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85748 Garching

CDBS

Coincident Doppler-broadening spectrometer

The Coincident Doppler-broadening spectrometer (CDBS) at NEPOMUC allows the detection of open volume defects and their chemical surrounding. Defect distributions can be imaged in 3D by lateral scanning with the energy variable positron beam.

The Doppler broadening of the 511 keV annihilation line contains information of the electron momentum distribution at the positron annihilation site in the sample. Since the probability of core electron annihilation decreases in open-volume defects a narrowing of the annihilation line is observed. For this reason, Doppler broadening spectroscopy (DBS) is particularly suited to detect lattice defects in a sample. DBS with the monoenergetic positron beam allows the analysis of defect profiles, energy dependent 2D imaging of defects, and defect annealing as a function of temperature. In addition, CDBS is applied in order to gain elemental information about the positron annihilation site and hence about the chemical surrounding of defects.

Technical Data
Beam properties
  • Positron implantation energy: E = 0.2 – 30 keV
  • Mean positron implantation depth: up to several µm (material dependent)
  • Beam size: adjustable between 0.03 – 3 mm Ø
2D x-y-scans
  • Scan area: 20 × 20 mm2
  • Step size adjustable between 0.1 and 10 mm
High-purity Ge detectors
  • 30 – 35% efficiency
  • Energy resolution: 1.4 keV at 477.6 keV
Sample
  • Size
    • optimal size: 6 × 6 mm2, thickness: 0.1 – 1 mm
    • in general: 0.5 × 0.5 × 0.01 mm3 – 20 × 20 × 3 mm3
  • Optimum 4 samples on one sample holder:
    • < 10 × 10 mm2
  • Temperature: 100 K – 900 K
Typical measurement times
  • DBS: ~ 1 – 2 min/ spectrum
  • DBS: ~ 8 h full 2D overview scan (with Δx = Δy = 1 mm)
  • DBS: ~ 1 h depth profile (t = 2 min, 30 energy values)
  • CDBS: ~ 4 – 6 h/ spectrum

Instrument Scientist

Prof. Dr. Christoph Hugenschmidt
Phone: +49 (0)89 289-14609
E-Mail: christoph.hugenschmidt@frm2.tum.de

CDBS
Phone: +49 (0)89 289-14774

TUM Research Group:
Physics with Positrons

Operated by

TUM

News

Research with positrons

Research with positrons

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Citation of the instrument

Heinz Maier-Leibnitz Zentrum. (2015). CDBS: Coincident Doppler-broadening spectrometer. Journal of large-scale research facilities, 1, A23. http://dx.doi.org/10.17815/jlsrf-1-50

For citation please always include the DOI.

Gallery

CDBS
CDBS
© W. Schürmann, TUM
2D defect map
2D defect map

2D defect map of an plastically deformed Al sample (below) and optical image (above).

Elemental signature of layered samples
Elemental signature of layered samples

Thin Sn layers of various thickness buried in an Al matrix: Ratio curves recorded with CDBS reveal the elemental signature of layered samples.

MLZ is a cooperation between:

Technische Universität München> Technische Universität MünchenHelmholtz-Zentrum Hereon> Helmholtz-Zentrum Hereon
Forschungszentrum Jülich> Forschungszentrum Jülich

MLZ is a member of:

LENS> LENSERF-AISBL> ERF-AISBL

MLZ on social media: