Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK.
Chemistry and Industrial Chemistry Department, University of Genoa, Via Dodecaneso 31, 16146, Genoa, Italy.
Nat Commun. 2018 Apr 3;9(1):1323. doi: 10.1038/s41467-018-03794-9.
The equilibrium structures and dynamics of a nanoscale system are regulated by a complex potential energy surface (PES). This is a key target of theoretical calculations but experimentally elusive. We report the measurement of a key PES parameter for a model nanosystem: size-selected Au nanoclusters, soft-landed on amorphous silicon nitride supports. We obtain the energy difference between the most abundant structural isomers of magic number Au clusters, the decahedron and face-centred-cubic (fcc) structures, from the equilibrium proportions of the isomers. These are measured by atomic-resolution scanning transmission electron microscopy, with an ultra-stable heating stage, as a function of temperature (125-500 °C). At lower temperatures (20-125 °C) the behaviour is kinetic, exhibiting down conversion of metastable decahedra into fcc structures; the higher state is repopulated at higher temperatures in equilibrium. We find the decahedron is 0.040 ± 0.020 eV higher in energy than the fcc isomer, providing a benchmark for the theoretical treatment of nanoparticles.
纳米系统的平衡结构和动力学由复杂的势能面（PES）调节。这是理论计算的一个关键目标，但在实验中难以实现。我们报告了对模型纳米系统的关键 PES 参数的测量：软着陆在非晶硅氮化物载体上的尺寸选择的金纳米团簇。我们从最丰富的魔术数 Au 团簇的结构异构体（即二十面体和面心立方（fcc）结构）的平衡比例中获得了这些异构体之间的能量差。通过原子分辨率扫描透射电子显微镜，在超稳定加热台上，在温度（125-500°C）下进行测量。在较低温度（20-125°C）下，该行为是动力学的，表现为亚稳态二十面体向 fcc 结构的向下转换；在较高温度下，平衡时较高的状态重新填充。我们发现二十面体比 fcc 异构体高出 0.040 ± 0.020 eV，为纳米颗粒的理论处理提供了基准。
