The properties of nanocrystals are highly dependent on their morphology, composition and structure. To obtain full control over their properties, the behavior of nanocrystals under external stimuli, such as heat treatment, needs to be understood. Herein, to in situ observe their microstructure and morphology changes, Fe₃O₄–Ag heterodimers were selected as a model system. Their structural changes after heat treatment were investigated by in situ transmission electron microscopy. A combination of real-time imaging with elemental analysis enabled observation of the transformation of Fe₃O₄–Ag heterodimers having a loose interface configuration to those with a Janus structure at the atomic scale after heating from room temperature to 600 °C. After incubation at 600 °C for 32 min, two kinds of Janus structures could be seen, including a clear linear interface in the Fe₃O₄–Ag heterodimers and a semi-crescent-shaped interface between the Ag and Fe₃O₄ nanoparticles (NPs). These dynamic observations provide unique insights into NP growth mechanisms, which are essential for understanding and controlling the structure and morphology of nanoparticles.

中文翻译：

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Fe 3 O 4 -Ag纳米粒子生长过程的原位透射电镜观察

纳米晶体的性质高度依赖于它们的形态，组成和结构。为了完全控制其性能，需要了解纳米晶体在外部刺激（例如热处理）下的行为。在本文中，为了现场观察其微观结构和形态变化，选择了Fe ₃ O ₄ -Ag异二聚体作为模型系统。通过原位透射电子显微镜研究了热处理后它们的结构变化。实时成像与元素分析相结合，可以观察到Fe ₃ O ₄的转变从室温加热到600°C后，Ag异二聚体与原子级Janus结构的那些具有疏松的界面结构。在600°C下温育32分钟后，可以看到两种Janus结构，包括Fe ₃ O ₄ -Ag异二聚体中清晰的线性界面和Ag与Fe ₃ O ₄纳米颗粒之间的半月牙形界面（NP）。这些动态观察提供了对NP生长机制的独特见解，这对于理解和控制纳米颗粒的结构和形态至关重要。