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Updated: Jul 8, 2025

Plasma-Assisted Molecular Beam Epitaxy Growth of Mg3N2 and Zn3N2 Thin Films
Published on: May 11, 2019
Oxygen Radicals Entrapped between MgO Nanocrystals: Formation, Spectroscopic Fingerprints, and Reactivity toward
Thomas Schwab1, Eva Muchová2, Korbinian Aicher1
1Department of Chemistry and Physics of Materials, Paris-Lodron University Salzburg, Jakob-Haringer-Straße 2a, Salzburg A-5020, Austria.
Abstract:
Compaction of dehydroxylated MgO nanocrystal powders produces adsorbed oxygen radicals with characteristic UV-vis spectroscopic fingerprints. Identical absorption bands arise upon UV excitation in an oxygen atmosphere but in the absence of uniaxial pressure. Photophysical calculations on MgO gas-phase clusters reveal that the observed optical transitions at 4.4 and 3.0 eV are consistent with adsorbed superoxide (O2·-) and ozonide (O3·-) species, respectively. The presence of these oxygen radicals is corroborated by electron paramagnetic resonance spectroscopy. Upon reaction with interfacial water, oxygen radicals convert into diamagnetic products with no absorptions in the UV-vis range. Since superoxide O2·- and ozonide anions O3·- play a key role in a variety of processes in heterogeneous catalysis, sensing, or as transient species in cold sintering, their UV-vis spectroscopic detection will enable in situ monitoring of transient oxygen radicals inside metal oxide powders.
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