Structural and Chemical Mechanisms Governing the Stability and Electronic Properties of Inorganic Janus Nanotubes

One-dimensional inorganic nanotubes hold promise for technological applications due to their distinct physical/chemical properties. Still, so far advancements have been hampered by difficulties in producing single-wall nanotubes with a well-defined radius. In this work, based on Density Functional Theory (DFT), we investigate the formation mechanism of different prototypes of inorganic nanotubes formed by the intrinsic self-rolling driving force found in asymmetric 2D Janus sheets. We show that for isovalent Janus sheets, the lattice mismatch between inner and outer atomic layers is the driving force behind the nanotube formation. At the same time, in the non-isovalent case, it is governed by the difference in chemical bond strength of the inner and outer layers leading to steric effects. From our pool of candidate structures, we have identified a handful of nanotubes with a preferred radius below 15 Å, which we hypothesize can display distinctive properties compared to their parent 2D monolayers. We investigate electronic properties and show that many of these nanotubes exhibit sizable band gaps and size-dependent electronic properties. Moreover, we observe that the flexoelectricity in these nanotubes is significantly larger than those of other nanotubes and their 2D counterparts. This work opens up an avenue of structure-property relationships of Janus nanotubes and demonstrates exciting new properties, which can accelerate the green transition to a more sustainable future.