We have investigated in situ and in real-time the formation process of anodic porous alumina on silicon using infrared absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). We have collected IR absorption spectra of the interface between a porous alumina film and a Si substrate to elucidate the chemical processes involved in the porous-alumina formation. On the basis of the detailed analysis of IRAS spectra together with the variation of the anodic current density, we demonstrate that the chemical process at the alumina-Si interface proceeds as follows: As the pore reaches the alumina-Si interfacial region, inhomogeneous etching takes place. It produces small holes or cracks in the "barrier layer" at the bottom of the alumina pore, and through those holes or cracks the electrolyte pours into the vicinity of the Si substrate surface to form SiO2 nanodots. With further anodization, oxidation of the Si substrate surface occurs and finally peels the porous alumina film off the Si substrate. IRAS data are consistent with the results of observation by a field emission scanning electron microscope. The present results show that MIR-IRAS is a powerful tool for in situ monitoring chemical processes at semiconductor-solution interfaces.
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