Studies of Size-Selected Semiconductor Clusters Using Negative Ion Photodetachment

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9521805 Neumark The aim of this research is to learn about how the properties of semiconductor clusters evolve over a large size range, spanning the molecular limit (10 atoms or less) up to the nanocrystalline regime (1000 atoms or more). The proposed experiments are specifically aimed at probing the electronic and vibrational spectroscopy of these clusters as a function of their size. The experiments will be conducted using two negative ion photodetachment techniques: photoelectron spectroscopy, for medium resolution (10 meV) survey work, and anion zero electron kinetic energy (ZEKE) spectroscopy for much higher resolution studies (0.2-0.3 meV). These techniques combine size-selectivity with reasonable spectral resolution and hence are ideal for spectroscopic studies of clusters over a wide size range. %%% The spectroscopy of size-selected clusters offers an unprecedented opportunity to understand how the properties of matter evolve from the molecular to the bulk limits. This type of work is appealing from the perspective of fundamental chemistry and physics, since we can learn how the molecular orbitals and vibrational frequencies of small molecules evolve into the electronic bands and phonons in extended crystalline structures. From a more applied point-of-view, small clusters have been implicated in the problems that arise in the plasma processing of semiconductors, and larger semiconductor clusters are beginning to show promise for use in electronic devices. Further characterization of the energetics and structure of the species involved in these applications is therefore highly desirable. This proposal is specifically aimed at mapping out the electronic and vibrational spectroscopy of semiconductor clusters over a wide size range, from less than 10 to more than 1000 atoms. To conduct this work, one requires experiments which combine size-selectivity with reasonable spectral resolution. This will be accomplished using two negative ion photodetachmen t techniques: photoelectron spectroscopy and, for higher resolution work, anion zero electron kinetic energy spectroscopy.