Selective nature of gold-black deposits

Gold blacks made by evaporation from tungsten filaments in the presence of oxygen and in the absence of oxygen show different optical and electrical properties. The properties are found as a function of mass thickness for many different evaporation conditions. Electron microscopy was used to reveal the role of tungsten oxide in the deposit in breaking up the conducting paths and leading to selective optical behavior. Mie’s theory may be used to calculate the optical properties of a gold sol and, at least for the blacks with the smallest conducting regions, agreement with experiment is good. The application of metal sols to the production of selective surfaces is discussed.