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MI: Fachverband Mikrosonden

MI 9: Positron Annihilation Studies of Condensed Matter

MI 9.2: Vortrag

Mittwoch, 18. März 2015, 12:30–12:45, EMH 225

Characterization of High Purity Ni(100)-foils for Positron Moderation in a Novel Positron Microbeam Setup — •Thomas Gigl, Christian Piochacz, Markus Reiner, 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 at the Research Neutron Source FRM II provides the worlds most intense mono-energetic positron beam with an intensity of 10⁹ moderated e⁺/s. The CDB spectrometer at NEPOMUC enables depth dependent and spatially resolved defect studies by using conventional doppler broadening spectroscopy (DBS), and element-specific measurements with coincident DBS. In order to investigate the near-surface region and the bulk of a sample, the positron implantation energy can be increased to 30 keV. The lateral resolution amounts to 300 µm.

For the development of a positron beam with a diameter of <5 µm a Ni(100) foil with a thickness of 100 nm for positron re-moderation will be installed in transmission geometry in order to increase the beam brightness. In order to achieve a high yield of re-emitted moderated positrons, the Ni foil has to be annealed and surface contaminations such as carbon and oxygen have to be removed. For this purpose, temperature-dependent XPS measurements for characterizing the surface contaminations, and temperature-dependent DBS was performed to determine the annealing behaviour of the Ni foil. Financial support by BMBF (project no. 05K10WOB) is gratefully acknowledged.