Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
7968440 | Journal of Nuclear Materials | 2014 | 10 Pages |
Abstract
Dielectric mirrors of HfO2/SiO2 and Al2O3/SiO2 designed for optimum reflectivity at 248Â nm with 11 and 30 bi-layer coatings, respectively, survived irradiation to 0.1Â dpa at 448Â K without film cracking or delamination from their sapphire substrates. Subsequent annealing of the irradiated samples resulted in a loss of reflectivity in the HfO2/SiO2 mirror, while the Al2O3/SiO2 type remained unaffected. Microstructural changes that correlate to optical property changes of the mirror are investigated. The amorphous layers of the Al2O3/SiO2 mirror provide greater stability despite increased Al and Si interdiffusion across the film interfaces with increasing dose and post-irradiation annealing temperature. This interdiffusion may have limited the densification of SiO2 in the Al2O3/SiO2 mirror, but no interdiffusion was observed for the HfO2/SiO2 mirror. The thickness changes in the SiO2 layers of the HfO2/SiO2 mirror resulted in a shifting of the peak reflectivity to lower wavelengths. The formation of an amorphous Al-O layer within the substrate is observed in the 0.1Â dpa irradiated HfO2/SiO2 mirror, which on further annealing at 573 and 673Â K resulted in a buckling-type delamination failures in the mirrors producing a loss in reflectivity.
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Authors
Keith J. Leonard, Gerald E. Jellison, N.A.P. Kiran Kumar, Lance L. Snead,