The Art of Positronics in Contemporary Nanomaterials Science: A Case Study of Sub-Nanometer Scaled Glassy Arsenoselenides

Abstract

The possibilities surrounding positronics, a versatile noninvasive tool employing annihilating positrons to probe atomic-deficient sub-nanometric imperfections in a condensed matter, are analyzed in application to glassy arsenoselenides g-AsxSe100−x (0 < x < 65), subjected to dry and wet (in 0.5% PVP water solution) nanomilling. A preliminary analysis was performed within a modified two-state simple trapping model (STM), assuming slight contributions from bound positron–electron (Ps, positronium) states. Positron trapping in g-AsxSe100−x/PVP nanocomposites was modified by an enriched population of Ps-decay sites in PVP. This was proven within a three-state STM, assuming two additive inputs in an overall trapping arising from distinct positron and Ps-related states. Formalism of x3-x2-CDA (coupling decomposition algorithm), describing the conversion of Ps-decay sites into positron traps, was applied to identify volumetric nanostructurization in wet-milled g-As-Se, with respect to dry-milled ones. Under wet nanomilling, the Ps-decay sites stabilized in inter-particle triple junctions filled with PVP replaced positron traps in dry-milled substances, the latter corresponding to multi-atomic vacancies in mostly negative environments of Se atoms. With increased Se content, these traps were agglomerated due to an abundant amount of Se-Se bonds. Three-component lifetime spectra with nanostructurally- and compositionally-tuned Ps-decay inputs and average lifetimes serve as a basis to correctly understand the specific “rainbow” effects observed in the row from pelletized PVP to wet-milled, dry-milled, and unmilled samples.

Nanomilling-driven volumetric changes in multiparticulate As4S4-bearing nanocomposites recognized with a help of annihilating positrons

“…The highly heterogeneous multinanoparticulate substances obey selective localization of traps (Shantarovich and Goldanskii 1998), so that annihilation occurs through interconnected channels of positron trapping in vacancy-type volumetric defects (preferentially, negatively charged) and Ps-decaying in free-volume holes (preferentially, neutral). In case when Ps-decaying holes are the only sites which could be converted in positron traps (and vice versa), the volumetric effects in the substance under nanostructuralization obey generalized two-state simple trapping model (STM) modified for Ps-positron conversion known as x3-x2-CDA (coupling decomposition algorithm; see Shpotyuk et al 2015bShpotyuk et al , 2022. Within this model, the differential two-component PAL spectrum with well defined ( n ⋅I n ) and ( int ⋅I int ) inputs derived from unconstrained three-component PAL spectra of nanostructuralized (final) and unstructuralized (initial) substance is ascribed to hypothetical medium where conversion between trapping channels (positron trapping in vacancytype defects and Ps-decaying in free-volume holes) occurs in addition to annihilation from defect-free bulk states (see Shpotyuk et al 2015bShpotyuk et al , 2017aShpotyuk et al , b, 2018bShpotyuk et al , 2019bShpotyuk et al , 2020b.…”

“…The objective of current research is to identify subnm volumetric nanostructuralization effects in multiparticulate As 4 S 4 -bearing nanocomposites within quasiternary As 4 S 4 -ZnS-Fe 3 O 4 system in transitions between different hierarchical derivatives originated from parent anti-cancer-f luorescent-magnetic nanocomposite (1⋅As 4 S 4 /4⋅ZnS/1⋅Fe 3 O 4 ) prepared by nanomilling (Lukáčová Bujňáková et al 2020;Shpotyuk et al 2020c), employing positron annihilation lifetime (PAL) spectroscopy developed within the Positronics approach, serving as advanced instrumentation tool probing space-time continuum correlations for electrons annihilating with their anti-particles (the positrons) in nanostructuralized substance at extremely low sub-nm level, far below measuring possibilities available for conventional microstructural probes (Shpotyuk et al 2015b;2022).…”