NB: different date and room

Speaker:

Paul Scheier, Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Austria

Host:

Marcel Mudrich

Title:

Size selected Clusters and Nanoparticles from Doped Helium Nanodroplets

Abstract:

Pickup of atoms and molecules into superfluid He nanodroplets (HNDs) is a powerful technique to form clusters and nanoparticles at low (0.37 K) temperatures. The resulting dopant complexes are often analyzed utilizing mass spectrometry after electron ionization [1,2]. The typical log-normal size distribution of the neutral HNDs and the Poissonian pickup statistics lead to a substantial size spread of the dopant clusters. Very recently we were able to demonstrate that large HNDs can become very highly charged (more than thousand charges). At the same time, each collision with electrons leads to very little mass loss (either neutral He evaporation or highly asymmetric Coulomb explosion). Coulomb repulsion between charges of same polarity in highly-charged He droplets will lead to minimum energy configurations in the form of Coulomb crystals. Dopants are polarized and attracted by the charge centers, which thereby act as seeds for homogeneous cluster growth. Large metal nanoparticles grown in highly-charged HNDs are soft-landed onto surfaces and analyzed utilizing various high-resolution microscopy techniques and the resulting size distribution confirms a very uniform growth rate. Also small cluster ions of a specific size and composition can be formed inside multiply-charged HNDs with unprecedented efficiency. Several applications for cluster physics, ion spectroscopy and nanotechnology will be presented, supported by first results.

This work was supported by the EU commission, EFRE K-Regio FAENOMENAL EFRE 2016-4, the Austrian Science Fund FWF (P31149 and W1259) and the Swedish Research Council (contract No. 2016-06625)

References

[1]   J.P. Toennies, and A.F. Vilesov, Angew. Chem. Int. Ed. 43 (2004) 2622

[2]   A. Mauracher et al., Phys. Rep. 751 (2018) 1

Coffee/tea and cake from 15:00