Low-energy ion scattering set-up

Features

  • The ion source produces beams of H, He, Ne, and Ar ions with energies up to 20 keV.
  • The ionization chamber of the source can be filled to a typical pressure of 10-7 mbar.
  • The gas atoms are ionized by electrons emitted by a filament, and the positively charged ions can be subsequently accelerated to the desire energy.
  • Mass selection is carried out by magnetic deflection over an angle of 90°.
  • The size of the beam is adjusted by a set of slits.
  • The main (scattering) chamber is provided with 4 Knudsen-cells (K-cells) for molecular beam epitaxy (MBE) sample growth and with a precision 3-axes goniometer for the sample orientation.
  • The temperature of the sample mounted onto the goniometer can be varied in the range of 40 - 680 K.
  • Cooling is done by a closed-cycle He refrigerator, and heating by electron bombardment.
  • The main chamber is further equipped with a facility for low-energy electron diffraction (LEED), and three types of detectors.
    • One of them is a magnetic electron multiplier mounted at a fixed backward angle of 155° with respect to the incoming beam.
    • Two rotatable channel plate detectors cover the forward angle ranges from 35° to 55° and from 0° to 30°.
    • A surface barrier detector is mounted at a backward angle of 150° to measure Rutherford backscattering (RBS) spectra.
  • In addition, there is a preparation chamber which is equipped with an annealing and sputtering facility.
  • Annealing up to a temperature of 500 °C is possible.
  • The annealing oven is rotatable in order to change the angle between the sample surface and the sputtering beam from grazing to perpendicular incidence.
  • The base pressure of both chambers is 2×10-10 mbar.
  • The preparation chamber is connected to an oxygen oven and a nitriding oven for in situ oxidation and nitriding of the samples.
  • In the oxygen oven, samples can be oxidized in an O2 pressure up to 100 mbar, at a temperature of 20 - 800 °C.
  • The characteristics of the nitrogen oven will be presented in the near future.

See also

  • layout of the LEIS set-up
  • the 3-axes goniometer
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