Effective Medium Properties of Arbitrary Nanoparticle Shapes in a Localized Surface Plasmon Resonance Sensing Layer

摘要

Inhomogeneous nanoparticle layers are often modeled as effective homogeneous layers in order to simplify optical device design. Maxwell—Garnett (MG) theory is often used to find the effective medium properties of localized surface plasmon resonance (LSPR) sensing layers. However, MG theory is only applicable for small spherical particles with low filling fractions, thus limiting its applicability. In this paper, an extraction method is used to determine the effective medium properties of an LSPR sensing layer consisting of metal nanoparticles of arbitrary shape. Complex reflection and transmission coefficients (5 parameters) are found using CST Microwave Studio (CST MWS), a commercial software package. Effective index of refraction (n_(eff)) and impedance (z_(eff)) are calculated from the simulated S parameters. This method is extended to account for substrate effects on the effective medium properties. Thus, this method allows for more accurate homogenization of LSPR sensor layers made of any nanoparticle shape, enabling improved LSPR device design.