Positrons in Material Sciences: Intense Beams for Defect Studies and Applications

The Helmholtz-Center Dresden-Rossendorf operates several user beamlines for materials research using positron annihilation energy and lifetime spectroscopy. The superconducting electron LINAC ELBE [2] drives a hard X-ray source, which generates positrons through pair production. The high-intensity Mono-energetic Positron Source MePS utilizes moderated positrons with adjustable kinetic energies ranging from 500 eV to 16 keV for depth profiling of defects in thin films. A magnetic beam transport system consisting of a beam chopper, a beam buncher, and a post-accelerator guides the positron beam towards the sample under investigation. Fully digital data processing of positron annihilation lifetime events generates high-quality spectra with timing resolutions down to about 210 ps and count rates in excess of 120 kcps.
The MePS facility is currently complemented by an additional beamline named Apparatus for In-situ Defect Analysis, AIDA-II, where in-situ defect studies are to be performed in a wide temperature range during thin film growth and under ion irradiation. A complimentary but functionally similar setup, AIDA-I, is operated at a 22Na-based mono-energetic continuous positron beam used for in-situ (coincidence) Doppler-broadening positron annihilation spectroscopy experiments. Recent developments figuring the formation and time dynamics of hydrogen-induced vacancies in nickel and niobium and the role of defects in magneto-ionics and ZnO semiconductor films will be presented.
The MePS facility has partly been funded by the Federal Ministry of Education and Research (BMBF) with the grant PosiAnalyse (05K2013). The initial AIDA system was funded by the Impulse- und Networking fund of the Helmholtz-Association (FKZ VH-VI-442 Memriox). The AIDA facility was funded through the Helmholtz Energy Materials Characterization Platform.