Dresden 2017 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 32: Microstructure and Phase Transformations - detection methods

MM 32.3: Vortrag

Dienstag, 21. März 2017, 12:15–12:30, IFW B

Positron-µm-beam for the Coincident Doppler Broadening Spectrometer at NEPOMUC — •Thomas Gigl, Marcel Dickmann, Markus Reiner, Benjamin Rienäcker, Matthias Thalmayr, and Christoph Hugenschmidt — Heinz Maier-Leibnitz Zentrum (MLZ) and Physik Department E21, Technische Universität München, Lichtenbergstr. 1, 85748 Garching, Germany

The positron beam facility NEPOMUC (Neutron induced Positron Source Munich) at the neutron source FRM II provides a mono-energetic positron beam with high intensity of 109 moderated positrons per second. A new CDB spectrometer was set into operation which enables defect studies by conventional Doppler broadening spectroscopy (DBS) and element-specific measurements with coincident DBS (CDBS) at the near surface and in the bulk of a sample with a positron implantation energy of up to 30 keV. According to first spatially resolved measurements the CDB Spectrometer provides a lateral resolution of 200 µm. With an additional 100 nm thin Ni(100) remoderation foil in transmission geometry a resolution of 50 µm could be measured. In order to achieve a high yield of re-emitted moderated positrons, the Ni foil has to be annealed and surface contaminations such as C and O have to be removed. For this purpose the foil was heated to about 400C in a H-atmosphere of about 10−3 mbar. After this procedure and cooling down to room temperature, the moderation efficiency of the Ni(100) foil could be measured to about 10%. Financial support by BMBF (project no. 05K10WOB) is gratefully acknowledged.

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