Cavity ring-down spectroscopy on size-selected, supported clusters

本项目旨在利用消逝波腔衰荡光谱技术，在1.7 eV到6.0 eV的光子能量范围内对尺寸选择的金属和半导体团簇进行光谱研究，以研究氧化物表面上尺寸选择的金属和半导体团簇的电子结构和光学性质。氧化物是理想的载体材料，因为团簇的重要光学跃迁位于它们的带隙内。在这些研究中，将开发和优化EW-CRDS，这是一种超灵敏的表面光谱，用于在超高真空条件和低温下研究大小选择的、被支撑的团簇。将考虑两种实验方案：a)单片折叠谐振器和b)微型立方体光学谐振器。在这两种情况下，星团都将沉积在两个光学装置的全内反射平面上，并将通过吸收相关的逝去波由CRD进行光谱探测。这两个腔都具有与偏振无关的精细技术，允许研究偏振相关的现象。这一实验方案将在本计划的第一学期用于研究沉积的单一尺寸的金属团簇的光吸收，以便调查这些铸币金属团簇的电子结构的差异，并通过分析偏振相关的吸收来获得它们的形态和结构信息。这些团簇将被直接沉积到光学器件的SiO_2表面上，或者沉积到生长在谐振器的无定形SiO_2表面上的薄的氧化镁和二氧化钛薄膜上。

This project aims at the spectroscopic study of size-selected, supported clusters in the photon energy range from 1.7 eV to 6.0 eV by means of the evanescent wave cavity ring-down spectroscopy in order to study the electronic structure and optical properties of size-selected metal and semiconductor clusters supported on oxide surfaces. Oxides are ideal support materials as important optical transitions of clusters lie energetically within their band gaps. For these studies the EW-CRDS, an ultrasensitive surface spectroscopy, will be developed and optimized for studying size-selected, supported clusters under UHV conditions and at cryogenic temperatures. Two experimental schemes will be considered: a) monolithic folded resonators and b) miniature cubical optical resonators. In both cases the clusters will be deposited onto the planes of total internal reflection of the two optical devices and will be probed spectroscopically by CRD through adsorption of the associated evanescent waves. Both cavities have a polarization-independent finesse, allowing polarization-dependent phenomena to be studied. This experimental scheme will be used in the first term of this program to study optical absorptions of deposited, metal clusters of a single size in order to investigate differences in the electronic structure of these coinage metal clusters and to obtain information of their morphology and structure by analyzing polarization-dependent absorptions. The clusters will either be deposited directly onto the SiO2 surface of the optical devices or onto thin MgO and TiO2 films grown onto the amorphous silica surface of the resonators.