Large-scale interlayer rotations and Te grain boundaries in (Bi,Sb)2Te3 thin films

We report the observation of two distinct large-scale defects in (Bi,Sb)2Te3 topological insulator (TI) thin films grown by molecular beam epitaxy. Small-angle rotations are detected between quintuple layers of the TI film, extending throughout a grain and beyond, and nm-sized Te formations are discovered that extend along grain boundaries. Density functional theory calculations suggest that the rotational defects can affect the local band structure of the film while preserving spin-momentum locking in the Dirac bands, and that the Te nanostructures at grain boundaries can result in wider-band-gap regions between the grains.