Helium droplets containing between 10³ and 10¹³ He atoms are formed via supersonic expansion of helium at stagnation pressures of 20 bar and temperatures between 6 K and 12 K into ultra-high vacuum. Evaporative cooling leads to a constant temperature of 0.37 K inside the He droplet, which represents an ideal environment for numerous investigations due to the fact that all vibrational and most of the rotational degrees of freedom are frozen out at these low temperatures. Electronically excited, positively or negatively charged helium atoms as well as electron bubbles are formed upon electron ionization. The interactions between these reactants and different dopants inside the helium droplets as well as on their surface are analyzed by means of high-resolution mass spectrometry.

Kontakt:
Univ.-Prof. Dr. Paul Scheier
E-Mail: Paul.Scheier@uibk.ac.at
Phone: +43 (0)512 507 52660

In the “ClusToF” experiment, ionic species can be studied via laser spectroscopy. It employs a novel method for the efficient formation of complexes between ions and helium atoms where highly-charged, doped helium nanodroplets are collided with a surface. By overlapping the resulting ion beam with a laser beam of variable wavelength, these complexes can be dissociated which is monitored in a time-of-flight mass spectrometer. The current scientific focus is on the search for carriers of the diffuse interstellar bands, a group of some 500 interstellar absorption features, of which so far only a few were successfully assigned to a carrier, the buckminsterfullerene cation C₆₀⁺. Furthermore, we are investigating the interaction between metal clusters and greenhouse gases to unravel the reaction mechanism at the molecular level, shedding light on their catalytic properties and potential applications in environmental mitigation strategies.

Contact:
Dr. Miriam Meyer
E-Mail: Miriam.Meyer@uibk.ac.at

Dr. Olga V. Lushchikova
E-Mail: olga.lushchikova@uibk.ac.at

Univ.-Prof. Dr. Paul Scheier
E-Mail: Paul.Scheier@uibk.ac.at
Phone: +43 (0)512 507 52660

Building on our recent report [F. Laimer et al Phys. Rev. Lett. 123, 165301 (2019)] on the production of stable, highly charged droplets of superfluid helium, a new experimental method [Tiefenthaler et al. Rev. Sci. Instrum. 91, 033315 (2020)] was designed to investigate chemical reactions in the sub-kelvin environment with a significantly higher ion yield compared to previous setups. We demonstrate a novel method of softly ionizing dopant molecules by proton transfer, while largely preventing fragmentation, even for notoriously delicate molecules. Recent measurements have unveiled promising insights into the role of various complexes and clusters in the reversible binding of H2 molecules, with implications for energy storage applications. Furthermore, the structure of metal clusters has been effectively elucidated through solvation in helium and subsequent observation of solvation shells. Presently, we are delving into the possibility of conducting collision-induced dissociation (CID) studies to accurately determine the binding energies of complexes formed by these metal clusters with greenhouse gases, thus serving as a representative model system for catalysts.

Contact:
Dr. Olga V. Lushchikova
E-Mail: olga.lushchikova@uibk.ac.at

As an extension to the setup Toffy1, we are assembling a new experiment to perform mass spectrometry and laser spectroscopy of fragile biomolecular ions embedded in helium nanodroplets (HNDs). HNDs are transparent from the deep UV to the far IR and serve as gentle matrices to provide a cryogenic environment, reducing the number of populated quantum states and freezing out structural fluctuations of the embedded biomolecules.

The new setup combines a HND source with a commercially available electrospray ionization (ESI) source and a time-of-flight-mass-spectrometer (TOF-MS). The ESI is used to softly ionize biomolecules and transfer them into the gas phase with minimum fragmentation. The extracted ions are then bent by 90° and merged with a traversing HND beam. The HNDs pick-up the ions, which are hereafter investigated by mass spectrometry and laser spectroscopy.

Contact:
Dr. Elisabeth Gruber
E-Mail: E.Gruber@uibk.ac.at

The Snowball experiment was designed to investigate the consequences of electron impact ionization on helium nanodroplets. Using two electrostatic deflector units, it is possible to separate the helium nanodroplets produced in the cluster source for their mass per charge ratio after ionization and therefore gather information on for example threshold appearance sizes of specific charge states for different polarities. Recently an oven and a deposition chamber that can be independently vented were added to the experimental setup. Using the ability to mass per charge select ionized, pristine helium nanodroplets, nanoparticles of various materials exhibiting a narrow size distribution can now be produced and deposited onto substrates for further analysis.

Contact:
Anna Maria Reider
E-Mail: Anna-Maria.Reider@uibk.ac.at

Univ.-Prof. Dr. Paul Scheier
E-Mail: Paul.Scheier@uibk.ac.at
Phone: +43 (0)512 507 52660

The Snowball experiment was designed to investigate the consequences of electron impact ionization on helium nanodroplets. Using two electrostatic deflector units, it is possible to separate the helium nanodroplets produced in the cluster source for their mass per charge ratio after ionization and therefore gather information on for example threshold appearance sizes of specific charge states for different polarities. Recently an oven and a deposition chamber that can be independently vented were added to the experimental setup. Using the ability to mass per charge select ionized, pristine helium nanodroplets, nanoparticles of various materials exhibiting a narrow size distribution can now be produced and deposited onto substrates for further analysis.

Contact:
Matthias Veternik
E-Mail: Matthias.Veternik@uibk.ac.at

Univ.-Prof. Dr. Paul Scheier
E-Mail: Paul.Scheier@uibk.ac.at
Phone: +43 (0)512 507 52660

Magnetron sputter deposition allows for the production of thin metallic films onto a wide range of substrate materials. The combination of different source materials, such as titanium or gold, with varying discharge voltages and working pressures of argon and nitrogen offers a large degree of control over the growth of the film, which can be monitored through an in-situ quartz crystal microbalance.

Since the properties of thin films do not only depend on their composition, as it is the case for bulk materials, but are also strongly governed by their microstructure and layer thickness, controlling their growth delivers a powerful tool to optimise their application in surface modification and nanotechnology. The resulting surface properties can include, among others, adaption of the roughness, absorptivity, reflectivity and electrical conductivity which can be investigated with atomic force microscopy (AFM), scanning tunneling microscopy (STM), absorption spectroscopy and a four-point-probe.

Univ.-Prof. Dr. Paul Scheier
E-Mail: Paul.Scheier@uibk.ac.at
Phone: +43 (0)512 507 52660