Abstract
It is shown that the ellipsometric spectra of short range ordered planar arrays of gold nanodisks supported on glass substrates can be described by modeling the nanostructured arrays as uniaxial homogeneous layers with dielectric functions of the Lorentz type. However, appreciable deviations from experimental data are observed in calculated spectra of irradiance measurements. A qualitative and quantitative description of all measured spectra is obtained with a uniaxial effective medium dielectric function in which the nanodisks are modeled as oblate spheroids. Dynamic depolarization factors in the long-wavelength approximation and interaction with the substrate are considered. Similar results are obtained calculating the optical spectra using the island-film theory. Nevertheless, a small in-plane anisotropy and quadrupolar coupling effects reveal a very complex optical response of the nanostructured arrays.
Highlights
The optical properties of metallic nanoparticles have been of interest for many years and the scattering of electromagnetic waves by spheres and spheroids has been rigorously calculated before [1,2]
We have investigated the optical response of gold nanodisks arrays by spectroscopic ellipsometry and irradiance measurements at oblique and normal incidence
The effective optical response of gold-based nanostructured arrays produced by hole-mask colloidal lithography has been studied using two approaches
Summary
The optical properties of metallic nanoparticles have been of interest for many years and the scattering of electromagnetic waves by spheres and spheroids has been rigorously calculated before [1,2]. The simplest model to describe the optical properties of nanostructured arrays supported on a substrate is a homogeneous anisotropic layer In this case, the components of the dielectric function tensor can be modeled with Lorentz harmonic-type oscillators or anisotropic effective medium theories [24,25,26]. Higher-order multipole interactions were extensively investigated by Bedeaux and Vlieger leading to the formulation of the island-film theory [27] This theory is based on the notion of excess quantities and surface susceptibilities providing modified Fresnel coefficients that have successfully explained the optical response of small metallic nanoparticles on a surface [28,29,30,31].
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