Immersion plating of metals (Ag, Cu, Ni) onto a porous silicon (PS) layer from aqueous and nonaqueous solutions has been studied. 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 microstructure of PS samples after the plating process. In both solutions, the deposition of metal oxidizes PS simultaneously to SiO2. The different deposition behaviors are discussed in terms of different rest potentials of PS in these solutions and electrode potential of each metal. Immersion plating in nonaqueous organic solutions shows that a trace of residual water affects the metal deposition. Based on the results obtained, the mechanism of metal deposition is proposed. The metal deposition proceeds by nucleation and growth via the local cell mechanism. It is also found that metal deposition proceeds very differently on Si wafer and PS surfaces. The different deposition behaviors on both surfaces are discussed. © 2002 The Electrochemical Society. All rights reserved.

A p-type semiconductor CuO film with a bandgap energy of 1.4 eV has been prepared by anodic electrodeposition in a basic aqueous solution containing copper nitrate hydrate and ammonium nitrate at 297 K, and the structural, optical, and electrical characterizations were carried out. The randomly-oriented CuO film prepared on a transparent conductive glass substrate showed electrical characteristics of a 1.26 × 103 Ω cm in resistivity, 2.11 × 1016 cm−3 in carrier concentration, and 0.234 cm2 V−1 s−1 in mobility, and a slight photocurrent generation could be observed during light irradiation. The (002)-oriented CuO film could be prepared on the (111)-oriented Au/Si wafer substrate and possessed an excellent photoactivity of a large photocurrent density and quick response compared to those for the randomly oriented CuO film.

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Immersion plating of nickel ͑Ni͒ on a porous silicon ͑PS͒ layer has been investigated in concentrated ammonium fluoride (NH 4 F) and dilute hydrofluoric acid ͑HF͒ solutions containing Ni 2ϩ . When the PS sample was exposed to the bath containing 5 M NH 4 F and 50 mM Ni 2ϩ at pH 8, metallic Ni was clearly observed at the open-circuit potential without using a reducing agent or any activation treatment at room temperature. However, no deposition was detected when the sample was immersed in a 0.5 wt % HF solution containing the same concentration of Ni 2ϩ at pH 2. The different deposition behavior is discussed on the basis of mixed potential theory, changes in the stability of Si-H bonds of PS as indicated in the Fourier transform infrared spectra, and the different state of Ni complex formation as obtained from the UV-vis spectra. The position of the Ni redox levels in both solutions with respect to the bandedges of Si was also determined and the results revealed a nearly similar energetic situation. Results from current-potential curves showed that a slow Ni deposition from the alkaline solution occurred in the dark and different possible reaction mechanisms were proposed. They also revealed the enhancement of the deposition under illumination, indicating that the deposition mechanism is electron transfer from the conduction band. X-ray photoelectron spectroscopy detected no silicon oxides on the PS surface after being immersed in the alkaline solution, giving merit that a binary PS/Ni nanostructure without Si oxides can be successfully achieved.

PACS 68.37.Hk, 81.07.Bc, 82.45.Vp Copper deposition into ordered macroporous silicon prepared in p-type substrates was investigated by immersion plating and electrochemical deposition in an aqueous solution containing Cu 2+ ions. When the sample was immersed in 0.1 M CuSO 4 solution at the open circuit potential, Cu crystallites are clearly observed at the top surface and inside the pores. The deposition of Cu oxidizes the substrate simultaneously to SiO 2 . On the other hand, the potentiostatic deposition in the dark revealed that Cu deposits preferentially at the pore bottom and propagates towards the top surface. Furthermore, when the substrate was illuminated under cathodic potential, the Cu deposition was enhanced mainly at the top-surface and around the pore walls. The different deposition behavior was compared and discussed.