Resonant and Nonresonant Behavior of the Anodic Dissolution of Silicon in Fluoride Media: An Impedance Study

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Abstract
The anodic dissolution of silicon in fluoride media has been investigated by impedance measurements. In nonresonant conditions, behavior typical of metal corrosion is observed: at low positive potentials, up to a first current maximum (regime of porous silicon generation), the main feature of the impedance is an inductive component, accounted for in terms of roughening of the surface; at more positive potentials, corresponding to a first current plateau (electropolishing regime), the main contributions to the impedance arise from the oxide layer formed onto the silicon surface. At potentials beyond a second current maximum, a steady‐state current is observed, but the interface presents a resonant behavior, i.e., there is no spontaneous oscillation, but the current is prone to oscillate upon applying a small perturbation. When the perturbation is turned off, the oscillations decay, and the steady‐state current is recovered. In this potential range, the impedance exhibits very peculiar characteristics: though the response is linear, a resonant response is found for an excitation at the natural oscillation frequency as well as at its overtones. This can be accounted for in a picture of an electrode surface partitioned into small self‐oscillating domains, uncorrelated in the steady state, but synchronized by the potential excitation. The corresponding “synchronization” contribution to the Faradaic impedance can be computed in the framework of a specific model. This model accounts semiquantitatively for the presence of multiple resonances and for the main features of the impedance results, with a very limited set of parameters.

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