Effects of electronic and nuclear interactions in SiC

doi:10.1016/j.nimb.2009.02.033

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 267, Issue 6, March 2009, Pages 976-979

https://doi.org/10.1016/j.nimb.2009.02.033 Get rights and content

Abstract

In this study, we performed irradiation experiments on nanostructured 3C–SiC samples, with 95 MeV Xe ions at room temperature. This energy permits the observation of the combined electronic and nuclear interactions with matter. The grazing incidence X-ray diffraction results do not reveal a complete amorphization, despite value of displacement per atom overcoming the total amorphization threshold. This may be attributed to competing effects between nuclear and electronic energy loss in this material since a total amorphization induced by nuclear interactions was found after low energy ion irradiation (4 MeV Au). Moreover, electronic interactions created by high energy ion irradiations induce no disorder in single crystalline 6H–SiC. But in samples previously disordered by low energy ion implantation (700 keV I), the electronic interactions generate a strong defects recovery.

Introduction

The aim of this paper is to study the structural evolution of silicon carbide under ion irradiation. Numerous studies have been already performed with low energy ions in order to observe the nuclear interaction effects on single 6H–SiC crystals. They have shown a rapid amorphization during irradiation at room temperature (RT) [1]. On the other hand, only few studies concern the electronic interaction effects. They indicate a very low disordering of virgin samples under high energy ion irradiation at RT and a defects recovery of predamaged samples under 827 MeV Pb irradiations [2].

Beside the peculiar properties of SiC, its elaboration as a nanostructured ceramic (NSC) is also worth studying because of the high grain boundaries density that is expected to provide an efficient source of traps for irradiation induced defects [3], but the enhancement of the behaviour under irradiation has still to be proven.

The present work is focussed on the structural evolution of NSC–SiC samples under irradiation at RT with 95 MeV Xe delivered by the IRRSUD line of the GANIL facility. These ions are similar to fission products and allow the observation of the combined electronic and nuclear interactions with matter. To study separately the nuclear and the electronic interactions effects, the samples were irradiated with 4 MeV Au ions on the ARAMIS accelerator of the CSNSM and 910 MeV Xe ions delivered by the GANIL.

Section snippets

Experimental

3C–SiC nanopowders with an average grain size of 10 nm were synthesized by the laser pyrolysis technique [4], [5], which allows an accurate control of the granulometry and stoichiometry. Using these nanopowders, two ceramic samples were subsequently prepared by hot isostatic pressing (HIP) without sintering additives. The densification of the final NSC–SiC pellet is close to 92% with a grain size after sintering around 36 nm.

The first pellet was irradiated at RT with 95 MeV Xe ions and a fluence

Results and discussion

The results obtained from XRD on the nanostructured samples before irradiation for a probed depth of 2.5 μm (Fig. 1) clearly show the cubic phase of SiC. The slight contribution at 2θ = 34.2° could be attributed to the hexagonal phase. This contribution is in fact the consequence of stacking faults in some crystallites of the starting nanopowders [6]. Fig. 1 also exhibits the typical peak broadening coming from the nanometric size of the crystallites [7], [8].

The samples were irradiated with 95 MeV

Conclusion

Nanostructured 3C–SiC samples were irradiated at RT with 95 MeV Xe ions and no large scale amorphization could be detected in spite of a number of dpa exceeding the amorphization threshold found in literature with low energy ions. However, a complete sample amorphization was noticed after irradiation at RT with low energy ions (4 MeV Au), where the nuclear interactions are dominant. The absence of amorphization under 95 MeV Xe ions irradiation is assumed to be the consequence of the competing

Acknowledgements

The authors thank the DEN/DMN/SRMA/LTMEX Laboratory for the pellets sintering.

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Past studies have shown that Se for SHI irradiations can induce annealing of pre-existing defects [32,33,57,58], and total damage suppression is observed in pristine, single crystal SiC irradiated with SHIs. Partial suppressions of damage accumulation has been observed in nano-grained SiC irradiated with 95 MeV Xe ions (Se = 14 keV/nm) [59]; however, the depth dependence damage suppression and role of the nano-grained structure versus high Se on damage suppression are unknown at this time. Determining the threshold conditions for complete suppression for irradiation-induced disordering at high energies for higher Z ions, including SHIs, will be experimentally challenging, because the onset of damage accumulation requires high fluences, should be close to the surface to be observed, and requires incremental energy steps of a few MeV to explore a wide energy range.
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