Journal of large-scale research facilities, 1, A23 (2015) http://dx.doi.org/10.17815/jlsrf-1-50

Published: 19.08.2015

CDBS: Coincident Doppler-broadening spectro-
meter

Heinz Maier-Leibnitz Zentrum
Technische Universität München

Instrument Scientists:
- Christoph Hugenschmidt, Heinz Maier-Leibnitz Zentrum (MLZ), Technische Universität München,

Garching, Germany, phone: +49.(0)89.289.14609, email: christoph.hugenschmidt@frm2.tum.de

Abstract: The CDBS, operated by the Technische Universität München, located at NEPOMUC, allows
the detection of open volume defects and their chemical surrounding. Defect distributions can be im-
aged in 3D by lateral scanning with the energy variable positron beam.

1 Introduction

The Doppler broadening of the 511 keV annihilation line contains information of the electron momen-
tum 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, Dopple broadening spectroscopy (DBS) is particularly suited to detect lattice defects in a
sample. DBS with the monoenergetic positron beam allows the analysis of defect pro�les, energy de-
pendent 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.

2 Technical Data

2.1 Beam properties

• Positron implantation energy: E = 0.2 – 30 keV
• Mean positron implantation depth: up to several µm (material dependent)
• Beam size: adjustable between 0.3 – 3 mm Ø

1

http://jlsrf.org/
http://dx.doi.org/10.17815/jlsrf-1-50
https://creativecommons.org/licenses/by/4.0/


Journal of large-scale research facilities, 1, A23 (2015) http://dx.doi.org/10.17815/jlsrf-1-50

Figure 1: Instrument CDBS at NEPOMUC (Copyright by W. Schürmann, TUM).

2.2 2D x-y-scans

• Scan area: 20 x 20 mm2
• Step size adjustable between 0.1 and 10 mm

2.3 High-purity Ge detectors

• 30 % e�ciency
• Energy resolution: 1.4 keV at 477.6 keV

2.4 Sample

• Size
optimal size: 6 x 6 mm2, thickness: 0.1 – 1 mm
in general: 0.5 x 0.5 x 0.01 mm3 – 20 x 20 x 3 mm3

• Optimum 4 samples on one sample holder: < 10 x 10 mm2
• Temperature: 100 K – 900 K

2.5 Typical measurement times

• DBS: ∼ 1 – 2 min / spectrum
• DBS: ∼ 8 h full 2D overview scan (with ∆x = ∆y = 1 mm)
• DBS: ∼ 1 h depth pro�le (t = 2 min, 30 energy values)
• CDBS: ∼ 4 – 6 h / spectrum

2

http://dx.doi.org/10.17815/jlsrf-1-50
https://creativecommons.org/licenses/by/4.0/

	Introduction
	Technical Data
	Beam properties
	2D x-y-scans
	High-purity Ge detectors
	Sample
	Typical measurement times