Ions are protected on impact. Credit: Uni Innsbruck
When the ultracold droplets hit a hard surface, they behave like drops of water. Ions that were previously doped remain protected on impact.
The research group at the Department of Ion Physics and Applied Physics has been using the method of mass spectrometry for 15 years. Using a supersonic nozzle, tiny, superfluid helium can be produced with temperatures of less than one degree. They can be doped with atoms. In the case of ionized droplets, the particles of interest are attached to the charges, which are then measured in the mass spectrometer. The scientists stumbled upon an interesting phenomenon that has changed their work. "For us, this was a game-changing event," says Zappa. Everything at our lab is done with this method. The results of their studies have been published.
A surprising phenomenon.
When charged particles are fired at a metal plate, the particles are usually destroyed by the free electrons on the metal surface. They can't be measured in the mass spectrometer anymore. When the ion are packed in a helium droplet, they are protected from impact and can fly off with a few weakly bound helium atoms. Zappa says the ion are protected by the helium. He doesn't know the underlying mechanism. There is some evidence that the helium loses its superfluid property before impact and then behaves like a liquid, splashing away from the surface and only then partially evaporates. Another possibility is that the first droplets evaporate at the surface, forming a layer of gas that slows down subsequent droplets and protects them from evaporation. If one of these explanations is correct, further investigations will show other reasons. The scientists think that the method works with negative ion, which are normally very fragile.
The benefits of Nanotechnology.
This discovery improved the measurement method used by the team, as well as giving them important insights for other research groups that deal with the deposition of nanoparticles on surfaces. Metal nanoparticles are an example of this. Metal nanoparticles have very specific properties in modern technologies. The phenomenon now discovered in Innsbruck could be related to the fact that the generation of such films can be very inefficient.
Paul Martini and his team wrote a paper about splashing large helium droplets upon surface crashes. There is a DOI titled "10.103/PhysRevLett. 127.263401".
Journal information: Physical Review Letters.
The large heliumnanodroplets splash like water upon surface collisions was retrieved from thephys.org on December 28, 2021.
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