• J N Chazalviel

      Articles written in Journal of Chemical Sciences

    • On the corrosion of a promising photoelectrochemical material: The anodic dissolution ofp-Si in fluoride electrolytes

      M Etman J N Chazalviel F Ozanam

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      A study of cyclic voltammetry ofp-Si as a function of pH, fluoride ion concentration and electrode rotation rate was carried out. Thei/V characteristics exhibit similar general tendencies: a very rapid current increase (porous silicon generation), followed by a first sharp peak, a narrow polishing plateau, another broad maximum and finally a second plateau covering several volts. Using the rotating disc electrode, the kinetic and diffusional current contributions in the anodic dissolution ofp-Si in fluoride electrolytes are separated. The diffusion limitation seems to be due to the same species over the entire potential range studied.

      Impedance measurements at low frequencies confirm an inductive behaviour in the region of porous Si generation. In this regime, the series resistanceRsis 1–2 orders of magnitude higher than in other regimes. The presence of an interfacial silicon oxide layer in the region just beyond the first peak was evidenced through admittance results. The cyclic voltammograms show the appearance of current oscillations for voltages higher than ≅2·5 V. These oscillations are the finger-print of a characteristic resonance frequency of the interface,f0. In the same potential region, admittance measurements exhibit a resonance at the same characteristic frequency. Secondary resonances atf0 overtones were evidenced suggesting the existence of microscopic spontaneous oscillations of the oxide thickness.

    • In-situ infrared study of the interfacial layer during the anodic dissolution of a silicon electrode in a fluoride electrolyte

      F Ozanam C da Fonseca J N Chazalviel

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      The anodic dissolution ofp-Si in fluoride media has been studied, usingin-situ infrared spectroscopy, for various compositions of the electrolyte (fluoride concentration andpH). The interfacial layer present in the electropolishing regime has been investigated as a function of potential. At potentialsE<1–2VSCE, this layer mainly consists of a wet oxide or hydroxide. A well-defined oxide appears only aboveE∼2VSCE, beyond a second current maximum. The thickness of the oxide layer is in the range 0–100Å, and increases with increasing potential. The infrared spectra of the oxide layer reveal a minimum structural disorder of the oxide in the mid-region of the second current plateau. The potential range of this optimum oxide perfection increases when going to electrolytes giving rise to lower current densities. Incorporation of ions from the electrolyte may occur in the low-potential range. Potential-modulated infrared spectroscopy reveals a large accumulation of holes forE>2VSCE. This indicates that, in this potential range, the limiting step for anodic current flowing is the availability of sites for hole transfer into the oxide layer. On the other hand, the weak hole accumulation which is observed forE<2VSCE indicates a large density of hole-acceptor sites in the wet oxide layer. Finally, the current oscillations observed in the far anodic region (E>3VSCE) are found to be associated with an oscillation of the oxide thickness, which may reach an amplitude of the order of 30Å.

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