The growth study of bilayer and monolayer WSe2

The bilayer two-dimensional (2D) material design is indispensable to its future device applications. However, a controllable growth of bilayer 2D material still remains challenging. Here, we report a growth mechanism study of bilayer and monolayer WSe2 by a chemical vapor deposition (CVD) method. By tuning different growth parameters, we realized a bilayer growth on a monolayer WSe2 triangle domain, which was confirmed by optical microscopy, atom force microscopy, Raman scattering and photoluminescence characterizations. Our results reveal that original nucleation site for monolayer growth plays a key role to trigger a subsequent layer growth from the top surface of a monolayer domain. We have also found that a triangle domain was evolved from a hexagonal shape structure. It provides a general guideline for controllable growth of other 2D materials.