Optical properties of thin Au−Cr films and their application to solar energy conversion

Abstract

Opaque Au and Au−Cr films were produced by rf triode sputtering onto a glass substrate at 150°C. Cosputtering of Au and Cr films has extended the solubility limits of Cr in Au from 19 at.% Cr to 48 at.% Cr. Electron microscopy showed polycrystallinity in the entire solubility range and electron microprobe analysis confirmed compositional uniformity of films. Reflectance measurements were made in the range 0.3−15 μ. Reflectance data were analyzed by the Kramers−Kronig method to obtain the optical constants n, k, ε1, and ε2. Good agreement is shown with the previous single crystal data on Au−Cr (up to 19 at.% Cr). The reflectance data are used to calculate α/ε ratio which is applied to the solar energy collector surfaces. Reflectance and transmittance data for very thin Au and Au−Cr films (100−400 Å) are used to calculate the figures of merit for the heat mirror type solar−thermal energy collector design.