Central Facility for Electron Microscopy, Group of Electron Microscopy of Materials Science, Ulm University, Ulm, Germany.
School of Chemistry, University of Nottingham, University Park, Nottingham, UK.
Nat Chem. 2020 Oct;12(10):921-928. doi: 10.1038/s41557-020-0538-9. Epub 2020 Aug 28.
Knowing how crystals nucleate at the atomic scale is crucial for understanding, and in turn controlling, the structure and properties of a wide variety of materials. However, because of the scale and highly dynamic nature of nuclei, the formation and early growth of nuclei are very difficult to observe. Here, we have employed single-walled carbon nanotubes as test tubes, and an 'atomic injector' coupled with aberration-corrected transmission electron microscopy, to enable in situ imaging of the initial steps of nucleation at the atomic scale. With three different metals we observed three main processes prior to heterogeneous nucleation: formation of crystal nuclei directly from an atomic seed (Fe), from a pre-existing amorphous nanocluster (Au) or by coalescence of two separate amorphous sub-nanometre clusters (Re). We demonstrate the roles of the amorphous precursors and the existence of an energy barrier before nuclei formation. In all three cases, crystal nucleus formation occurred through a two-step nucleation mechanism.
了解晶体如何在原子尺度上成核对于理解和控制各种材料的结构和性质至关重要。然而，由于核的规模和高度动态性质，核的形成和早期生长非常难以观察。在这里，我们使用单壁碳纳米管作为试管，并采用“原子注射器”结合像差校正的透射电子显微镜，实现了在原子尺度上对成核初始步骤的原位成像。使用三种不同的金属，我们观察到在异质成核之前有三个主要过程：直接从原子种子（Fe）、从预先存在的无定形纳米团簇（Au）或通过两个独立的无定形亚纳米簇（Re）的聚合并成晶体核。我们证明了无定形前体的作用以及在核形成之前存在能量势垒。在所有三种情况下，晶体核的形成都通过两步成核机制发生。
