Twisted and screw dislocation-driven growth of MoSe₂ nanostructures by chemical vapor transport

Twisted multilayers of two-dimensional materials attract widespread research interest due to their intriguing electronic and optical properties related to their chiral symmetry breaking and moiré effects. The two-dimensional transition metal dichalcogenide MoSe₂ is a particularly promising material for twisted multilayers, capable of sustaining moiré excitons. Here, we report on a rational bottom-up synthesis approach for twisted MoSe₂ flakes by chemical vapor transport (CVT). Screw dislocation-driven growth was forced by surface-fused SiO₂ nanoparticles on the substrates that serve as potential nucleation points in low supersaturation condition. Thus, crystal growth by in-situ CVT under addition of MoCl₅ leads to bulk 2H-MoSe₂ in a temperature gradient from 900 to 820 °C with a dwell time of 96 h. Hexagonally shaped 2H-MoSe₂ flakes were grown from 710 to 685 °C with a dwell time of 30 min on SiO₂@Al₂O₃(0001) substrates. Electron backscatter diffraction as well as electron microscopy reveals the screw dislocation-driven growth of triangular 3R-MoSe₂ with individual step heights between 0.9 and 2.9 nm on SiO₂@Si(100) under the same conditions. Finally, twisted MoSe₂ flakes exhibiting a twist angle of 19° with respect to the [010] zone axis could be synthesized.