Structure and Electronic Properties of ${\mathrm{MoS}}_2$ Nanotubes

Structural and electronic properties as well as the stability of ${\mathrm{MoS}}_2$ nanotubes are studied using the density-functional-based tight-binding method. It is found that ${\mathrm{MoS}}_2$ zigzag ( $n,0\mathrm{}$) nanotubes exhibit a narrow direct band gap and ${\mathrm{MoS}}_2$ armchair ( $n,n$) possess a nonzero moderate direct gap. Interestingly, the ( $n,n$) tubes show a small indirect gap similar to the direct gap of ( $n,0\mathrm{}$) nanotubes. Simulated electron diffraction patterns confirm the existence of armchair and zigzag disulphide nanotubes. The structure of the ${\mathrm{MoS}}_2$ nanotube tips is explained by introducing topological defects which produce positive and negative curvature.