Dielectric Properties of Shape-Distributed Ellipsoidal Particle Systems

The effective dielectric function of composites consisting of particles dispersed in isotropic or anisotropic media is affected by the composition, size, shape, and orientation of the particles. Our first objective was to determine the effects of the particle's shape and preferential orientation on the effective dielectric function of the medium. We have used the Maxwell Garnett effective medium approximation generalized for ellipsoidal particles in order to study the effective dielectric function of different Au nanoparticle systems, with both random and normal orientation of the ellipsoids in relation to the incident light, simulating the microstructure of many nanocomposite thin films grown by co-deposition or alternating deposition methods. Our second objective was to consider real particle systems by determining the effects of the particle shape distribution on the effective dielectric function. We have considered the Generalized Maxwell Garnett equations extended for systems of shape-distributed ellipsoids and have, for the first time, correlated the ellipsoid's shape/aspect ratio with their geometrical factors in a single graphic. We have introduced and used 1D and 2D Gaussian shape probability distribution functions in order to calculate the effective dielectric function of a number of Au nanoparticle systems having different distributions of ellipsoidal shapes/aspect ratios. The multicomponent Generalized Maxwell Garnett approximation was also used in order to determine the effective dielectric function of Au nanoparticle systems containing mixtures of nanoparticles with different shapes and sizes.