Growth of polycrystalline nickel hydroxide films from aqueous solution. Solution chemistry, deposition methods, film morphology and texture

摘要

Deposition of functional ceramic films on different substrates by using soft aqueous solution processing can represent a cheap, low- energy and environmental friendly alternative to other film technologies. In this study β-Ni(OH)_2 polycrystalline films were grown on polytetrafluoroethylene, NiO, glass, copper, and Y:ZrO_2 substrates from Ni~(2+)-NH_4OH aqueous solutions. A careful control of solution supersaturation was essential to induce heterogeneous nucleation on the substrate and film growth. This was realized through the gradual decomposition of the nickel amino complexes Ni(NH_3)_n~(2+) using two different methods. Thermodynamic modeling of the Ni-NH_4OH-H_2O system was used to provide some general indications for defining the experimental conditions most suitable for film deposition and understanding the role of solution chemistry on film formation. Film microstructure and texture can be controlled by varying the substrate, the ammonia concentration, the ammonia evaporation rate, the soaking time and by adding a surfactant like sodium dodecylbenzensulphonate. As a result, films with different morphologies and orientations, as well as a uniform decoration of the substrate surface with Ni(OH)_2 crystals, were obtained. The proposed method can be extended to the preparation of oxide and hydroxide films of other transition metals forming moderately stable amino complexes.