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Conference Article: Silver Ion Implantation and Annealing In Cvd Silicon Carbide: The Effect of Temperature on Silver Migration

Heather J. MacLean, Ronald G. Ballinger, MIT, Cambridge, USA

Abstract

The effect of temperature on the migration of silver in CVD β-SiC has been studied using ionimplantation. Silver ions with were implanted in ß SiC using the ATLAS accelerator facility at the Argonne National Laboratory. Ion beams with energies of 93 and 161 MeV were used to achieve deposition with peak concentrations at approximately 9 and 13 µm depth respectively. As-implanted samples were then annealed at 1500°C for 210 and 480 hours. XPS, SEM, TEM, STEM, and optical methods were used to analyze the material before and after annealing. Silver concentration profiles were determined using XPS before and after annealing. STEM and SEM equipped with quantitative chemical analysis capability were used to more fully characterize the location and morphology of the silver before and after annealing. The results show that, within the uncertainty of measurement techniques, there is no silver migration, either inter or intra-grannular, for the times and temperature studied. Additionally, the silver was observed to phase separate within the SiC after annealing. The irradiation damage from the implantation process resulted in a three-layer morphology in the as-implanted condition: (1) a layer of unaltered SiC followed by (2) a layer of crystallized SiC, followed by (3) an amorphized layer which contained essentially all of the implanted silver. After annealing the layer structure changed. Layer 1 was unaltered. Layer 2 recrystallized to form an epitaxial (columnar) layer. Layer 3 recrystallized to form a fine grain equiaxed layer. The results of this work does not support the long held assumption that silver migrates by grain boundary diffusion in CVD SiC used for gas reactor coated particle fuel.

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key words: Ion Implantation, Silver Diffusion, Silicon Carbide
Reference:
Proceedings of the Conference on High Temperature Reactors, Beijing, China, September, 22-24, 2004
International Atomic Energy Agency, Vienna (Austria)
HTR-2004, pp:1-20