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A Flexible Method for Production of Stable Atomic Clusters with Variable Size for Chemical and Catalytic Activity Studies
Final rept. 23 Jul 2009-31 Oct 2011
DELFT UNIV OF TECHNOLOGY (NETHERLANDS)
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The goal was to set up a flexible source for production of atomic clusters with large production rate and to measure their superconducting transition temperature. We have set up a generator based on spark discharge electrode ablation and size selected the produced clusters by mobility classification. The size distributions were measured on samples of gallium and platinum atomic clusters. Total spark energy was found to have some effect on the particle size distribution, and the inlet gas temperature has a large effect. The size distributions clearly exhibit nonscalability expected for small clusters, showing distinct peaks in the case of Pt, which we attribute to magic numbers, i.e. sizes of high stability. We also designed and set up an experiment using aerosol photoemission under variable temperature to observe the superconducting transition temperature. Unfortunately we were unable to observe the expected discontinuity due to the superconductivity transition for any chosen size due to the limitations of our experimental setup, namely the signal-to-noise ratio. Another problem may have been the a lack of clusters of the targeted size, for which the highest transition temperature is predicted, as it does not correspond to a magic number and the less stable sizes were likely etched away by oxidizing impurities. Both problems appear solvable for future research. Thus up to date, we were neither able to prove nor to disprove the predictions of Kresin et al regarding superconductivity of atomic clusters. Summarizing, we can say that a large step has been taken with respect to production of small n100 atomic clusters. Efficient charging by photoemission could be applied for efficient size separation of virtually any material and any size of atomic clusters in the future. The mass production rate of 1 gday is within reach. This is of great interest for applications such as catalysis and superconductivity.
APPROVED FOR PUBLIC RELEASE