Mechanism of immersion deposition of Ni–P films on Si(100) in an aqueous alkaline solution containing sodium hypophosphite

The immersion deposition of Ni–P films on Si(100) surface without prior activation by metallic catalytic was carried out in an aqueous alkaline solution containing sodium hypophosphite. The deposition mechanism was investigated by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Two stages of deposition were observed when the Si substrate was immersed in the deposition solution at an appropriate pH value. In the first stage, crystalline Ni nanoparticles were formed through a galvanic displacement reaction, which accompanied the oxidation of Si substrate without involving the reducing agent, NaH2PO2. Experimental results indicate that the oxidation states of Si4+ and Si3+ exist in the oxide layer. The amount of suboxide, Si3+, increased with deposition time, and the oxide layer became activated. In the second stage, amorphous Ni–P was deposited on this activation oxide layer in a process involving the reducing agent. The microscopic structure of the deposition film, observed by TEM cross-sectional analysis, verifies the mechanism of deposition suggested in this study.