January 21, 2025 Dataset Open Access

Data publication: Roadmap on Advanced/operando characterisation of solid state materials and devices for energy applications - Positron annihilation spectroscopy

Liedke, Maciej Oskar; Menéndez, Enric; Keeble, David J.; Čížek, Jakub

Positron annihilation spectroscopy (PAS) is a precise probe of point defects in bulk and nanomaterials, e.g., thin films. Positrons localize predominantly in the neutral and negatively charged open volume defects, i.e., vacancies and their agglomerations, extended defects, pores. The time to the inevitable annihilation of the positron with electron depends on the local electron density and scales proportionally with the open volume size. In insulators containing pores, Positronium (Ps) formation is enabled, so that the lifetime of the resulting ortho-Ps population again scales proportionally with pore size. Employing mono-energetic positron beams enables the study of near-surface buried defects. Positrons pre-accelerated to a given kinetic energy are implanted into solids following the so-called Makhov distribution [Fig. 1b]. Once localized in a defect, the positron lifespan increases and the overlap of the positron density with the core electron density is reduced. As a consequence, the Doppler shift of annihilation gamma rays becomes smaller. These characteristics are measured using two major techniques, namely positron annihilation lifetime spectroscopy (PALS) and coincidence Doppler broadening spectroscopy (cDBS or cDB-PAS), respectively. The analysis of the positron lifetime spectra [Fig. 2a] enables a decomposition into exponential components characterized by lifetime (ti) and intensity (Ii), which can be translated into defect type/size and concentration. Whereas the shape analysis of the broadened 511 keV annihilation spectrum provides insights to positron annihilation with low momentum valence electrons and high momentum core electrons. The latter determines the local chemical environment of positron annihilation sites (Fig. 2b), which is relevant for characterization of fusion materials. Here we present the research data for figures 1b, 2a, and 2b.