Influence of surface effects in the determination of the optical constants of Cu–PbI_2 cermet films

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Abstract
The determination of optical constants of thin film Cu–PbI2 cermets using a photometric method has shown an unexpected variation of the results with respect to the thickness of the film. These effects are analyzed in detail in this paper. To understand the origin of this discrepancy an alternate method of determination of optical constants has been set up by using a new double-slit interferometer. This method, quite general and particularly well adapted for the study of absorbing films, allows the elimination of the surface effects and retains only the contribution from the volume optical constants of the films. Results from both methods are compared and they show that the surface effects are practically negligible for relatively thin films (d = 25 nm).