Twisted and screw dislocation-driven growth of MoSe ₂ 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 particular 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 <em>in</em>-<em>situ</em> CVT under addition of MoCl₅ leads to bulk 2H-MoSe₂ in a temperature gradient from 900&nbsp;°C to 820&nbsp;°C with a dwell time of 96&nbsp;h. Hexagonally shaped 2H-MoSe₂ flakes were grown from 710&nbsp;°C to 685&nbsp;°C with a dwell time of 30&nbsp;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&nbsp;nm and 2.9&nbsp;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.