Electroless copper deposition in the photographic gelatin layer

An electroless copper deposition process consisting of two stages: (1) forming gold catalytic centers, and (2) electroless copper deposition, was studied in this paper. The changes of the chemical state of sulfur in photographic gelatin before and after electroless copper deposition were studied by x-ray photoelectron spectrometry. The depth distribution of copper and gold within the electrically conductive layer produced by electroless copper deposition was determined and the mechanism of electroless copper deposition catalyzed by gold in the photographic gelatin layer was discussed. The results indicated that under acidic conditions (pH 3.20), methionine sulfoxide in the gelatin macromolecule had relatively high reducing power. When the gelatin sample was immersed into the chloroauric acid solution, methionine sulfoxide and methionine were oxidized to methionine sulfone, reducing Au exp 3+ to colloid gold which acted as the catalytic center at the initial stage of the electroless copper deposition. During the electroless deposition, the reduction of Cu exp 2+ by HCHO could continue, and even the copper completely covered the gold because the reaction was autocatalyzed by newly formed copper. Spectra., 15 ref.