衬底表面上贵金属团簇激发态性质的双光子光电子能谱实验研究

Atomic clusters that exhibit quantum confinement effects constitute ideal model systems to investigate fundamental physical and chemical properties of nanostructured materials. Clusters are also promising building blocks for future nano-devices. Among all the properties, the excited states of the clusters play important roles in the nanotechnology-related fields such as catalysis, luminescence, and light-energy conversion. However, the systematical study on the excited-state electronic properties of supported clusters is still lacking...In this project we will focus on small noble metal clusters (e.g. Au clusters, Pt clusters, and Au-Pt binary clusters) composed of one or two types of elements with only tens to hundreds of atoms and with sizes in the order of nanometer. In a cluster beam deposition apparatus, the clusters first will be mass-selected in the gas phase with atomic precision and then deposited onto atomically flat surfaces (e.g. ultrathin NaCl films, and TiO2 surfaces). Using a surface femtosecond time-resolved two-photon photoemission experiments under clean vacuum conditions, we will investigate the excited-state electronic properties (e.g., the electronic structure, the excitation and decay channels, and the lifetime) of the deposited clusters. In particular we will examine how these properties depend on the number of atoms the cluster is composed of as well as on the selected supporting substrate...The investigation on the excited states of supported size-selected clusters provides an opportunity to build a fundamental understanding of the dynamical behavior of the electrons in the cluster-surface system, and may lead to significant development of novel and efficient applications based on clusters.

原子团簇具有优异的物理化学特性，是构筑未来纳米器件的基本单元，其电子激发态在催化、发光、光能转化等过程中发挥重要作用。然而，目前对团簇电子激发态的基本性质以及影响激发态的因素及机理还缺乏系统的研究。. 本项目以一元及二元贵金属团簇为研究对象（如金团簇、铂团簇、金-铂合金团簇等），在高真空环境中，采用质量选择技术将单一尺寸的团簇沉积到表面上（如超薄绝缘层或二氧化钛等），利用时间分辨的飞秒双光子光电子能谱实验，探测团簇-表面体系的电子激发态动力学特性。通过比较不同尺寸的团簇在同一表面上，以及同一尺寸的团簇在不同表面上的电子激发态的电子结构、电子跃迁与弛豫的路径、激发态寿命等关键参数，明晰团簇尺寸和团簇-表面相互作用对团簇激发态性质的影响，为调控衬底表面上团簇的激发态性质和发展基于团簇的新型应用给予重要的基础物理参考。

确定团簇的原子结构及其与衬底表面的相互作用，对进一步理解团簇的物理化学性质有重要意义。本项目主要研究了1）发展了对支撑团簇具有原子分辨率的扫描隧道显微成像技术，进而首次在实空间中直接观测到金字塔构型的Au20团簇的原子结构并揭示其在表面上的熟化机制；2）研究了水分子团簇和水分子薄膜与石墨烯的相互作用，3）利用第一性原理研究了大尺寸硅团簇的结构和电子性质。此外，本项目中我们实现了表面上团簇尺寸的均一性制备，这对进一步研究特定尺寸团簇的非线性光学、等离激元、激发态等性质提供了可能性。