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ETH Zrich - D-PHYS - Solid State Physics - Microstructure Research - Instrumentation - SEMPA

SEMPA

Selected Article

Nat. Comm 7, 13611 (2016)
Critical exponents and scaling invariance in the absence of a critical point
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Proc. R. Soc. A 472, 2195 (2016)
Thirty per cent contrast in secondary-electron imaging by scanning field-emission microscopy
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Phys. Rev. B 89, 014429 (2014)
Domain-wall free energy in Heisenberg ferromagnets
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Phys. Rev. B 87, 115436 (2013)
Scale invariance of a diodelike tunnel junction
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Scanning Electron Microscopy with Polarisation Analysis Of The Secondary Electrons (SEMPA)
SEMPA is a technique first introduced by Koike et al in 1984. It images the magnetization vector by measuring the spin polarization of secondary electrons emitted in a scanning electron microscope (SEM). Our instrument is based on a Hitachi 4100S UHV-SEM with a field emission cathode that produces a highly focused electron beam. The factory specified resolution of the microscope is 2nm. In the geometry used for SEMPA operation, we can achieve a lateral resolution better than 10nm. The spin polarization of the secondary electrons emitted from the sample surface is measured with a modified high voltage Mott detector. The detector is equipped with 4 counters and measures simultaneusly one in-plane- and the perpendicular component of the electron spin polarization vector. Apart from the superior resolution with respect to other imaging techniques such as scanning KERR microscopy (SKEM), the SEMPA is able to measure an absolute magnetic signal - the electron spin polarization (P) - whereas the Kerr effect measures a reflectivity difference for two directions of the magnetization.
The SEMPA instrument with the preparation chamber on the right hand side and the SEM chamber on the left.

Normal base pressures are in the range of 4*10-11mbar and 8*10-11mbar. The 60kV Mott detector with it's pink ceramic insulator is clearly visible on the left.
The SEMPA preparation chamber is equipped with a variety of sample preparation and characterization tools:
  • Auger analyzer (CMA) for chemical characterization of the sample surface

  • Low energy electron diffraction optics (LEED) for structural characterization

  • Ion sputtering gun

  • High temperature heating stage (2500C)

  • Evaporators for epitaxial growth of metal thin films

  • Evaporation stage with a special arrangement of apertures for growing laterally structured thin films.
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