Strain engineering of Janus transition metal dichalcogenide nanotubes: an ab initio study

We study the electromechanical response of Janus transition metal dichalcogenide (TMD) nanotubes from first principles. In particular, considering both armchair and zigzag variants of 18 select Janus TMD nanotubes that are identified as stable, we determine the change in bandgap and charge carriers' effective mass upon (tensile) axial and torsional deformations using density functional theory (DFT). We observe that metallic nanotubes remain unaffected, whereas the bandgap in semiconducting nanotubes decreases linearly and quadratically with axial and shear strains, respectively, leading to semiconductor- metal transitions. In addition, we find that there is a continuous decrease and increase in the effective mass of holes and electrons with strains, respectively, leading to n-type-p-type semiconductor transitions. We show that this behavior is a consequence of the rehybridization of orbitals, rather than charge transfer between the atoms. Overall, mechanical deformations form a powerful tool for tailoring the electronic response of semiconducting Janus TMD nanotubes.