Fe
2O
3-Cr
2O
3 thin films were formed on Pt substrates at 623K by low pressure CVD technique using Fe(O
2C
5H
7)
3 and Cr(O
2C
5H
7)
3 as precursors and O
2 as a reaction gas. The dissolution processes of the films under anodic and cathodic polarization in 1kmol·m
-3 H
2SO
4 were examined
in-situ by real-time spectroscopic ellipsometry. Spectra of refractive index
nfilm and extinction coefficient
kfilm of the optical constant of the films,
Nfilm (=
nfilm-
ikfilm), in a wavelength range 470-780nm were measured as a function of dissolution time. When the film with a Cr cationic fraction
XCr=0.26 was polarized at a cathodic potential of 0.0V (vs. Ag/AgCl/3.33kmol·m
-3 KCl), the value of
nfilm in a wavelength range less than 700nm and that of
kfilm in the whole wavelength range decreased with time. This suggests that reductive dissolution of Fe
2O
3 gives rise to an enrichment of Cr
2O
3 in the film, which is followed by an increase in the void fraction of the film. When the film with
XCr=0.61 was polarized at an anodic potential of 1.1V, the value of
nfilm first increased and then decreased with time, while that of
kfilm monotonously decreased with time. The change in
nfilm was prominent in a short wavelength range. These results show that the oxidative dissolution of Cr
2O
3 causes both an enrichment of Fe
2O
3 and an increase in a void fraction or surface roughness. The influence of the enrichment of Fe
2O
3 on
nfilm is ascendant in the initial stage of dissolution and that of the increased void fraction or surface roughness is predominant in the subsequent stage of dissolution.
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