Key Laboratory for the Physics and Chemistry of Nanodevices and Department of Electronics, Peking University, Beijing 100871, P.R. China.
National Center for Electron Microscopy in Beijing, School of Materials Science and Engineering, The State Key Laboratory of New Ceramics and Fine Processing, Key Laboratory of Advanced Materials (MOE), Tsinghua University, Beijing 100084, P.R. China.
Sci Rep. 2017 Jan 18;7:40911. doi: 10.1038/srep40911.
Catalyst-free methods are important for the fabrication of pure nanowires (NWs). However, the growth mechanism remains elusive due to the lack of crucial information on the growth dynamics at atomic level. Here, the noncatalytic growth process of ZnO NWs is studied through in situ high resolution transmission electron microscopy. We observe the layer-by-layer growth of ZnO nanopillars along the polar [0001] direction under electron beam irradiation, while no growth is observed along the radial directions, indicating an anisotropic growth mechanism. The source atoms are mainly from the electron beam induced damage of the sample and the growth is assisted by subsequent absorption and then diffusion of atoms along the side surface to the top (0002) surface. The different binding energy on different ZnO surface is the main origin for the anisotropic growth. Additionally, the coalescence of ZnO nanocrystals related to the nucleation stage is uncovered to realize through the rotational motions and recrystallization. Our in situ results provide atomic-level detailed information about the dynamic growth and coalescence processes in the noncatalytic synthesis of ZnO NW and are helpful for understanding the vapor-solid mechanism of catalyst-free NW growth.
无催化剂方法对于纯纳米线 (NWs) 的制造很重要。然而，由于缺乏关于原子水平生长动力学的关键信息，其生长机制仍然难以捉摸。在这里，通过原位高分辨率透射电子显微镜研究了 ZnO NW 的非催化生长过程。我们观察到在电子束辐照下，ZnO 纳米柱沿着极性 [0001] 方向逐层生长，而在径向方向上没有生长，表明存在各向异性生长机制。源原子主要来自于样品的电子束诱导损伤，并且生长过程中，原子随后沿着侧面吸收并扩散到顶部 (0002) 表面，从而得到辅助。不同 ZnO 表面上的不同结合能是各向异性生长的主要原因。此外，还揭示了与成核阶段相关的 ZnO 纳米晶的合并是通过旋转运动和再结晶来实现的。我们的原位结果提供了关于非催化合成 ZnO NW 中动态生长和合并过程的原子级详细信息，有助于理解无催化剂 NW 生长的气-固机制。
