Designing quantum-confined auride platforms in 2D dialkali-metal monochalcogenides

In this manuscript, we present a computational study based on density functional theory to investigate the stepwise oxidation of two-dimensional Na 2 S and Na 2 Se compounds to form Na 2 O. Our results show that both the pristine and the intermediate oxidized monolayers exhibit direct semiconducting behavior. The intermediate and the fully oxidized structures are thermally and thermodynamically stable up to room temperature. While vacancy formation in the pristine monolayers is energetically costly, gold incorporation in these vacancies stabilizes the monolayers. The most stable system is when gold occupies an O vacancy site; in such a location, it exhibits a clear anionic character, as demonstrated by Bader charge analysis and electrostatic potential mapping. Gold in Na 2 S, Na 2 Se, and Na 2 O gains 1.55 e, 1.57 e, and 0.97 e, respectively. Spin-orbit coupling stabilizes this behavior by shifting the contributions of the Au-p orbitals towards negative energies, resulting in highly localized bands. The local environment modulates this effect. Our findings establish dialkali-metal monochalcogenide monolayers as a promising tunable environment for embedding charge-active impurities, with potential applications in low-dimensional charge transport, defect engineering, and quantum electronics.