Indirect-to-direct band gap crossover of single walled MoS2 nanotubes

Abstract

Using density functional theory, the electronic structures of single walled molybdenum disulfide nanotubes (MoS2 NTs) were investigated. The armchair MoS2 NTs are indirect gap semiconductors for diameters up to approximately 5.2 nm, while those with larger diameters are direct gap semiconductors with band edges located in the vicinity of k = 2π/3. This finding implies that MoS2 NTs with large diameters should exhibit similar photoluminescence to 2D monolayer MoS2 sheets. This indirect-to-direct band gap crossover accounts for the relative upward shift of the valence band peak at the Γ point in small diameter NTs, owing to the tensile strain arising from curvature.