Xia Weiwei, Yang Yang, Meng Qingping, Deng Zhiping, Gong Mingxing, Wang Jie, Wang Deli, Zhu Yimei, Sun Litao, Xu Feng, Li Ju, Xin Huolin L
SEU-FEI Nano-Pico Center, Key laboratory of MEMS of Ministry of Education , Southeast University , Nanjing 210096 , China.
Department of Nuclear Science and Engineering and Department of Materials Science and Engineering , Massachusetts Institute of Technology , Cambridge , Massachusetts 02139 , United States.
ACS Nano. 2018 Aug 28;12(8):7866-7874. doi: 10.1021/acsnano.8b02170. Epub 2018 Aug 13.
The formation of hollow-structured oxide nanoparticles is primarily governed by the Kirkendall effect. However, the degree of complexity of the oxidation process multiplies in the bimetallic system because of the incorporation of more than one element. Spatially dependent oxidation kinetics controls the final morphology of the hollow nanoparticles, and the process is highly dependent on the elemental composition. Currently, a theoretical framework that can predict how different metal elements result in different oxide morphologies remains elusive. In this work, utilizing a combination of state-of-the-art in situ environmental transmission electron microscopy and three-dimensional (3D) chemically sensitive electron tomography, we provide an in situ and 3D investigation of the oxidation mechanism of the Ni-Fe nanoparticles. The direct measurements allow us to correlate the 3D elemental segregation in the particles with the oxidation morphologies, that is, single-cavity or dual-cavity hollow structure, and multicavity porous structures. Our findings in conjunction with theoretical calculations show that metal concentration, diffusivity, and particle size are important parameters that dictate the mechanical and phase stabilities of the hollow oxide shell, which in turn determine its barrier properties and the final hollow oxide morphology. It sheds light on how to use multielemental oxidation to control morphology in nanomaterials and demonstrates the power of 3D chemical imaging.
中空结构氧化物纳米颗粒的形成主要受柯肯达尔效应控制。然而，由于双金属体系中包含不止一种元素，氧化过程的复杂程度成倍增加。空间相关的氧化动力学控制着中空纳米颗粒的最终形态，并且该过程高度依赖于元素组成。目前，一个能够预测不同金属元素如何导致不同氧化物形态的理论框架仍然难以捉摸。在这项工作中，我们结合了最先进的原位环境透射电子显微镜和三维（3D）化学敏感电子断层扫描技术，对镍铁纳米颗粒的氧化机制进行了原位三维研究。直接测量使我们能够将颗粒中的三维元素偏析与氧化形态相关联，即单腔或双腔中空结构以及多腔多孔结构。我们的研究结果与理论计算表明，金属浓度、扩散率和颗粒尺寸是决定中空氧化物壳层力学和相稳定性的重要参数，而这反过来又决定了其阻隔性能和最终的中空氧化物形态。它阐明了如何利用多元素氧化来控制纳米材料的形态，并展示了三维化学成像的强大功能。
