Optical characterization of passive oxides on metals

Abstract

In-situ optical detection of the passive oxide films on iron and titanium was reviewed. The optical techniques suc as ellipsometry (i.e., reflection of polarized light), Raman spectroscopy, and potential modulation reflectance (PMR have been successfully applied to the detection in thickness, composition, and semiconducting property respectively, of the thin passive oxides under the in-situ condition. The growth mechanism of the passive oxid has been discussed from the precise measurement of thickness as a function of potential and time by a threeparamete ellipsometry. From the in-situ Raman spectra, the composition of the passive oxide has been estimate to be Fe3O4-y-Fe2O3 for iron and anatase TiO2 for titanium. From PMR, the Mott-Schottky type plot could be drawn i the passive oxide on iron, which indicates that the formation of the space charge layer can be optically seen. Fro the PMR spectra, one has evaluated light-Absorption edge that may correspond to a band-gap energy between th valence and conduction band.