The optical constants (n,k) of pure aluminum, silver, and aluminum/silver bilayer films with different thickness combinations (200 A total) were determined by the attenuated total reflection (ATR) method using the Kretschmann configuration. The simplex method was used for data fitting. The extinction coefficients k of pure aluminum and silver films are around 6 and 4 respectively, which are close to the bulk values.
The graph of k versus the thickness of the aluminum layer exhibits a minimum value of approximately 2 for the double-layer sample with 120 A of aluminum and 80 A silver. Whereas, the graph of the index of refraction n versus the thickness of the aluminum layer does not exhibit such behavior for the bilayer films.
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