Shiro Matsuda1 and Katsuhisa Sugimoto1
1Department of Metallurgy, Faculty of Engineering, Tohoku University, Sendai
In order to understand the changes of surface oxide films with cathodic polarization of an oxide-covered Ta electrode and with anodic polarization of a hydrogen-absorbed Ta electrode, the ellipsometric parameters have been measured in situ on Ta electrodes under anodic and cathodic polarization in a 0.5 kmol • m-3H2SO4 solution. Optical constants for the film-free surface and the hydrogen-absorbed surface of Ta were determined by tribo-ellipsometry and used to calculate the thickness and optical constants of surface films from measured values of ellipsometric parameters.
When a Ta electrode having an anodic oxide film was polarized to a cathodic potential, the transformation of the film was observed from change in extinction coefficient of the optical constant from zero to about 0.15, while its thickness did not change during prolonged cathodic polarization.
When a hydrogen-absorbed Ta electrode was polarized to an anodic potential, the discharge of hydrogen and the formation of anodic oxide film occurred simultaneously. The optical constant of the anodic oxide film formed on hydrogen-absorbed Ta was smaller than that formed directly on Ta metal.
ellipsometry, tantalum, anodic oxide film, hydrogen-absorption, optical constant, film thickness
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