In Part I of this work, the bias dependence of the etching of silicon (111) has been investigated by means of in situscanning tunneling microscopy observations. In this second part, current‐voltage curves and etch rate results derived from the loss of material and performed with n‐type Si samples of various orientations, show that electrochemical and chemical reactions coexist in the oxidation of Si. A model is presented for the oxidation of a Si atom in a kink site in different situations of polarization. The key feature of the description is the understanding of the persistent hydrogen termination of the surface in spite of the continuous oxidative removal of Si atoms from the surface. The model includes the hydrolytic splitting of Si—H and Si—Si bonds as the important chemical contributions to the etching process. At the rest potential, the chemical component is dominant. The sequence of reactions leaves the surface in the false(1×1false)‐H terminated state. The anodic current is due to the injection of electrons which are produced during the substitution of Si—H by Si—OH bonds. This results above a critical electrode potential in passivation. In this respect, (111) and (100) faces present quite different behaviors. At cathodic bias where the hydrogen evolution becomes fast, due to the accumulation of electrons at the surface, not only the anodic component of the etching reaction vanishes but also the chemical component decreases in rate and is eventually stopped.

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The etching of n-type silicon (111) has been investigated by means of in situ scanning tunneling microscopy (STM) observations performed over a wide range of bias of the sample. A special procedure has been used to observe topography changes at potentials close and positive of the rest potential. Irrespective of the bias, images show that the surface consists in atomically smooth terraces separated by 3.1/~ high steps. At cathodic bias, the etching occurs principally at terrace edges and (111) terraces are most probably H terminated, which prevents their reconstruction, as could be seen in atomically resolved pictures taken in situ. Triangular etch pits nucleate when the potential approaches the rest potential. The Si-H coverage is, however, preserved despite the continuous removal of Si atoms from the surface. Beyond the passivation potential, a high density of etch pits is developed on the terraces, although the dissolution rate decreases. It is shown that the etch rate of the dissolution can be derived from sequences of STM images and that it presents a maximum, close to the rest potential, as it has been found previously with long-term material loss measurements. The present STM results yield new insights into the surface chemistry and the anisotropy of the reaction. The complementary electrochemical characterization of the etching process will be outlined in Part II of this paper (the following article) where a detailed reaction mechanism is presented.

The present experience of the electrochemical dissolution of silicon and previous assumptions upon the mechanism are briefly reviewed. A new model is developed which explains how the coverage of the surface by hydrogen can be maintained in spite of the continuous anodic dissolution.