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

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 & AP;7.2, low-dispersion from 2 to 10 & mu;m, 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 & AP;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.

Automated summary

To explore new possibilities for designing nanophotonic systems, the use of high refractive index (RI) availability is gaining global attention, particularly in the visible-infrared range. Although some optical-frequency metamaterials with high RIs have been demonstrated, there are still challenges in promoting their RI, achieving tuneability, and integrating them for practical applications. This study presents a novel Ag nanowire-based metamaterial scheme, using vertically aligned Ag nanowire (NW) array embedded-Si or -Ge composites. By controlling the microstructure parameters of the Ag NWs (meta-unit) and their dielectric environment, a synergistic effect of enhanced capacitive coupling and weakened diamagnetic response is created, leading to a recorded near-infrared high RI of approximately 7.2, low-dispersion from 2 to 10 μm, and customizable RIs. Additionally, an air nanohole array-Si composite layer, acting as an impedance matching layer, is utilized to increase the transmittance of the metamaterial film by approximately 50% at specific wavelengths, along with the resonances of bulk plasmon-polariton (BPP) modes in the interwire nanocavities. This approach to increasing the infrared refractive index can overcome physical effect conflicts in high RI metamaterials and provide a foundation for scalable and on-demand photonic applications.