Study Of The Ion-beam-induced Amorphization In Nanocrystalline SiC

Silicon carbide(SiC)is a structural material which has a great potential in advanced nuclear energy systems.It is of great significance to improve the radiation resistance of SiC for their applications in advanced reactors.Since grain boundaries(GBs)can act as efficient sinks for mobile point defects produced during irradiation,nanocrystalline materials with grain sizes less than 100 nm are expected to be more resistance to radiation as compared with monocrystalline material.To date,there have been only a few studies on the radiation effects in nanocrystalline Si C(nc-SiC),and the related radiation damage mechanism are not well understood.In this work,three types of nc-SiC films with average grain sizes of 2.7 nm,6.0 nm and 19.7 nm and also monocrystalline SiC film were irradiated with 5 MeV Xe,60 keV C and 18 keV He ions respectively at room temperature.The irradiation-induced amorphization of the films was investigated by Raman spectroscopy.The results of Raman spectra show that with increasing ion fluences,the intensities of Si-C peaks gradually decrease,whereas those of Si-Si and C-C peaks from the amorphous structure gradually increase until the irradiated SiC films were completely amorphized.After that,the shape of the spectra keeps almost unchanged with further increasing fluences.The relative intensities of Si-C vibration peaks are used to characterize the relative structural disorder of irradiated SiC films.It is found that:(1)for all the three ion irradiations,the dose needed for the amorphization of nc-SiC increases with increasing grain size,but it is obviously lower than that of monocrystalline Si C.For the Si C grains embedded in an amorphous SiC matrix,the epitaxial growth of the amorphous matrix into the grain interior during irradiation may be the dominant process for the rapid amorphization of SiC grains.(2)at the same atomic displacement dose(dpa),the structural disorders of the nc-Si C films induced by the Xe,C and He ion irradiations are similar,and irradiation of these three ions results in almost the same amorphization rate of the nc-SiC film.This may be due to the facts that the lighter ions have a larger ion flux and the large electron energy deposition of the Xe ions have the effects on the recovery of irradiation defects.Our results show that,for ion irradiations with different ion masses,the radiation resistance of nc-SiC increases with increasing grain size and monocrystalline Si C has a higher radiation resistance compared with nc-SiC.The results may have important implications for the applications of nc-Si C material in future nuclear energy systems.