Atomic-Scale Edge Morphology, Stability, and Oxidation of Single-Layer 2H-TaS₂

Tantalum disulphide belongs to the group of transition metal dichalcogenides (TMDs) and has attracted attention for its unique structural, electronic, and catalytic properties. Herein, we report the edge properties of single-layer 2H-TaS₂ studied by using density functional theory calculations, because the knowledge of the edge morphology, stability, and surface energy is essential for the determination of nanoparticle shapes and understanding the nature of catalytically active sites. We calculate the grand canonical potential of TaS₂ clusters having various edge morphologies to evaluate the edge energies of the Ta-edge and S-edge terminated surfaces. Under S-rich conditions, the most likely shape of TaS₂ is a deformed hexagon dominated by the Ta-edge covered by S monomers, while the triangular shape is preferred under S-poor conditions. Exposed edges of the single-layer TaS₂ are susceptible to oxidation in air because both oxygen adsorption and substitution at the edge are strongly exothermic, -0.96 and -2.20 eV for single O atom, respectively. The XPS calculation shows that specific initial steps of oxidative process (adsorption, vacancy creation, substitution) are unlikely to be distinguished in the XPS spectra due to small shift of respective binding energies, but initial edge oxidation of TaS₂ should be observable by an asymmetry of the Ta 4f doublet towards higher binding energies.