Influence of thiourea on electroless Ni–P films deposited on silicon substrates

Electroless nickel–phosphorus films were produced on silicon substrates in alkaline bath solutions, with the addition of thiourea in a concentration range of 1.0–5.0 mg L−1. The influence of thiourea on the chemical composition, morphology and corrosion resistance of the films was studied. The results revealed thiourea had a major influence on plating rate, phosphorus-content and aggregate size. The optimal content of thiourea was 1 mg L−1. Thiourea accelerated the deposition rate at low concentration of 1 mg L−1, but deceased the deposition rate and the phosphorus content at high concentration. The surface of the film without thiourea was smooth and dense. Also, with increasing thiourea content, the surface evolved into coarse nodular morphology with clear intercolonial boundaries. With the addition of 1 mg L−1 thiourea, the film had better corrosion resistance compared to film without thiourea.