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O: Fachverband Oberflächenphysik

O 112: Development of Novel Methods I

O 112.1: Hauptvortrag

Donnerstag, 19. März 2020, 15:00–15:30, WIL C107

Positron Beams for Elemental and Structure Analysis of Surfaces — •Christoph Hugenschmidt — MLZ and Physics Department E21, Technische Universität München, Lichtenbergstraße 1, 85748 Garching, Germany

With the advent of bright low-energy positron beams novel analysis tools have been developed exploiting the unique properties of positron matter interaction such as repulsive crystal potential or positron trapping in surface states [1]. Positron annihilation is established for defect spectroscopy and the characterization of the free volume in amorphous matter. By applying a slow positron beam, however, defects near the surface can be specifically addressed, e.g. for the determination of the O vacancy concentration in YBa2Cu3O7-x [2]. The positron counterparts of reflection high-energy electron diffraction (RHEED) and electron induced Auger-electron spectroscopy (AES) intrinsically exhibit superior surface sensitivity. In contrast to electrons, positrons show total reflection for small glancing angles. It was demonstrated that with reflection high-energy positron diffraction the structure of the topmost and the immediate subsurface atomic layer of surfaces can be revealed with outstanding accuracy. The main advantages of positron annihilation induced AES are the missing secondary electron background and its topmost layer sensitivity for elemental analysis, e.g. for the in situ observation of the Ni adatom migration from the Pd surface into the bulk [3]. [1] C. H.; Surf. Sci. Reports 71 (2016) 547 [2] M. Reiner et. al.; Phys. Rev. B 97 (2018) 144503 [3] S. Zimnik et. al.; Surf. Sci. 664 (2017) 61