Low-energy systems – ToF-LEIS

ToF-LEIS makes use of low-energy ion beams enabling high-resolution analysis of composition and structure of the outermost atomic layers of a sample.

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.

Time-of-flight low-energy ion scattering (ToF-LEIS) is an analytical technique in surface physics that employs comparatively slow ions. 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. 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. In other words, with ToF-LEIS we can measure differences in chemical composition between individual atomic layers.

One vacuum system for preparation and analysis

Our unique ToF-LEIS system, originally transferred from Johannes Kepler University Linz in Austria in 2018, has been optimised for the preparation of clean sample surfaces. The ToF-LEIS beamline is complemented by a sample preparation and analysis chamber allowing for fabrication of materials, cleaning through ion bombardment, heating, exposure to different gases, and additional surface analysis. Analysis and modification are, thus, kept 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 contaminations. The system can, thus, aid to answer research questions from thin film technology, catalysis, and material transformations such as oxidation. You can find some recent ToF-LEIS studies from the Tandem Laboratory below.

  • 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.

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