Unravelling the optical responses of nanoplasmonic mirror-on-mirror metamaterials

Abstract

Mirror-on-mirror platforms based on arrays of metallic nanoparticles, arranged top-down or self-assembled on a thin metallic film, have interesting optical properties. Interaction of localized surface-plasmons in nanoparticles with propagating surface-plasmons in the film underpins the exotic features of such platforms. Here, we present a comprehensive theoretical framework which emulates such a system using a five-layer-stack model and calculate its reflectance, transmittance, and absorbance spectra. The theory rests on dipolar quasi-static approximations incorporating image-forces and effective medium theory. Systematically tested against full-wave simulations, this simple approach proves to be adequate within its obvious applicability limits. It is used to study optical signals as a function of nanoparticle dimensions, interparticle separation, metal film thickness, the gap between the film and nanoparticles, and incident light characteristics. Several peculiar features are found, e.g., quenching of reflectivity in certain frequency domains or shift of the reflectivity spectra. Schemes are proposed to tailor those as functions of the mentioned parameters. Calculating the system's optical responses in seconds, as compared to much longer running simulations, this theory helps to momentarily unravel the role of each system parameter in light reflection, transmission, and absorption, facilitating thereby the design and optimisation of novel mirror-on-mirror systems.

Electrochemical plasmonic metamaterials: towards fast electro-tuneable reflecting nanoshutters

“…1c where light incident at an angleθ propagates with wavevector k in layer 1 (of relative permittivity 1 ε In what follows, we accurately model the known optical properties of gold and ITO by extending Drude (D) permittivity model to a Drude-Lorentz (DL) one, which is given as 11 : Figure 2 compares the real and imaginary parts of the permittivities of gold and ITO with the experimental data reported in the literature 15 . This shows how closely DL model can reproduce the experimentally measured values of permittivity of both gold and ITO over the range of optical wavelengths (λ) of interest.…”

“…This shows how closely DL model can reproduce the experimentally measured values of permittivity of both gold and ITO over the range of optical wavelengths (λ) of interest. For the system under study, we estimate the optical response from a layer of subwavelength NPs using our quasi-static effective medium theory 10,11 . First we describe the quasi-static polarizability of a cuboid of dimensions L x x L y x L z (for incident light polarized along one of its three axes) as 16…”

“…11 . The derivation of these equations using transfer matrix formulation and Fresnel coefficients across all interfaces are described systematically in Ref 11 .…”

“…We will start with the description of the putative system that could exist in two states. Then we present the results of the calculation of the optical response of such system, based on our original theory 11 , developed here subject to this case, and verified against full-wave computer simulations. The theory and simulations are in amazing agreement with each other, which gives us confidence that our model adequately describes the optical properties of the system.…”

“…This term refers to plasmonic metasystems based on electrode/electrolyte interfaces, solid-liquid or liquid-liquid 1 , which involve adsorption-desorption of plasmonic nanoparticles from the solution to the interface, tuned by variation of electrode potential and controlled by electrolyte concentration and pH of the solution. It has been predicted theoretically and shown experimentally, that rearrangements of such nanoparticles -from dispersion in the bulk to formation of arrays at the interface, may dramatically change optical properties of the interface 10 , be it mirror-window switching 2 , tuneable colour mirrors 11 , or SERS sensors 12 . One can read more about the progress in this area in recent review articles 1 .…”