Li Junjie, Chen Jiangchun, Wang Hua, Chen Na, Wang Zhongchang, Guo Lin, Deepak Francis Leonard
Department of Advanced Electron Microscopy Imaging and Spectroscopy International Iberian Nanotechnology Laboratory (INL) Avenida Mestre Jose Veiga 4715-330 Braga Portugal.
School of Chemistry and Environment Beihang University Beijing 100191 China.
Adv Sci (Weinh). 2018 Mar 27;5(6):1700992. doi: 10.1002/advs.201700992. eCollection 2018 Jun.
Understanding classical and nonclassical mechanisms of crystal nucleation and growth at the atomic scale is of great interest to scientists in many disciplines. However, fulfilling direct atomic-scale observation still poses a significant challenge. Here, by taking a thin amorphous bismuth (Bi) metal nanosheet as a model system, direct atomic resolution of the crystal nucleation and growth initiated from an amorphous state of Bi metal under electron beam inside an aberration-corrected transmission electron microscope is provided. It is shown that the crystal nucleation and growth in the phase transformation of Bi metal from amorphous to crystalline structure takes place via the particle-mediated nonclassical mechanism instead of the classical atom-mediated mechanism. The dimension of the smaller particles in two contacted nanoparticles and their mutual orientation relationship are critical to governing several coalescence pathways: total rearrangement pathway, grain boundary migration-dominated pathway, and surface migration-dominated pathway. Sequential strain analyses imply that migration of the grain boundary is driven by the strain difference in two Bi nanocrystals and the coalescence of nanocrystals is a defect reduction process. The findings may provide useful information to clarify the nanocrystal growth mechanisms of other materials on the atomic scale.
理解原子尺度下晶体成核和生长的经典与非经典机制，是许多学科的科学家们极为感兴趣的。然而，实现直接的原子尺度观测仍然面临重大挑战。在此，通过以薄的非晶态铋（Bi）金属纳米片作为模型系统，在像差校正透射电子显微镜内的电子束作用下，提供了从Bi金属的非晶态起始的晶体成核和生长的直接原子分辨率。结果表明，Bi金属从非晶态到晶体结构的相变中的晶体成核和生长是通过粒子介导的非经典机制而非经典的原子介导机制发生的。两个接触的纳米颗粒中较小颗粒的尺寸及其相互取向关系对于控制几种聚结途径至关重要：完全重排途径、以晶界迁移为主的途径和以表面迁移为主的途径。连续应变分析表明，晶界的迁移是由两个Bi纳米晶体中的应变差异驱动的，并且纳米晶体的聚结是一个缺陷减少过程。这些发现可能为在原子尺度上阐明其他材料的纳米晶体生长机制提供有用信息。
