Immersion plating of nickel onto a porous silicon layer from fluoride solutions

The deposition of nickel (Ni) onto a porous silicon (PS) layer by immersion plating from acidic and alkaline fluoride solutions has been studied. In an immersion plating bath of simple hydrofluoric acid (HF) of pH 2 containing Ni ions, no metal deposition was observed. However, visible metallic Ni was deposited from the ammonium fluoride (NH₄F) alkaline solution of pH 8. The different deposition behaviors are discussed on the basis of mixed potential theory, etching rate of PS and the state of Ni complex formation. The modified PS layers after the immersion plating were analyzed by X-ray diffraction and X-ray photoelectron spectroscopy. Fourier transform infrared spectroscopy and scanning electron microscopy were also performed to investigate the structural changes and characterizations of PS samples after the plating process. A binary PS/Ni nanostructure without Si oxides is successfully achieved from the alkaline bath.