Fig. 1. Working principle of the electrochemically controlled metasurface.

(A) Chemical structures of PANI at the ES and LS controlled by the applied voltage. (B) Schematic of the electrochemically controlled metasurface. Two sets of gold nanorods (200 nm by 80 nm by 50 nm) are arranged in alternating rows on top of an ITO-coated quartz substrate. One set is entirely covered by PMMA (height h₁), whereas the gold nanorods in the other set are locally conjugated with PANI (thickness t_PANI, h₂ = t_PANI + 50 nm). The complex refractive indices of PMMA and PANI are n₁ + ik₁ and n₂ + ik₂, respectively. (C) Normalized intensity of the anomalous transmission in dependence on the nanorod angle difference Δθ simulated at an operating wavelength of 633 nm. Here, n₁ = n₂ = 1.5, k₁ = k₂ = 0, and h₁ = h₂ = 100 nm. (D) Simulated anomalous transmission as a function of n₂ and k₂, when n₁ = 1.5, k₁ = 0, and Δθ = π/2. The black squares indicate the complex refractive indices (n₂, k₂) of PANI at different applied voltages.