Positron Spectroscopy Techniques at Marmara University:
Defect (Free Volume) Characterization of Materials as Technological Application



Marmara University, Faculty of Arts and Science, Physics Department, 34722 Göztepe, Istanbul, TURKEY

E-mail: uyahsi@marmara.edu.tr

We introduce work done at Marmara Positron/Positronium Laboratory (MARPOS) using the measurement techniques of Positron Annihilation Lifetime Spectroscopy (PALS) based on fast-fast coincidence spectroscopy and Doppler Broadened Emission Spectroscopy (DBES). We also introduce a variable energy positron beam system using the DBES technique for surface depth profile of vacancy defects (or free volume) of films and coatings.

Vacancy Defects in materials are open free spaces (significantly small diameter of 0.1-1 nm) inside a molecule or crystal. Defect hunting is then an essential asset for the materials workers. Positron techniques eventually play an important role in determining the defect configuration in materials to relate to the material’s macroscopic properties [1].

The PALS technique measures the time difference between 1274 keV prompt gamma and 511 keV annihilation gamma. We mainly measure the ortho-positronium (o-Ps) lifetime and intensity as a measure of free volume (vacancy) hole size and free volume. The DBES technique relies on the measurement of the Doppler broadening of the emitted annihilation gamma, giving information about the electron momentum distributions of the molecules in the environment. The area under the 511 keV gamma spectrum is separated into low and high momentum regions. Thus, we extract two parameters as S and W, respectively: the first is vacancy related, and the second is chemical-related [2].

We will discuss some applications recently worked at MARPOS: ionic conductivity of PVdF-co-HFP/LiClO4 [2], the role of defects on structural properties of Mg/B co-doped ZnO nanoparticles, effects of sintering and zircon mullite doping on nanostructural vacancies of bovine hydroxyapatite, etc.

[1] Y. C. Jean, et al., Principles and Applications of Positron & Positronium Chemistry, World Scientific Pub. Co., New Jersey, USA.;  Z. Yu, U. Yahsi, et.al., J. Polym. Sci. B: Polym. Phy., 32, 2637 (1994).

[2] Ionic Conductivity of PVdF-co-HFP with LiClO4: Free Volume Effects Probing by PALS”, U. Yahsi, H. Deligöz, et. al, Radiation Effects and Defects in Solids, 174(3), 214-228 (2019).