Speaker
Description
Positron annihilation spectroscopy (PAS) is a powerful, non-destructive method in modern materials science. Slow mono-energetic positron beams with variable energy enable depth-resolved characterization of atomistic open-volumes in solids. Positrons are highly sensitive to lattice defects, since they can be trapped at vacancies or vacancy clusters, resulting in a change of their lifetimes and a Doppler-broadening of the 511 keV annihilation line. These observables allow a quantitative identification of defect types and their concentrations. In polymers, positrons may form positronium. The analysis of positronium pick-off annihilation provides a quantitative determination of intrinsic free-volume sizes.
In this talk, we give an overview of PAS for material science, focusing on positron annihilation lifetime spectroscopy (PALS) and Doppler-broadening spectroscopy (DBS). We illustrate the methods with three examples: (a) radiation-damaged tungsten for future first-wall applications in fusion technologies, where PALS allows the detection of irradiation-induced vacancies [1]. (b) porous polymers and metal–organic frameworks (MOFs), where positron lifetimes correlate with pore sizes that influence diffusion and solubility of these materials [2]. (c) NV centers in diamond for quantum technologies, where nitrogen implantation and annealing at different temperatures affect the creation of various defect types in the diamond lattice. Furthermore, in-situ illumination with monochromatic light allows us to probe defect charge states. [3]
[1] M. Zibrov, et al. "Deuterium trapping by deformation-induced defects in tungsten." Nuclear Fusion 59.10 (2019): 106056.
[2] T. Stassin, et al. "Porosimetry for Thin Films of Metal–Organic Frameworks: A Comparison of Positron Annihilation Lifetime Spectroscopy and Adsorption‐Based Methods." Advanced materials 33.17 (2021): 2006993.
[3] M. Dickmann, et al. "Identification and Reversible Optical Switching of NV+ Centers in Diamond." Advanced Functional Materials (2025): 2500817.
