OPTICAL-PROPERTIES OF A METAL ISLAND FILM CLOSE TO A SMOOTH METAL-SURFACE

Bright colors have been observed when a metal island film is deposited on top of a silver mirror with a separating quartz layer. For spacer layer thicknesses that are varied from 0 to 140 nm, the visual appearance changes from blue, black to a series of brilliant spectrumlike colors. The sequence is repeated similarly for higher interlayer thicknesses. The phenomenon is analyzed in terms of a stratified medium theory by using TEM data and an electromagnetic model for the optical constants of the metal island film. For island films with a sufficiently high absorbance (> 0.35), the spectra are characterized by two sharp minima where the reflectivity drops to values below 10(-3). The observed thickness dependence is analyzed in terms of a complex combination of the phase shifts caused by the island film, the spacer, and the relevant interfaces.