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.

Contact:
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:
Johannes Reichegger, MSc.
E-Mail: Johannes.Reichegger@uibk.ac.at

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

Messenger spectroscopy of C₆₀ derivatives - Searching for the carriers of the diffuse interstellar bands

Publication: Spectroscopy of helium-tagged molecular ions - Development of a novel experimental setup, Review of Scientific Instruments 94, 055105 (2023). DOI:10.1063/5.0144239

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

Spectroscopy of He-tagged photoactive (metal)organic molecules

Photoactive organic molecules are used in solar energy conversion systems, as photocatalysts and as photosensitizers in photodynamic therapy. The exact knowledge of the photophysical and photochemical properties of the underlying molecular complexes and the influence of the natural environment on them is therefore of great interest. A combination of mass spectrometry with laser spectroscopy, as well as isolation and embedding in a cryogenic environment, enables the determination of the geometry, electronic and photodynamic properties of these molecules in a well-defined environment. Our newly built experimental facility is used to study the electronic structure of (bio)molecules and how it changes by changing the environment, e.g. by adding single water molecules.

In the “Hydra” experiment set up in 2023, the focus lies on the deposition of clusters on surfaces. Charged helium nanodroplets are also used in this setup. By doping the droplets with metallic samples, clusters grow on the charges in the droplets. These doped droplets are then shot onto a surface, causing the helium to evaporate on impact. However, the majority of the clusters remain on the surface. By changing the experimental parameters (droplet size, charge state of the droplets, type of dopant, duration of the coating process), surface coatings with different biological, physical and chemical properties can be produced. The samples are analyzed using various microscopy methods such as AFM (Atomic Force Microscope), STM (Scanning Tunneling Microscope) or TEM (Transmission Electron Microscope).

Contact:
Thomas Pohl, MSc.
E-Mail:   Thomas.Pohl@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, MSc.
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.