Development of Multichannel Spectroscopic and Macroscopic Ellipsometer

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An ellipsometer equipped with a two-dimensional CCD image sensor as a optical detector has been built specifically. This ellipsometer can provide both spectroscopic and microscopic analysis of thin surface films. The passive films on carbon steels and stainless steels have been analyzed in situ by using the newly designed ellipsometer. The results are summarized as follows :1. An ellipsometer consisting of a white light source (Xe lamp), a collimator, a rotating polarizer, a scanning sample stage, a fixed analyzer, an image expander, a spectrometer, a CCD image sensor, and a CCD controller has been designed and constructed.2. A series of calibration was carried out to eliminate systematic errors of the optical system, after which the performance of the ellipsometer was evaluated ; the minimum acquisition time of one spectrum over the wavelength range of 400 to 800nm is 10ms, the standard deviation of ellipsometric parameters is less than 0.1 degrees, and the spatial resolution is 25mum.3. Degradation processes of passive films on 18Cr-8Ni steels in 0.1M-NaCl was examined. The changes in the optical spectrum for CVD-Fe_2O_3-Cr_2O_3 films during dissolution were measured to discuss the results obtained on real passive films. It was found that the change in spatial distribution of film thickness is significant during the initiation process of pitting.4. Spatial distribution of film thickness and optical constants of passive films on a carbon steel (0.12%C) was measured. A model analysis on pure Fe (ferrite) and Fe_3C (pearlite constituent) provided a good information on the difference in optical constants between the films on ferrite and pearlite structures.