Band structure of MoSTe Janus nanotubes

Nanotubes generated by rolling up transition metal dichalcogenide Janus monolayers are a new class of low-dimensional materials, which are expected to display unique electronic properties compared to their parent two- and three-dimensional structures. Here, we investigate the band structure of $1H$-MoSTe Janus armchair and zigzag nanotubes, which were recently hypothesized to be stable as single-walled structures with radii of only a few nanometers. We first investigate the most stable nanotube sizes and assess the influence of quantum confinement and curvature on the band structures, showing that these are heavily modified by curvature while confinement effects are negligible. The curvature dependence is then further studied by analyzing the band gap dependence on the nanotube radius, where band gap changes as large as 0.5 eV are observed. By investigating the band edge positions and orbital projected density of states for different tube sizes, we find that this high sensitivity is mainly attributed to the Mo $d$ states in the conduction band.