Evolution of small defect clusters in ion-irradiated 3C-SiC: Combined cluster dynamics modeling and experimental study

Abstract

Distribution of black spot defects and small clusters in 1 MeV krypton irradiated 3C-SiC has been investigated using advanced scanning transmission electron microscopy (STEM) and TEM. We find that two thirds of clusters smaller than 1 nm identified in STEM are invisible in TEM images. For clusters that are larger than 1 nm, STEM and TEM results match very well. A cluster dynamics model has been developed for SiC to reveal processes that contribute to evolution of defect clusters and validated against the (S)TEM results. Simulations showed that a model based on established properties of point defects (PDs) generation, reaction, clustering, and cluster dissociation, is unable to predict black spot defects distribution consistent with STEM observations. This failure suggests that additional phenomena not included in a simple pointdefect picture may contribute to radiation-induced evolution of defect clusters in SiC and using our model we have determined the effects of a number of these additional phenomena on cluster evolution. Using these additional phenomena it is possible to fit parameters within physically justifiable ranges that yield agreement between cluster distributions predicted by simulations and those measured experimentally.2 Keywords: silicon carbide, black spot defects, cluster dynamics, STEM, TEM, size distribution 22]. This assumption is also adequate for small clusters, which are neither spherical nor planar [23]. The absorption rate is then defined as [12,14]

Experimental observation of the number of visible defects produced in individual primary damage cascades in irradiated tungsten

“…Note that the average number of visible defects per cascade is order 0.1-0.3, indicating that most cascades do not produce any visible defects. We observe that smallerand therefore also fainter-spots are more difficult to confidently identify on the micrograph, a conclusion also reached recently by Liu et al [17]. Figure 2 makes it plain that the 'count' and 'average' diameter of defects are both functions of the intensity threshold used.…”

Damage microstructure evolution of helium ion irradiated SiC under fusion relevant temperatures

“…Figure 2 shows a sequence of BF-TEM images of SiC irradiated to 5.0 DPA at an irradiation temperature of 400°C. It can be seen from the images that, as the irradiation dose increases, there is an increase in so-called "black spot" damage accumulation which has been observed in SiC under irradiation previously and is attributed to interstitial clusters [31], [32]. These black spots, however, do not appear to grow in size and remain ~5 nm in diameter up to 5.0 DPA.…”

Direct observation of the spatial distribution of primary cascade damage in tungsten

“…There is a minimum observable defect size in a TEM experiment, where the intensity of the defect becomes undetectable from background noise and, concurrently, the resolution limit of the microscope is reached. It is generally considered that, under our imaging conditions, defects of diameter < 1.5nm can not be seen, and for diameter < 2nm the count is likely to be low [9,38] For this work we assume that we see only defects with diameter > 2nm, ( n ≥ 55 ), whereas in the MD simulations we were taking into account defect clusters containing more than n ≥ 13. The apparent reduced size of defects in MD is actually just an artefact of the small number of simulations performed [6,9].…”