Low-energy systems – ToF-LEIS

Woman working on the LEIS system. Two chambers made from steel and covered with aluminium foil are visible. On the top of the chambers there are several measurement instruments as well as instruments for moving samples.

ToF-LEIS makes use of low-energy ion beams. This enables high-resolution measurement of a material’s composition and structure close to the surface.

Time-of-flight low-energy ion scattering (ToF-LEIS) is an analytical technique in surface physics that employs comparatively slow ions. In the Tandem Laboratory set-up, these ions are produced from gases such as helium or neon with energies below 10 keV. This can be compared with the large Tandem accelerator, which accelerates ions up to 50 MeV.

At lower velocities, the ions are unable to penetrate deeply into the material but are instead scattered after colliding with the outermost atomic layers.

The reduced velocity means that the ions interact more strongly with the sample surface, providing more detailed information about it compared with higher-energy ions that pass through it. Consequently, it is possible to analyse the chemical composition of these surface layers with a depth resolution down to one ångström (1 Å) – that is, the size of a single atom.

A unique ToF-LEIS set-up

The ToF-LEIS system, originally transferred in 2018 from Johannes Kepler University Linz in Austria to the Tandem Laboratory, is unique and has been optimised for the preparation of clean samples. In the sample chamber, materials can be fabricated, cleaned through ion bombardment, heated, and exposed to different gases. At the same time, they can also be analysed – all within the same sealed ultra-high vacuum system.

Studying effects at or near the surface

The ToF-LEIS set-up is particularly well suited for studying processes at or close to material surfaces, such as diffusion, adsorption, or surface contamination. The system can also be applied to research questions in thin film technology, catalysis, and material transformations such as oxidation.


Recent ToF-LEIS studies at the Tandem Laboratory include the formation of different crystalline structures in ultrathin nickel silicide films, relevant for contact layers in modern electronics. Another example is surface segregation and diffusion of components in EUROFER97 steel, which is planned for use in future fusion power plants.

  • Gas ion source allowing for easy switching between different gases. Commonly employed ion beams include H, He and Ne.
  • Ion energies between 0.5 and 10 keV.
  • Electrostatic chopping of the ion beam proving the basis for time-of-flight measurements.
  • Detection of backscattered particles under a scattering angle of 129°.
  • Separation of charged from neutral scattered particles possible allowing to access information from different layers of the sample.
  • Annealing of the sample at up 900°C.
  • Base pressure: 2 x 10-10 mbar.

  • 3-cell evaporator (Omicron model EFM 3T) allowing for in-situ sample growth of up to 3 materials simultaneously.
  • Sputter gun with ion energies of 5 keV and currents of a few nA.
  • Annealing of the sample at up to 1000°C.
  • Auger electron spectroscopy set-up (PHI model 10-155).
  • Low-energy electron diffraction set-up (ErLEED 3000 SPECS GmbH).
  • Ultrahigh vacuum with base pressure of 4 x 10-10 mbar.
  • Gas exposure of the sample possible.

Contact

Last modified:

FOLLOW UPPSALA UNIVERSITY ON

Uppsala University on Facebook
Uppsala University on Instagram
Uppsala University on Youtube
Uppsala University on Linkedin