Hu Shengyong, Hu Kuo-Juei, Zhao Zixiang, Zhang Yongxin, Shah Syed Adil, Lu Siqi, Zhu Wuwen, Tang Sichen, Song Fengqi
National Laboratory of Solid State Microstructures, Collaborative Innovation Center of Advanced Microstructures, School of Physics, Nanjing University, Nanjing 210093, China.
Institute of Atom Manufacturing Suzhou Campus, Department, Nanjing University, Nanjing 215163, China.
Nanoscale. 2024 Oct 10;16(39):18399-18409. doi: 10.1039/d4nr02111h.
The investigation of nanocluster behaviors at elevated temperatures is important because it encompasses temperature-dependent structural evolution and size-dependent melting points. Size-selected Au, Au, Au, and Au clusters were generated using a gas-phase condensation cluster beam source equipped with a lateral time-of-flight mass selector. Comprehensive heating characterization was conducted, revealing the structural evolution and size-dependent melting point depression of Au clusters at atomic resolution aberration-corrected scanning transmission electron microscopy (AC-STEM). Using quantitative (Q)STEM simulations, a comprehensive statistical analysis was conducted to investigate the structural characteristics of the Au clusters. These clusters tended to be kinetically trapped in metastable structures during nucleation, which subsequently served as "growth templates" for the formation of many metastable Au clusters. heating experiments performed on Au revealed a structural evolution trend from icosahedron (Ih) to decahedron (Dh) and finally to face-centered cubic (FCC) structures, with noticeable competition being observed between the Dh and FCC structures. AC-STEM imaging revealed that the melting of the Au clusters began with the formation of molten liquid shells on the surface. The liquid shells thickened at higher temperatures, and the solid core suddenly melted when its diameter decreased to a critical size. Furthermore, the melting points of the Au clusters were linearly dependent on the reciprocal diameter. Compared with the theoretical models, it was found that the liquid nucleation and growth model is in good agreement with the experimental results, indicating its suitability for describing the surface core melting processes of Au clusters at the studied scales.
对纳米团簇在高温下行为的研究很重要，因为它涉及温度依赖性结构演变和尺寸依赖性熔点。使用配备横向飞行时间质量选择器的气相冷凝团簇束源生成了尺寸选择的Au、Au、Au和Au团簇。进行了全面的加热表征，在原子分辨率的像差校正扫描透射电子显微镜（AC-STEM）下揭示了Au团簇的结构演变和尺寸依赖性熔点降低。使用定量（Q）STEM模拟，进行了全面的统计分析以研究Au团簇的结构特征。这些团簇在成核过程中往往在动力学上被困在亚稳结构中，随后这些亚稳结构成为许多亚稳Au团簇形成的“生长模板”。对Au进行的加热实验揭示了从二十面体（Ih）到十面体（Dh），最终到面心立方（FCC）结构的结构演变趋势，在Dh和FCC结构之间观察到明显的竞争。AC-STEM成像表明，Au团簇的熔化始于表面形成熔融液壳。液壳在较高温度下变厚，当固体核心直径减小到临界尺寸时突然熔化。此外，Au团簇的熔点与直径的倒数呈线性相关。与理论模型相比，发现液核化和生长模型与实验结果吻合良好，表明其适用于描述所研究尺度下Au团簇的表面核心熔化过程。
