Colloid precipitation electrodeposition

Generally, the experimental results on electrodeposition of CdS in acidic solutions of thiosulfate have implied that CdS growth does not involve underpotential deposition of the less noble element (Cd), as would be required by the theoretical treatments of compound semiconductor electrodeposition. Hence, a fundamental difference exists between CdS and the other two cadmium chalcogenides, CdSe and CdTe, for which the UPD model has been fairly successful. Besides, in the present case, colloidal sulfur is generated in the bulk of solution, giving rise to homogeneous precipitation of CdS in the vessel, so that it is quite difficult to obtain a film with an ordered structure. The same is true for the common chemical bath CdS deposition methods. 

The design of the interstices filling in colloidal crystals with appropriate media and subsequently fluid-solid transformation is central to the whole synthesis. Fluid precursors in the voids of crystal arrays can solidify by polymerization and sol-gel hydrolysis. More recently, many methods have been developed including salt precipitation and chemical conversion, chemical vapor deposition (CVD), spraying techniques (spray pyrolysis, ion spraying, and laser spraying), nanocrystal deposition and sintering, oxide and salt reduction, electrodeposition, and electroless deposition. 

Saitou et al. let the S colloids produced from the decomposition of S203 ions to completely precipitate and then used the top clear solution for electrodeposition. The authors indicated that no S existed in the solution and that S was produced from the following reaction [150] ... 

If the localized pH at the cathode surface becomes sufficiently high, cadmium can be precipitated and removed as colloidal Cd(OH)2. The direct electrodeposition of nickel is too slow to be significant, but it is precipitated as solid Ni(OH)2 at pH... 

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