Study of electronic structures of carbon and silicon clusters
In the last two decades the research on carbon and silicon has received a strong impulse since two discoveries have multiplied the perspectives of applications: - The existence of pure carbon molecules in the form of hollow cages with highly symmetric structure – fullerenes. - The luminescence of silicon particles. Both are results of experiments performed on particles, more precisely on atomic clusters. This dissertation is focused on studies of physical properties of size-selected carbon and silicon clusters. The research work is experimental - the electronic structure of small clusters has been investigated employing photoelectron spectroscopy. The results reached on carbon and silicon clusters can be summarised as follows: - For the first time, we suggest the existence of the fullerene at 20 carbon atoms on the basis of experimental results. As expected, it is not easy to achieve this fullerene. However, an opportune precursor can be synthesised whose fragmentation probably does not destroy the carbon cage structure. For the first time, the existence of the bowl isomer at 20 carbon atoms has been proved. The vibrational frequencies and the electron affinities of these two isomers have been measured and compared with those of the ring isomer. The experimental results are in line with theoretical predictions. - For negatively charged silicon clusters in the size range , the electronic structure does not show any band gap. We explain this as due to the occupation of surface states. The existence of excited states of different nature has been demonstrated. Their lifetimes have been found to vary in the range from few hundreds of fs to ns. The involved relaxation processes are supposed of at least three types. Furthermore, a new experimental method to investigate photofragmentation has been proposed. For the first time, pump-probe-type photoelectron spectroscopy has been used to study the fragmentation pattern.
Cluster, carbon, silicon, photoelectron spectroscopy, fullerene
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