Positrons Probing Matter: Applications of a Low-Energy High-Intensity Positron Beam

Colloquia
8 febbraio 2017
8 febbraio 2017

Positrons Probing Matter: Applications of a Low-Energy High-Intensity Positron Beam

Prof. Christoph Hugenschmidt
Physik Department E21 and FRM II, Technische Universität München, Germany

h 14:30
Venue: Polo Scientifico e Tecnologico Fabio Ferrari – Room A205
 

Abstract:
The neutron induced positron source NEPOMUC at FRM II provides the world’s highest intensity of 109 moderated positrons per second [1]. The high positron intensity leads not only to a drastically reduced measurement time and an improved signal-to-noise ratio but also to the realization of novel experiments using mono-energetic positrons. In solid state physics and surface science the positron is applied as a highly mobile nano-probe for the detection of vacancy-like defects and their chemical surrounding in a non-destructive way. For example, positron lifetime measurements are applied to identify different types of vacancies in thin perovskite layers [2]. Doppler broadening spectroscopy (DBS) using a scanning positron beam allows e.g. the imaging of the oxygen vacancy distribution in high-Tc superconductors [3]. Due to the elemental selectivity of the positron buried metallic layers and clusters can be investigated by so-called coincident DBS [4]. At the surface, the annihilation of low-energy positrons with core electrons initiates the emission of Auger-electrons primarily in the topmost atomic layer allowing the in situ observation of the surface segregation of Cu in Pd [5]. Within this contribution the basic properties of positron annihilation studies will be briefly explained and the benefit of positron beam experiments will be elucidated by selected experiments. In addition, an overview of the NEPOMUC beam facility and the positron instrumentation is given.

References:

[1] C. Hugenschmidt, C. Piochacz, M. Reiner, and K. Schreckenbach; New J. Phys., 14 (2012) 055027 [2] D.J. Keeble, R.A. Mackie, W. Egger, B. Löwe, P. Pikart, C. Hugenschmidt, and T.J. Jackson; Phys. Rev. B 81 (2010) 064102; D. J. Keeble, S. Wicklein, R. Dittmann, L. Ravelli, R. A. Mackie, and W. Egger; Phys. Rev. Lett. 105 (2010) 226102 [3] M. Reiner, A. Bauer, M. Leitner, T. Gigl, W. Anwand, M. Butterling, A. Wagner, P. Kudejova, C. Pfleiderer, and C. Hugenschmidt; Scientifc Reports, 6 (2016) 29109 [4] P. Pikart, C. Hugenschmidt, Y. Horisberger, M. Matsukawa, M. Hatakeyama, T. Toyama, and Y. Nagai; Phys. Rev. B 84 (2011) 014106 [5] J. Mayer, C. Hugenschmidt, and K. Schreckenbach; Phys. Rev. Lett. 05 (2010) 207401 Scientific Coordinator: Bruno Giacomazzo

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