Structure and electronic properties of transition metal dichalcogenide MX2 (M = Mo, W, Nb; X = S, Se) monolayers with grain boundaries

• Atomistic structures of GBs in MX2 (M = Mo, W, Nb; X = S, Se) monolayer were identified.
• Stability of GBs in the MX2 (M = Mo, W, Nb; X = S, Se) monolayer were studied.
• Electronic properties of GBs in the MX2 (M = Mo, W, Nb; X = S, Se) monolayer were studied.
• Defect levels induced by the GBs are located within the band gap of semiconducting MX2.
• NbS2 and NbSe2 remain as metallic materials within grain boundaries.

Layered transition metal dichalcogenides with unique mechanical, electronic, optical, and chemical properties can be used for novel nanoelectronic and optoelectronic devices. Large-area monolayers synthesized using chemical vapor deposition are often polycrystals with many dislocations and grain boundaries (GBs). In the present paper, atomic structure and electronic properties of MX2 (M = Mo, W, Nb; X = S, Se) with the GBs were investigated using first principles based on density functional theory. Simulation results revealed that the zigzag-oriented GBs (which consist of pentagon/heptagons (5-7) pairs) were more stable than the armchair-oriented GBs (which consist of pentagon/heptagons (5-7-5-7) pairs). The GBs induced defect levels are located within the band gap for the semiconductor materials of MX2 (M = Mo, W; X = S, Se) monolayers, and the NbS2 and NbSe2 remained as metallic materials with GBs. Results provided a possible pathway to build these nano-layered materials into nanoelectronic devices.