The Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University , Atlanta, Georgia 30332, United States.
Department of Chemical and Biological Engineering, University of Wisconsin-Madison , Madison, Wisconsin 53706, United States.
Nano Lett. 2017 Jun 14;17(6):3655-3661. doi: 10.1021/acs.nanolett.7b00844. Epub 2017 May 2.
Despite the remarkable success in controlling the synthesis of metal nanocrystals, it still remains a grand challenge to stabilize and preserve the shapes or internal structures of metastable kinetic products. In this work, we address this issue by systematically investigating the surface and bulk reconstructions experienced by a Pd concave icosahedron when subjected to heating up to 600 °C in vacuum. We used in situ high-resolution transmission electron microscopy to identify the equilibration pathways of this far-from-equilibrium structure. We were able to capture key structural transformations occurring during the thermal annealing process, which were mechanistically rationalized by implementing self-consistent plane-wave density functional theory (DFT) calculations. Specifically, the concave icosahedron was found to evolve into a regular icosahedron via surface reconstruction in the range of 200-400 °C, and then transform into a pseudospherical crystalline structure through bulk reconstruction when further heated to 600 °C. The mechanistic understanding may lead to the development of strategies for enhancing the thermal stability of metal nanocrystals.
尽管在控制金属纳米晶体的合成方面取得了显著的成功，但稳定和保护亚稳动力学产物的形状或内部结构仍然是一个巨大的挑战。在这项工作中，我们通过系统地研究在真空中加热至 600°C 时 Pd 凹五边形二十面体经历的表面和体相重构来解决这个问题。我们使用原位高分辨率透射电子显微镜来确定这个远离平衡结构的平衡途径。我们能够捕捉到在热退火过程中发生的关键结构转变，并通过实施自洽平面波密度泛函理论（DFT）计算对其进行了机械合理化。具体来说，凹五边形二十面体在 200-400°C 的范围内通过表面重构演变为规则的二十面体，然后在进一步加热至 600°C 时通过体相重构转变为类球形的晶体结构。这种机械理解可能会导致开发提高金属纳米晶体热稳定性的策略。
