Carbon-in-silica composite selective solar absorbers: a determination of composition and dielectic properties - SAIP Poster

Abstract

The Bruggeman and Maxwell-Garnett effective medium approximations (EMAs) have been used to investigate optical properties of composite materials. The EMA assumptions are based on random unit cell models in which metal particles are embedded in a dielectric medium. The embedded particles can be varied between spherical, ellipsoidal and cylindrical shapes. An interesting structure of connected short chains of amorphous carbon intermixed with silica chains at nanoscale level has been observed. The Bruggeman and Maxwell-Garnett EMAs could not model the optical properties of these materials; neither could the Bergman-Milton bounds approach. A generalised Bergman representation is applied on these carbon-in-silica samples with successful fitting between experiment and theory. The curve-fitting procedure resulted in information such as volume fraction of carbon relative to silica, percolation threshold and film thickness