Abstract
Heterogeneous nanostructures containing nanoparticles of various sizes and shapes have attracted significant attention in the development of nano-biosensors. Especially, plasmonic properties of such materials are advantageously exploited for the detection of biological and chemical substances. Since these media exhibit optical anisotropy, a valid homogenization procedure must be able to describe appropriately the relationship between the geometry of the inclusions and the nature of local field modes. We present a model approach for extension of the effective medium approximation (EMA) and its application to anisotropic nanostructures. The proposed model is based on a “strong-couple-dipole” (SCD) method including a volume-integral correction term in a Green tensor that enables to obtain more accurate representation of polarizability tensor. Derived depolarization factors for discs and bi-cone particles are compared with the early known shapes (spheroids, cylinders) and applied to nanostructures composed of the Fe or Au nanodots in polyacrylate.
Highlights
The development of novel nano-fabrication technologies has attracted significant attention because of the plasmonic properties of nanomaterials and the feasibility of exploiting them for the detection of biological and chemical substances [1]. Noble metal nanoparticles, such as gold and silver, exhibit unique optical resonance properties, and they have been proven to be useful for these applications [2,3,4]
The applicability of effective medium approximation (EMA) is restricted by the size of the structures composing the mixture; sufficiently large to preserve locally their own electromagnetic behavior and small enough for the composite to appear homogeneous compared to the wavelength of the interacting radiation
As the size and/or number of particle shapes should be explicitly incorporated within homogenization procedures, the deriving of corresponding depolarization tensors demands generalized methods, based, for example, on the Green electromagnetic tensor application [7,12]
Summary
The development of novel nano-fabrication technologies has attracted significant attention because of the plasmonic properties of nanomaterials and the feasibility of exploiting them for the detection of biological and chemical substances [1] Noble metal nanoparticles, such as gold and silver, exhibit unique optical resonance properties, and they have been proven to be useful for these applications [2,3,4]. The article is organized as follows: The Maxwell-Garnett model of EMA and the basic principle of SCD (strong-couple-dipole) polarizability model are introduced in their generalized forms for homogeneous anisotropic nanoparticles. This theory is presented with an extension for disc- and cone-shaped inclusions because depolarization factors for nanoparticles of these shapes have not been referred to so far in detail. The importance of correction factors is discussed
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