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Degree

Doctor of Philosophy, Case Western Reserve University, Chemistry, 1990.

Abstract

The passive film on iron and its breakdown by chloride ions in borate buffer (pH 8.4) has been studied using in situ UV/VIS spectroscopic ellipsometry and fast step potentiostatic method.

A new highly stabilized light source and an improved computer algorithm have been developed. Interpretation of the ellipsometric measurements are based on the three parameter (3-P) method, which was used to obtain unambiguous solutions for the film.

Errors in the resultant 3-P solutions were found to be caused mainly by the fluctuation and random noise in the reflectivity measurement. A combined 3-P/2-P method was used to minimize this problem. Some insights into the use of the three parameter method are presented. It is concluded that the accuracy of the ellipsometric measurements depend primarily on the accuracy of the film thickness measurement, which in turn depends on the accuracy of the relative reflectivity measurement.

Optical spectra of passive films on iron formed at various potentials are presented. Several distinct features of the spectra were observed: (1) a broad absorption band ranging from 2.5 to 5 eV (photon energy); (2) an absorption peak at 3.5 eV which exists at all potentials but becomes smaller at lower potentials, which is attributed to a Fe_2p→O_3d transition; (3) some unresolvable background absorption; and (4) an evident structure above 5 eV. No fine structures were found. During the potentiostatic reduction in a potential region between 0.4 to 0.2, significant changes were observed in the optical constants. No spectral changes were observed on the passive film due to Cl^-

Subject Headings

Chemistry, Physical

Keywords

passivation iron chloride ions situ spectroscopic ellipsometric technique

Advisor

Boris D. Cahan

Pages

170p.

Document number: case1054563395
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=case1054563395

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