rod has radius r = 14 nm, and the rods are separated horizontally by  a_x  = 600 nm and vertically by a_y  = 250 nm. (b–d) Numerically calculated R, T, and A spectra for TM normal incidence on the structure shown in (a), with metal rods consisting of: rhodium of radius 14 nm in (b), tungsten of radius 8 nm in (c), and TiN of radius 24 nm in (d).