Abstract Directional solidification from mono-crystalline Si seeds having different orientations along the growth direction is studied. Due to the frequent twinning phenomenon, new grains soon nucleate during growth. The grain competition is then characterized in situ by imaging the dynamic evolution of the grain boundaries and of the corresponding grain boundary grooves that are formed at the solid-liquid interface. To perform this study, an experimental investigation based on Bridgman solidification technique coupled with in situ X-ray imaging is conducted in an original device: GaTSBI (Growth at high Temperature observed by X-ray Synchrotron Beam Imaging). Imaging characterisation techniques using X-ray synchrotron radiation at ESRF (European Synchrotron Radiation Facility, Grenoble, France) are applied during the solidification to study the growth dynamics. Facetted/facetted grain boundary grooves only are studied due to their importance in the grain competition because of their implication in the twinning mechanism. The maximum undercooling inside the groove is calculated from the groove depth knowing the local temperature gradient. Additionally, thanks to dynamic X-ray images, the global solid-liquid interface growth rate and the normal growth rate of the {1 1 1} facets existing at the grooves and at the edges are measured. From these measurements, experimental growth laws that correlate the normal velocity of the {1 1 1} facets with the maximum undercooling of the groove are extracted and compared to existing theoretical models. Finally, the experimental laws found for the contribution to the undercooling of the {1 1 1} facets are in good agreement with the theoretical model implying nucleation and growth eased by the presence of dislocations. Moreover, it is shown that, for the same growth parameters, the undercooling at the level of the facets (always lower than 1 K) is higher at the edges so that there is a higher probability of twin nucleation at the edges which is in agreement with the grain structure development characterised in the present experiments as well as in the literature.

中文翻译：

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{111} 硅结晶过程中的晶面生长规律和晶粒竞争

摘要 研究了沿生长方向具有不同取向的单晶硅晶种的定向凝固。由于频繁的孪晶现象，新晶粒在生长过程中很快成核。然后通过对晶界和在固-液界面处形成的相应晶界凹槽的动态演变进行成像来原位表征晶粒竞争。为了进行这项研究，基于布里奇曼凝固技术结合原位 X 射线成像的实验研究在原始设备 GaTSBI（X 射线同步加速器束成像观察到的高温生长）中进行。在 ESRF（欧洲同步辐射设施，格勒诺布尔，France) 在凝固过程中被用来研究生长动态。刻面/刻面晶界凹槽仅由于它们在孪晶机制中的含义而在晶粒竞争中的重要性而被研究。凹槽内的最大过冷度是根据已知局部温度梯度的凹槽深度计算得出的。此外，由于动态 X 射线图像，测量了存在于凹槽和边缘处的 {1 1 1} 面的整体固液界面生长速率和正常生长速率。从这些测量中，提取了将 {1 1 1} 小平面的法向速度与凹槽的最大过冷度相关联的实验生长规律，并与现有的理论模型进行了比较。最后，{1 1 1} 面的过冷贡献的实验规律与理论模型非常一致，这意味着由于位错的存在，成核和生长得到缓解。此外，结果表明，对于相同的生长参数，小平面水平的过冷度（始终低于 1 K）在边缘处更高，因此在边缘处双核形成的可能性更高，这是一致的在本实验以及文献中表征的晶粒结构发展。