Thin Gold Films

Thin films of gold are readily produced on almost any solid substrate by techniques as diverse as electroplating, electroless deposition, and physical vapor deposition. These provide a means by which the desirable optical or surface properties of Au can be exploited without incurring excessive raw material costs. Due to the nobility of gold, such films will generally remain unoxidized, and can be prepared down to a thickness of a few tens of nanometers.

Films of less than 80 nm or so in thickness will transmit an appreciable fraction of any blue to green light that falls on them, with red light and the near-infrared being selectively blocked. This is due to the position of the band edge at about 2.4 eV, described previously. This property has stimulated the use of gold films in spectrally selective applications. The optical properties of Au thin films can also be significantly varied by control of the deposition conditions. The properties are not only controlled by film thickness, but also by the morphology of the film. In particular, the degree of percolation, or its absence, has a strong effect on the shape of the transmitted and reflected spectra [58,59]. Optimum reflectivity in the infrared requires a continuous coating.