Controllable Epitaxial Growth of MoSe₂ Bilayers with Different Stacking Orders by Reverse-Flow Chemical Vapor Deposition

The stacking order plays a critical role in the electronic and optical properties of two-dimensional materials. It is however of great challenge to achieve large-size and homogeneous bilayer crystals with precisely controlled stacking orders. Here, we demonstrate an optimized chemical vapor deposition strategy to grow MoSe2 bilayers with controlled AA or AB stacking sequences. Reverse gas flow effectively suppresses the random nucleation centers, leading to uniform growth of the second layer of MoSe2 on the first monolayer. A customized temperature profile selectively activates the growth of the MoSe2 bilayer with different stacking orders: the AA stacking MoSe2 bilayer tends to form at 810 °C, and the AB stacking MoSe2 bilayer prefers to grow at a higher temperature of 860 °C. A series of characterization methods confirm that MoSe2 bilayers with different stacking orders exhibit distinct crystal structures and physical properties. Our results demonstrate a robust and effective route for the controllable synthesis of transition metal dichalcogenide bilayers, which will benefit the development of two-dimensional materials and van der Waals heterostructures.