Direct observation and <i>in-situ </i>control of interfaces between heterostructures of chemically and structurally distinct 2D materials

We show that when monolayer Bi₂Se₃ is CVD-grown on monolayer TMDs (MoS₂, MoSe₂, or WS₂), they prefer to grow either rotationally aligned with respect to the TMD crystal, or stabilize at certain specific angles. They form Moiré superlattices, which lead to dramatic changes in the optical and electronic properties, including the >99% quenching of the TMD’s bright photoluminescence (PL). When the heterostructure (HS) is exposed to a laser or an electron-beam treatment (LT or ET), the Bi₂Se₃ breaks into smaller domains and rotates into new Moiré patterns. It is possible to tunably increase and decrease the PL; visually change their color; and modify the population of neutral and charged excitonic species (A^- and A excitons), as well as their recombination energies with submicron spatial resolution. Thermal annealing reverses these changes and drives them back into stable Moiré configurations. We will also present in-situ observation of large (>100nm) Bi₂Se₃ domains rotating, splitting-up, and recombining, as well as improved (annealing) of the TMD crystallinity, using only perturbations from an SAED TEM electron-beam. Parallel first-principles electronic structure computations are presented on the resulting HSs in order to gain insight into the experimental observations.