Regensburg 2013 – scientific programme
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MI: Fachverband Mikrosonden
MI 9: Poster: Microanalysis and Microscopy
MI 9.11: Poster
Wednesday, March 13, 2013, 15:00–17:00, Poster B2
The Munich Scanning Positron Microscope — •Marcel Dickmann1, Werner Egger1, Christoph Hugenschmidt2,3, Gottfried Koegel1, Christian Piochacz2,3, Peter Sperr1, and Guenther Dollinger1 — 1Universität der Bundeswehr München, LRT2, Institut für Angewandte Physik und Messtechnik, D-85579 Neubiberg, Germany — 2Technische Universität München, Physik Department E21, D-85748 Garching, Germany — 3FRM II, Technische Universität München, D-85747 Garching, Germany
Positrons are very sensitive probes to analyse non-destructively small open volume defects, e.g. vacancies, vacancy clusters, and dislocations. From positron lifetime measurements defect-types and their concentrations can be determined. Conventional positron lifetime studies are of limited spatial resolution. Moreover, saturation trapping of positrons in defects may render a determination of concentrations impossible.
These disadvantages can be avoided using pulsed low-energy positron beams for lifetime measurements. By varying the beam energy, depth resolutions in the sub-µm-range can be obtained. These depth-profiles enable measurements of defect concentrations even at saturation trapping.
At our Institute a scanning positron microscope (SPM), which offers additional lateral resolution of ≥ 1 µm, has been developed. With this system defect distributions close to crack surfaces, created by monotonic fracture and in fatigue tests, have been successfully studied in pure Copper and in the alloy Al 6013. The main limitation in these studies was the low count-rate obtainable with conventional laboratory positron sources.
Currently, the SPM is transferred to the intense positron source (NEPOMUC) at the FRM II research reactor in Munich in order to increase the beam intensity by four orders of magnitude. This will open unique new possibilities for the investigation of defect structures in solids . In particular, more systematic investigations with higher spatial resolution of fatigued and fractured samples will be possible.