Regensburg 2019 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 10: New Methods and Developments II: Scanning Probe, Spectroscopic, and Diffraction Techniques

O 10.10: Vortrag

Montag, 1. April 2019, 17:15–17:30, H3

Total Reflection High-Energy Positron Diffractometer at NEPOMUC — •Matthias Dodenhöft, Artur Elovskii, Sebastian Vohburger, and Christoph Hugenschmidt — Heinz Maier-Leibnitz Zentrum (MLZ) and Physik Department E21, Technische Universität München, 85748 Garching, Germany

Total Reflection High-Energy Positron Diffraction (TRHEPD) has been established as an ideal technique to determine the crystalline structure of topmost and immediate subsurface atomic layers. In contrast to Reflection High-Energy Electron Diffraction (RHEED), TRHEPD features an outstanding surface sensitivity, which stems from the repulsive crystal potential for positrons and the phenomenon of total reflection.
We have developed a new positron diffractometer that is coupled to the high-intensity positron source NEPOMUC (10⁹ moderated e⁺ per second) at the research reactor FRM II. The setup features UHV down to 10^-10mbar, sample temperatures up to 1000^∘C and a RHEED system for complementary measurements. The positron beam is accelerated and focused by an electrostatic lens system. We simulated the particle trajectories to optimize the beam properties in order to obtain a parallel, slightly converging beam with a small diameter of around 1mm. First experimental results are expected in spring 2019.
The project has been supported by the BMBF (funding number 05K16WO7).