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 as a function of diameter. Our calculations show that the electronic structure near the band gap is sensitive to the NT diameter: armchair MoS2 NTs act as indirect gap semiconductors for diameters up to approximately 5.0 nm, while armchair MoS2 NTs with larger diameters act as 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 is ascribed to the upward shift of the valence band peak at the point in small diameter NTs, which is caused by the tensile strain resulting from their tubular structures.