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Existence Conditions of High-k Modes in Finite Hyperbolic Metamaterials
摘要： The capability to support optical waves with very large wave vectors (high-k) is one of the principle features of hyperbolic metamaterials (HMMs). These waves play the key role in HMM applications such as imaging and lifetime engineering. E?ective medium approximation (EMA) as widely used analytical method to predict HMMs behavior, has shortcomings in calculating high-k modes of practical structures. EMA is applicable to a subwavelength unit cell of implicitly in?nite periodic structures. Using conventional EMA, in the present paper, boundary e?ects and spatial dispersion are taken into consideration to properly compute the high-k modes of ?nite-thickness multilayer HMMs. Applying nonlocal homogenization to stacks of alternating metal-dielectric layers, the corresponding e?ective medium is examined as a high-k waveguide sandwiched between the substrate and an ambient superstrate. The developed theory enables us to recognize two types of bulk waves coined as short-range and long-range propagating modes. Number of such modes as well as their cuto? conditions are quanti?ed for the ?rst time. Validity of the developed theory is veri?ed both numerically by rigorous simulations of the multilayer structures with the transfer matrix method and experimentally by optical characterization of the HMMs in infrared regime.
关键词： subwavelength metal-dielectric multilayers,e?ective medium theory,high-k modes,hyperbolic metamaterials
更新于2025-09-19 17:15:36
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Plasmonics of Diffused Silver Nanoparticles in Silver/Nitride Optical Thin Films
摘要： Metal-dielectric multilayers are versatile optical devices that can be designed to combine the visible transmittance of dielectrics with the electronic properties of metals for plasmonic and meta-material applications. However, their performances are limited by an interfacial optical absorption often attributed entirely to the metal surface roughness. Here, we show that during deposition of AlN/Ag/AlN and SiNx/Ag/SiNx multilayers, significant diffusion of Ag into the top dielectric layer form Ag nanoparticles which excite localized surface plasmon resonances that are primarily responsible for the interfacial optical absorption. Based on experimental depth profiles, we model the multilayer’s silver concentration profile as two complementary error functions: one for the diffused Ag nanoparticles and one for the interface roughness. We apply the Maxwell-Garnett and Bruggeman effective medium theories to determine that diffusion characteristics dominate the experimental absorption spectra. The newfound metal nanoparticle diffusion phenomenon effectively creates a hybrid structure characteristic of both metal-dielectric multilayer and metal-dielectric composite.
关键词： Plasmonics,Metal-dielectric multilayers,Optical thin films,Silver nanoparticles,Localized surface plasmon resonances
更新于2025-09-16 10:30:52