State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China.
Phys Chem Chem Phys. 2019 Feb 6;21(6):3134-3139. doi: 10.1039/c8cp07576j.
Bimetallic core-shell nanoparticles have received considerable attention for their unique optical, magnetic and catalytic properties. However, these properties will be dramatically modified under ambient conditions by their structure and/or composition change. Thus, it is of primary importance to study the complex transformation pathway of core-shell nanoparticles at an elevated temperature. In this work, by using an aberration-corrected scanning transmission electron microscope equipped with an energy dispersive X-ray mapping system, the complete transformation process from a well-designed Pd@Au core-shell nanoparticle to a uniform alloy particle was visualized. It is revealed that this transformation process went through three steps, i.e., surface refacetting, particle resphering and complete alloying. Combining with a developed atomic kinetic Monte Carlo simulation, we found that surface energy is the driving force for shape variation, and the different atomic activation barriers of surface diffusion and bulk migration result in the multistep transformation pathway. Our results offered important information for understanding the structure evolution of bimetallic core-shell nanoparticles, which is beneficial for the rational design of nanoparticles with kinetic stability.
双金属核壳纳米粒子因其独特的光学、磁学和催化性能而受到广泛关注。然而，在环境条件下，它们的结构和/或组成变化会显著改变这些性质。因此，研究核壳纳米粒子在高温下的复杂转化途径至关重要。在这项工作中，通过使用配备能量色散 X 射线映射系统的校正像差扫描透射电子显微镜，可视化了从精心设计的 Pd@Au 核壳纳米粒子到均匀合金粒子的完整转化过程。结果表明，这个转变过程经历了三个步骤，即表面再构、颗粒回复和完全合金化。结合开发的原子动力学蒙特卡罗模拟，我们发现表面能是形状变化的驱动力，表面扩散和体相迁移的不同原子激活势垒导致了多步转化途径。我们的结果为理解双金属核壳纳米粒子的结构演化提供了重要信息，这有利于具有动力学稳定性的纳米粒子的合理设计。
