Positron annihilation lifetime study of atomic imperfections in nanostructurized solids: On the parameterized trapping in wet-milled arsenic sulfides As4S4.

The phenomenon of positron-electron annihilation in lifetime measuring mode is considered as a tool to study nanostructurization in solids possessing mixed positron and positronium (Ps) trapping. Structural inhomogeneities due to guest nanoparticles in such solids are described in terms of substitution trapping in positron- and Ps-related sites within the same host matrix. The developed approach allows estimation of interfacial free-volume voids as being responsible for positron trapping and defect-free bulk positron lifetimes of nanoparticle-modified solids. For the example of arsenic sulfide, As₄S₄ nanoparticles embedded in polyvinylpyrrolidone (PVP) environment under high-energy ball milling, an alternative algorithm to parameterize these structural imperfections is justified. Interfacial free-volume voids between neighboring nanoparticles filled with loosely packed As₄S₄ crystallites are considered as the most probable positron trapping sites. The observed variations in mixed positron-Ps trapping modes under nanostructurization are adequately defined with respect to the chemistry of guest nanoparticles. Direct evidence for this algorithm is provided as the basis of experimental three-term decomposed positron lifetime spectra for As₄S₄-PVP nanocomposites parameterized with respect to different fitting protocols. [ABSTRACT FROM AUTHOR]