10-Jan-2020 - Albert-Ludwigs-Universität Freiburg

Nanobubbles in nanodroplets

Researchers investigate ultrafast reaction of superfluid helium triggerd by extreme ultraviolet laser pulses

A team headed by Professor Frank Stienkemeier at Freiburg’s Institute of Physics and Dr. Marcel Mudrich, professor at the University of Aarhus in Denmark, has observed the ultrafast reaction of nanodroplets of helium after excitation with extreme ultraviolet radiation (XUV) using a free-electron laser in real time.

Lasers generating high-intensity and ultra-short XUV and X-ray pulses give researchers new options for investigating the fundamental properties of matter in great detail. In many such experiments, material samples in the nanometer range are of particular interest. Some scientists use helium droplets no larger than a few nanometers as a means of transporting and studying embedded molecules and molecular nanostructures. Helium droplets are ideally suited for this purpose because they possess extraordinary properties. At an extremely low temperature of only 0.37 degrees above absolute zero, they move frictionlessly and are thus considered superfluids. Moreover, helium droplets usually are inert to the embedded molecules’ chemical processes and are completely transparent to infrared and visible light.

The team led by Stienkemeier and Mudrich wanted to find out how one of these superfluid droplets itself reacts when hit directly by an intense XUV laser pulse. The researchers used the world's first and only seeded free-electron laser FERMI in Trieste, Italy, which delivers high-intensity XUV pulses at a wavelength set by the team. Supported by model calculations, the researchers identified three elementary reaction steps: A very fast localization of electrons, the population of metastable states, and the formation of a bubble that eventually bursts at the surface of the droplets and ejects a single excited helium atom.

“For the first time, we have managed to directly follow these processes in superfluid helium, which take place in an extremely short time,” says Mudrich. “The results help to understand how nanoparticles interact with energetic radiation and then decay,” Stienkemeier adds. “This is essential information for the work aiming at directly imaging individual nanoparticles," he explains, “as it is being carried out at new intense radiation sources such as the European X-ray laser XFEL in Hamburg.”

Facts, background information, dossiers
  • nanodroplets
  • helium
  • free-electron lasers
More about Uni Freiburg
  • News

    Innocent and highly oxidizing

    Chemical oxidation, the selective removal of electrons from a substrate, represents one of the most important transformations in chemistry. However, most common oxidants often show disadvantages such as undesired side reactions. The chemist Marcel Schorpp and colleagues from the group of Pr ... more

    Programming with the Light Switch

    In the development of autonomous systems and materials, self-assembling molecular structures controlled by chemical reaction networks are increasingly important. However, there is a lack of simple external mechanisms that ensure that the components of these reaction networks can be activate ... more

    The origins of roughness

    Most natural and artificial surfaces are rough: metals and even glasses that appear smooth to the naked eye can look like jagged mountain ranges under the microscope. There is currently no uniform theory about the origin of this roughness despite it being observed on all scales, from the at ... more

  • Companies

    Albert-Ludwigs-Universität Freiburg

    more

More about Aarhus University
  • News

    How frogs' tongues become sticky

    Frogs' capture their prey with the sticky mucus covering their tongues, but this mucus isn't inherently adhesive. Frog mucus is thought to be pressure-sensitive, with tongue retraction strain triggering adhesion. A research team from Oregan State University, Aarhus University and Kiel Unive ... more

    Simpler and safer method for handling a useful but foul-smelling gas in chemical synthesis

    The chemical element sulfur is an important constituent in many pharmaceuticals and, consequently, it is desirable to be able to introduce sulfur-containing fragments efficiently in a broad range of chemical compounds. The Skrydstrup team provides an effective and safe way for introducing a ... more

    A patent-free playground

    Along with a number of leading Danish industrial companies, Aarhus University has opted out of the patent rat race in a new collaboration on industrially relevant basic research. Researchers and companies from all over Denmark publish all their results and data on the innovative Open Scienc ... more