Research ArticleOPTICS

Electrochemically controlled metasurfaces with high-contrast switching at visible frequencies

See allHide authors and affiliations

Science Advances  05 May 2021:
Vol. 7, no. 19, eabd9450
DOI: 10.1126/sciadv.abd9450
  • 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 tPANI, h2 = tPANI + 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.

  • Fig. 2 In situ optimization of the metasurface performance.

    (A) Schematic of the experimental setup. The metasurface on ITO (working electrode) is immersed into an electrolyte in a glass cell along with a Pt wire (counter electrode) and a Ag/AgCl reference electrode. Right-handed circularly polarized (RCP) light impinges on the sample at normal incidence, and the anomalous transmission intensity is recorded. (B) Cyclic voltammetry diagram for the electrochemical deposition of PANI on the metasurface sample. A potential range from −0.2 to 0.8 V and a scan speed of 25 mV/s are used. (C) SEM image of the metasurface with the optimized PANI thickness. Scale bar, 200 nm. (D) Atomic force microscopy image of the metasurface and selected height profiles. The measured thickness of PANI coated on the gold nanorods, tPANI, is approximately 50 nm (i.e., h2 = 100 nm). (E) In situ recorded normalized intensity of the anomalous transmission during the PANI growth (scheme A). The electrochemical process is halted when the intensity reaches the minimum (coating cycle 36, red circle). The intensity contrast defined as the ratio between the maximum and minimum intensities is as high as 860:1.

  • Fig. 3 Switching performance of the electrochemically controlled metasurface.

    (A) Intensity of the anomalous transmission in dependence on the applied voltage. (B) Switching times for the off→on and on→off processes. The rise time is approximately 48 ms (left) and the fall time is approximately 35 ms (right). (C) Highly reversible switching of the anomalous transmission. No substantial degradations are observed over 100 switching cycles. All intensities are normalized by the intensity maximum achieved at the optimal tPANI.

  • Fig. 4 Control experiment.

    (A) In situ recorded normalized intensity of the anomalous transmission during the PANI growth (scheme B). The electrochemical process is halted at a coating cycle number of 36 for a direct comparison with scheme A. Inset, schematic of scheme B, in which all the gold nanorods on the metasurface are conjugated with PANI. The dimensions of the gold nanorods are the same as those in scheme A. (B) Light intensity contrasts (ratio between the maximum and minimum intensities) in dependence on the coating cycle for schemes A (red) and B (black), respectively. (C) Fall time in dependence on the PANI thickness tPANI in scheme B. The fitted curve follows the relation, τ = 0.0048tPANI2 + 12.3. The metasurface switching in scheme B is substantially slowed down for thicker PANI coatings.

  • Fig. 5 Electrochemically controlled addressable metasurface holography.

    (A) SEM image of the device containing two addressable metasurfaces (M1 and M2) controlled by independent electrodes. M1 and M2 are designed to reconstruct holographic patterns L and R, respectively. The lateral distance between M1 and M2 is 30 μm. Scale bar, 50 μm. (B) Experimental results. Holographic patterns L and R are electrochemically switched on and off without cross-talk in an addressable manner. (C) Intensity profiles of the holographic pattern L along the dashed lines in (B) at the on and off states, respectively.

Supplementary Materials

  • Supplementary Materials

    Electrochemically controlled metasurfaces with high-contrast switching at visible frequencies

    Robin Kaissner, Jianxiong Li, Wenzheng Lu, Xin Li, Frank Neubrech, Jianfang Wang, Na Liu

    Download Supplement

    This PDF file includes:

    • Supplementary Text
    • Figs. S1 to S7
    • Table S1
    • References

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article