Stability and Electronic Structure of Double-Walled Transition Metal Dichalcogenide Nanotubes

The stability and electronic properties of double-walled MX2 nanotubes (M = Mo, W; X = S, Se, or Te) are investigated using density functional theory. It is shown that each of these double-walled transition metal dichalcogenide nanotubes exhibits metastable structures when the intertube distance is sufficiently small, relative to the corresponding 2D TMD monolayer. As the intertube interactions are dominated by van der Waals interactions, the extent of this metastability is primarily determined by the polarizability of the chalcogen. The band structure and band gaps of these structures show that the band gap of the material predominantly arises from inner-tube → inner-tube excitations between Mo/W states. Most interestingly, the band gap of the inner-tube was found to change significantly, by up to ∼0.3 eV, depending on the distance between the tubes, due to the radial compression caused by the outer-tube.