Influence of the shape and orientation of nanoparticles on the spectral characteristics of composite media with gold inclusions

Subject of study. The absorption and transmission spectral characteristics of composite media containing ellipsoidal gold nanoparticles, with various ratios of the axes of a spheroidal ellipsoid, are studied. Aim of study. The aim is to establish the mechanism by which the particle shape, angle of incidence of radiation, and polarization of optical waves influence the reflection and transmission coefficients of composite media with gold nanoparticles. Method. The Maxwell Garnett effective medium model was used. Main results. Based on a modification of the Maxwell Garnett model that accounted for the depolarization factor, an algorithm for calculating the spectral characteristics of the composite medium was developed. The spectral dependencies of the refractive index and extinction coefficient of the composite medium consisting of polystyrene and ellipsoidal gold nanoparticles were calculated. The results show that the orientation of the ellipsoidal particles in the composite medium plays a significant role. The amplitude of the extinction-coefficient peak depends on the shape of the particles introduced into the dielectric matrix. The transmittance spectral characteristics reveal the occurrence of plasmon-resonance absorption, which depends on the shape and orientation of the particles in the composite medium. The plasmon-resonance peak shifts from 518 nm to 640 nm as the nanoparticle shape changes. Practical significance. The results enable the prediction of the optical properties of composite media containing nanoparticles of various shapes, which is important for selecting materials with specified properties according to their intended application.