Lai King C, Chen Minda, Williams Benjamin, Han Yong, Tsung Chia-Kuang, Huang Wenyu, Evans James W
Ames Laboratory-USDOE, Division of Chemical & Biological Sciences, and Department of Physics & Astronomy, Iowa State University, Ames, Iowa 50011, United States.
Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States.
ACS Nano. 2020 Jul 28;14(7):8551-8561. doi: 10.1021/acsnano.0c02864. Epub 2020 Jul 15.
Stability against reshaping of metallic fcc nanocrystals synthesized with tailored far-from-equilibrium shapes is key to maintaining optimal properties for applications such as catalysis. Yet Arrhenius analysis of experimental reshaping kinetics, and appropriate theory and simulation, is lacking. Thus, we use TEM to monitor the reshaping of Pd nanocubes of ∼25 nm side length between 410 °C (over ∼4.5 h) and 440 °C (over ∼0.25 h), extracting a high effective energy barrier of ≈ 4.6 eV. We also provide an analytic determination of the energy variation along the optimal pathway for reshaping that involves transfer of atoms across the nanocube surface from edges or corners to form new layers on side {100} facets. The effective barrier from this analysis is shown to increase strongly with the degree of truncation of edges and corners in the synthesized nanocube. Theory matches experiment for the appropriate degree of truncation. In addition, we perform simulations of a stochastic atomistic-level model incorporating a realistic description of diffusive hopping for undercoordinated surface atoms, thereby providing a visualization of the initial reshaping process.
合成具有定制的远离平衡形状的金属面心立方纳米晶体时，其抗重塑稳定性是维持催化等应用的最佳性能的关键。然而，目前缺乏对实验重塑动力学的阿伦尼乌斯分析以及适当的理论和模拟。因此，我们使用透射电子显微镜（TEM）监测边长约为25 nm的钯纳米立方体在410 °C（约4.5小时）至440 °C（约0.25小时）之间的重塑过程，提取出约4.6 eV的高有效能垒。我们还对沿重塑最佳路径的能量变化进行了解析测定，该路径涉及原子从纳米立方体的边缘或角穿过表面转移，以在{100}侧面形成新层。结果表明，该分析得出的有效能垒随合成纳米立方体边缘和角的截断程度大幅增加。对于适当的截断程度，理论与实验相符。此外，我们对一个随机原子级模型进行了模拟，该模型对低配位表面原子的扩散跳跃进行了真实描述，从而实现了对初始重塑过程的可视化。
