Prof. Dr. Bernd von Issendorff
Physics Institute, University of Freiburg
gives a talk on the subject:
Matter at the nanoscale: study of the structure and dynamics of clusters
Clusters and nanoparticles often have properties rather different to those of the corresponding bulk material, which is due to their large surface-to-volume ratio and in general to quantum size effects, the discretization of otherwise continuous densities of states. Especially the latter makes them highly interesting candidates for the study of few to many particle physics. In my talk I will first explain the intricate interplay between electronic and geometric structure in simple metal clusters, which has been clarified by a combination of photoelectron spectroscopy on free, size-selected alkali and noble metal clusters and DFT-calculations. Then I will discuss that photoelectron spectra often not only yield information about the electronic density of states, but also about ultrafast relaxation processes happening between photon absorption and electron emission. I will illustrate such dynamics using recent results for a non-cluster system, anthracene anions. Here a strong photon energy dependence of the photoelectron spectra has been observed, which can be traced back to the influence of several autodetaching resonance of the anion. Finally, I will present results with respect to the nuclear dynamics of nanoparticles. Employing time-resolved x-ray diffraction, the evolution of strongly heated gas phase silver nanoparticle has been studied. A range of phenomena has been observed, from simple melting at lower heating strength to phase explosion at higher ones. Most interestingly, at intermediate heating strengths the transformation of the particles into of large silver bubbles has been seen, which can be traced back to a cavitation effect caused by the fast expansion following the abrupt heating. These experiments can be used to map the phase diagram of silver in a regime of rather larger temperatures and pressures.
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