Alternating Nanolayers of Dielectric MgF₂ and Metallic Ag as Hyperbolic Metamaterials: Probing Surface States and Optical Topological Phase Transition and Implications for Sensing Applications

Abstract

Hyperbolic metamaterials (HMMs) possess marvelous electromagnetic properties, which enable a wide variety of applications, such as super-resolution and spontaneous emission. In addition, HMMs have emerged as a plasmonic biosensor platform with extreme sensitivity owing to the higher quality factors of their surface states. When predicting and analyzing these optical properties of HMMs, most of the researchers adopted the effective medium theory (EMT). However, this theory only validated for the long wavelength limit and the infinite stacking layers. To demonstrate the optical topological transition, we fabricated planar one-dimensional HMMs (1D-HMMs) that are composed of alternating MgF 2 /Ag nanolayers with various filling ratios and mapped the dispersion of their surface states. Strikingly, all our analytic analyses, numerical calculations, and experimental measurements indicated that the "transition point" on the dispersion curve of the surface states of 1D-HMMs did not depend on the intrinsic metal/dielectric properties but depend only on the thickness ratio of the metal nanolayers to the dielectric nanolayers. This outperformed the conventional effective medium theory. The results based on our plasmonic band theory provided a more rigorous interpretation and will benefit the sensing applications of the 1D-HMMs.

Near-UV-to-Near-IR Hyperbolic Photonic Dispersion in Epitaxial (Hf,Zr)N/ScN Metal/Dielectric Superlattices

“…Though the optical losses are higher in TMN-based HMMs compared to the noble metal-based HMMs, their high-temperature stability, corrosion-resistant high hardness, and structural/morphological stability in the thin-film form make them attractive for practical applications. In addition, the wide-spectral coverage of these materials will not only be useful for the solid-state energy conversion fields such as solar–thermal, and solar–fuel, they will also be attractive for biophotonics, sensing, and illumination nanoscopy …”

Designing Metasurfaces for Efficient Solar Energy Conversion

“…Finally, the high Q -factor of the SLR may not be desired if the main target of the metasurface is efficient light harvesting across the entire solar spectrum. Therefore, metasurfaces exhibiting broadband optical absorption can be realized for instance by using metal/insulator/metal (MIM) structures. ,, This is further enhanced by employing a dissipative plasmonic material (high ε 2 (ω)) for the topmost layer, including TMNs (such as TiN) or other refractory metals (such as W, Ta, Mo), which also improves the performance under high temperature and harsh environmental conditions (Figure g) critical for solar-thermal applications such as TPVs. , …”

“…Therefore, metasurfaces exhibiting broadband optical absorption can be realized for instance by using metal/insulator/metal (MIM) structures. 15,98,99 This is further enhanced by employing a dissipative plasmonic material (high ε 2 (ω)) for the topmost layer, including TMNs (such as TiN) or other refractory metals (such as W, Ta, Mo), which also improves the performance under high temperature and harsh environmental conditions (Figure 3g) critical for solar-thermal applications such as TPVs. 100,101 Dielectric metasurfaces are usually made of high refractive index semiconductors, such as Si, Ge, and TiO 2 .…”