Molecular Beam Epitaxy of Highly Crystalline MoSe 2 on Hexagonal Boron Nitride.

Molybdenum diselenide (MoSe ₂ ) is a promising two-dimensional material for next-generation electronics and optoelectronics. However, its application has been hindered by a lack of large-scale synthesis. Although chemical vapor deposition (CVD) using laboratory furnaces has been applied to grow two-dimensional (2D) MoSe ₂ cystals, no continuous film over macroscopically large area has been produced due to the lack of uniform control in these systems. Here, we investigate the molecular beam epitaxy (MBE) of 2D MoSe ₂ on hexagonal boron nitride (hBN) substrate, where highly crystalline MoSe ₂ film can be grown with electron mobility ∼15 cm ² /(V s). Scanning transmission electron microscopy (STEM) shows that MoSe ₂ grains grown at an optimum temperature of 500 °C are highly oriented and coalesced to form continuous film with predominantly mirror twin boundaries. Our work suggests that van der Waals epitaxy of 2D materials is tolerant of lattice mismatch but is facilitated by substrates with similar symmetry.