Application of effective medium theory with consideration of island shapes to interpret optical properties of discontinuous Pt films.

Pt films with mass thicknesses ranging from 0.6 to 3.9 nm were evaporated onto quartz-glass substrates under vacuum conditions (p ~ 10(-4) Pa) with evaporation rate 0.01 to 0.2 mm/s. The transmittance spectra were measured in the wavelength range from 220 to 2500 nm. The microstructures were examined by a transmission electron microscope. The statistical distributions of island areas and the histograms of the fixed ratios of the semiaxes for ellipsoids were determined. It has been found that the transmittance spectra for the films with coverage coefficient 0.2≤p≤0.6 exhibit minima that shift with an increase in the coverage coefficient. To interpret the transmittance spectra of the films, the Maxwell-Garnett theory, which takes into account the island shapes, was used. Measured and calculated spectra were compared. For low coverage coefficients there is a quantitative agreement between the experimental and the calculated results.