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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.

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Copper and nickel electrodeposition into ordered macropores prepared in p-type silicon has been studied in aqueous solutions containing cupric and nickel ions, respectively. When a macroporous silicon template was cathodically polarized in 0.1 M cupric sulfate solution, copper was deposited preferentially at the pore bottom in the dark, whereas the deposition was found to proceed not only at the pore bottom but also partially on the pore wall under the back side illumination. In contrast, the deposition of nickel in 0.1 M nickel sulfate solution was not possible in the dark, while deposition occurred uniformly on the entire surface of the pore wall under the back side illumination. Dissolution of silicon templates by the alkaline etching process led to the formation of copper microrods and nickel microtubes. The deposition behavior of both metals was compared and this discrepancy was discussed.

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Room temperature synthesis of porous SiO 2 thin films by plasma enhanced chemical vapor depositionPorous silicon rugate filters are fabricated and investigated for their ability to sense chemical species. The durability of the filter is tested by allowing the structure to undergo many cycles of adsorption and desorption of vapor-phase ethanol molecules. The characteristic reflectivity peak of the structure exhibits a relative blueshift of 2.7% after 86 adsorption/desorption cycles. The observed shift is ascribed to the formation of silicon dioxide, which has a lower refractive index than that of silicon. In order to stabilize the structure against oxidation expected from cycling and environmental exposure, the filter is subjected to electrochemical oxidation in an aqueous sulfuric acid electrolyte. The treatment dramatically improves stability of the sensor; a relative blueshift of Ͻ0.4% is observed after 100 adsorption/desorption cycles for this sensor. The sensitivity of the sensor is also affected by electrochemical oxidation: the response to saturated ethanol in air changes from ⌬ = 100 nm to ⌬ = 70 nm, respectively. Theoretical calculations using the Bruggeman effective medium approximation and the characteristic matrix method indicate that up to 15% ͑by volume͒ of silicon is transformed to silicon dioxide by the electrochemical oxidation procedure. This volume ratio is close to that estimated from Auger electron spectroscopy measurements.