A STUDY OF THE OPTICAL PROPERTIES OF ZIRCALOY 2 AND 4 AND THEIR OXIDES BY ELLIPSOMETRY

We report here for the first time ellipsometric measurements on the wavelength and temperature dependence of the complex refractive index, n-ik, of Zircaloy 2 and 4; the refractive index n and the extinction coefficient k. These were found to range from 1.135-i1.523 at 0.3131 (mu)m wavelength to 4.846-i7.345 at 3.39 (mu)m. These values are close to those reported in the literature for zirconium. The similarity in values is not unexpected because Zircaloy is approximately 98% zirconium. In the same wavelength range the complex refractive index of Zircaloy oxide was also determined. n varies from 2.3 at 0.3131 (mu)m to about 2.0 at 3.39 (mu)m. These results are also similar to literature values for zirconium oxide. Unlike zirconium oxide, for which we were unable to find published values, the extinction coefficient of Zircaloy oxide was found to be between 0.1 and 0.3, dependent on both temperature and thickness in addition to exhibiting wavelength dispersion. This behavior of the extinction coefficient is undoubtedly related to the structure of the oxide as influenced by temperature and oxide thickness. This and other aspects of oxide formation and behavior can be examined in situ by ellipsometry, which is one of the unique features of the technique. Oxide kinetics could be monitored in real time in a variety of vapor or liquid ambients, as long as the ambient medium allows penetration of the measuring light beam to the surface under study. We expect that it should be possible to measure thicker films if the measuring wavelength is increased. However, we believe that the greatest benefits will derive from in situ studies in real time. Such measurements should reveal useful information on the time-temperature dependence of oxide growth from initial onset of oxidation