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

News

Successful ErUM-Pro proposals

Research with positrons

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.