Structural composition and optical properties of solar blacks: gold black.

Specimens of gold black (a test solar black system) were produced under controlled laboratory conditions so as to study the dependence of their optical properties on the particlelike nature of the material. A theoretical model incorporating the particulate nature of the gold black films has been applied to describe their optical properties. The electron collision frequency calculated within the framework of the model is significantly larger than that predicted from the particle size effects, and the interband contribution to the absorption coefficient is noticeably smaller for the small (40-85 A) gold particles than for bulk gold. The dependence of the absorption coefficient on particle size has also been determined.