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

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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.