The Resonance Type Absorption of Very Thin Silver and Gold Films

The spectral transmission from 200 mµ to 1,200 mµ of silver and gold thin films was measured. It was found that for heated silver films a strong resonance type absorption appeared with the peak at 435 mµ ∼ 480 mµ and then the absorption due to electrons in the conduction band disappeared. For heated gold films, the similar results were also obtained but the absorption strength was rather weak and the peak position shifted to 510 mµ ∼ 550 mµ. By taking into account the two dimensional aggregations, some discussions were made from the view point of the collective motion of conduction electrons within small metallic particles of which the film was composed.