Li Zhe, Chen Hsin-Yi Tiffany, Schouteden Koen, Picot Thomas, Liao Ting-Wei, Seliverstov Aleksandr, Van Haesendonck Chris, Pacchioni Gianfranco, Janssens Ewald, Lievens Peter
State Key Laboratory on Tunable Laser Technology, Ministry of Industry and Information Technology Key Lab of Micro-Nano Optoelectronic Information System, School of Science, Harbin Institute of Technology, Shenzhen 518055, China.
Department of Engineering and System Science, National Tsing Hua University, Hsinchu 30013, Taiwan.
Sci Adv. 2020 Jan 3;6(1):eaay4289. doi: 10.1126/sciadv.aay4289. eCollection 2020 Jan.
The free-standing Au cluster has a unique tetrahedral shape and a large HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gap of around 1.8 electron volts. The "magic" Au has been intensively used as a model system for understanding the catalytic and optical properties of gold nanoclusters. However, direct real-space ground-state characterization at the atomic scale is still lacking, and obtaining fundamental information about the corresponding structural, electronic, and dynamical properties, is challenging. Here, using cluster-beam deposition and low-temperature scanning tunneling microscopy, atom-resolved topographic images and electronic spectra of supported Au clusters are obtained. We demonstrate that individual size-selected Au on ultrathin NaCl films maintains its pyramidal structure and large HOMO-LUMO gap. At higher cluster coverages, we find sintering of the clusters via Smoluchowski ripening to Au agglomerates. The evolution of the electron density of states deduced from the spectra reveals gap reduction with increasing agglomerate size.
独立的金团簇具有独特的四面体形状，其最高占据分子轨道与最低未占据分子轨道（HOMO-LUMO）之间的能隙约为1.8电子伏特。“神奇”的金已被广泛用作理解金纳米团簇催化和光学性质的模型体系。然而，目前仍缺乏原子尺度上直接的实空间基态表征，获取有关相应结构、电子和动力学性质的基本信息具有挑战性。在此，利用团簇束沉积和低温扫描隧道显微镜，获得了负载型金团簇的原子分辨形貌图像和电子能谱。我们证明，在超薄氯化钠薄膜上单个尺寸选择的金团簇保持其金字塔结构和较大的HOMO-LUMO能隙。在更高的团簇覆盖率下，我们发现团簇通过斯莫卢霍夫斯基熟化烧结成金团聚体。从能谱推导出的态密度演化表明，随着团聚体尺寸的增加，能隙减小。
