Effect Of Heat Treatment On The Migration Behaviour Of Selenium Implanted Into Polycrystalline Sic

This study reviews the migration behaviour of selenium in polycrystalline SiC, which acts as the main diffusion barrier in the coated fuel particles for Very High Temperature Reactors. Se ions of 200 keV were implanted into polycrystalline SiC wafers to a fluence of 1 x 1016 cmi 2 at three temperatures, which were room temperature, 350 degrees C and 600 degrees C. The implanted samples were annealed at temperatures ranging from 1000 to 1500 degrees C in steps of 100 degrees C for 10 h. The migration of implanted Se was monitored by Rutherford backscattering spectrometry (RBS) while structural and morphological changes were monitored by Raman spectroscopy and scanning electron microscopy (SEM). Implantation of Se at room temperature amorphized the near surface region of the SiC substrates, while in samples implanted above the critical amorphization temperature the crystal structure was retained with some radiation damage. Annealing at 1000 degrees C resulted in the recrystallization of the amorphized SiC layer. In the case of room temperature implantation, the broadening of the implanted Se profile in RBS spectra was observed to occur after annealing at 1300 degrees C and became significant with an increase in annealing temperature. This broadening was accompanied by a peak shift towards the surface and loss of implanted Se. No broadening was observed in samples implanted above the critical amorphization temperature, but the peak shift towards the surface began after annealing at 1300 degrees C in samples implanted at 350 degrees C and 600 degrees C.