Telluriding Monolayer MS₂ (M=Mo, W) via Sodium Scooter

The conversion of chalcogen atoms to other types in transition metal dichalcogenides has significant advantages for tuning bandgaps¹ and constructing in-plane heterojunctions²; however, difficulty arises from the conversion of sulfur or selenium to tellurium atoms owing to the low decomposition temperature of tellurides³. Here, we propose the use of sodium metal to deliver Te atoms for converting monolayer MoS₂ to MoTe₂ under a Te-rich vapor. Sodium metal easily anchors Te atoms and reduces the exchange barrier energy by scooting the Te atoms to replace the S atoms. The conversion was initiated at the edges and grain boundaries of monolayer MoS₂, followed by a complete conversion in the entire region. By controlling sodium concentration and reaction temperature of monolayer MoS₂, various phases such as semiconducting 2H-MoTe₂, metallic 1T'-MoTe₂, and 2H-MoS_2−xTe_x alloys were obtained with a wide range of electrical bandgap energies from 1.1–2.1 eV. This concept was further extended to WS₂. A high valley polarization of ~37% in circularly polarized photoluminescence was obtained in the monolayer WS_2−xTe_x alloy at room temperature.
Key words: Conversion, MoS₂, MoTe₂, Sodium scooter.