Vertically‐Aligned Ag Nanowire Array‐Based Metamaterial with High Refractive Index and Low‐Dispersion in the Infrared Band

Abstract To open new vistas for designing nanophotonic systems, exploiting high refractive index (RI) availability is now drawing attention worldwide, especially in the visible‐infrared range. Based upon the nanoscale close‐packed arrangement of metallic nano‐units, few optical‐frequency metamaterials with high RIs have been demonstrated. However, there are still significant challenges in their RI promotion, tuneability, and integrated preparation for practical applications. Herein, a novel Ag nanowire‐based metamaterial scheme is put forward, in which vertically aligned Ag nanowire (NW) array embedded‐Si or ‐Ge composites are made. Thanks to flexible control on microstructure parameters of Ag NWs (meta‐unit) and their dielectric environment, the synergistic effect of enhanced capacitive coupling and weakened diamagnetic response is created, leading to a recorded near‐infrared high‐RI of ≈7.2, low‐dispersion from 2 to 10 µm, and customizable RIs. Further, an air nanohole array‐Si composite layer, acting as an impedance matching layer, is utilized to realize the transmittance increase of the metamaterial film by ≈50% at specific wavelengths, along with the bulk plasmon‐polariton (BPP) modes resonances in the interwire nanocavities. This approach to increasing the infrared refractive index can circumvent physical effect conflict in high RI metamaterials and pave a basis for future scalable and on‐demand photonic applications.