Oxidation process and designing Quantum-Confined Auride Platforms in 2D Dialkali-metal Monochalcogenide

In this work, we performed an ab initio study on the oxidation process of Na₂S and Na₂Se monolayers leading to the formation of Na₂O, with a special focus on stability and the evolution of their electronic structures throughout the process. We found that at each step of the transition, a Γ-Γ direct band-gap semiconductor behavior with good thermodynamic stability was maintained.

We also examined vacancy defects at different sites and the incorporation of gold atoms into them. Our results show that the presence of gold further stabilizes the monolayer and preferentially occupies chalcogen vacancies, clearly exhibiting an anionic character. This interesting result was corroborated through electrostatic potential maps and an analysis of Bader charges, where gold in Na2S, Na2Se, and Na2O gained 1.55 e, 1.57 e, and 0.97 e, respectively. Spin-orbit coupling generates a shift in the contributions of the Au-p orbitals to energies below the Fermi level, resulting in strongly localized bands, that reinforce this behavior. These results suggest that these materials are promising confined anionic platforms for future electronic and optoelectronic applications.

We thank DGAPA-UNAM projects IG101124, IA100226 and IN105026 for partial financial support. Calculations were performed in the DGTIC-UNAM Supercomputing Center projects LANCAD-UNAM-DGTIC-150, LANCAD-UNAM-DGTIC-368, and LANCAD-UNAM-DGTIC-422.