A Study of the Mechanism of Copper Physical Development

The shapes of silver image and copper image formed by copper physical development were studied by electron micrography, and the composition and the chemical state of the final image were studied by X-ray photoelectron spectrometry in this paper. It was indicated that silver filaments of the original image were transformed to branched silver halide by the activation process and new silver deposited in branched form first during the copper physical development, the newly formed silver contains two chemical states: monoatomic and polyatomic state. The silver at the image surface is exclusively in the monoatomic state. The presence of polyatomic state causes the shift of the binding energy of Ag3d to a low value. The stress in the crystal lattice caused by the deposition of copper forces silver atoms to diffuse to the image surface. Both newly formed silver and copper are catalytic. However, with increase of the time of copper physical development the amount of copper on the surface increases and silver is at last completely covered by copper. From then on the copper physical development continues because of the autocatalysis of copper.