Fig. 4: Mechanism of facet-selective epitaxial growth.

a Interfacial structural models of epitaxial CsPbI3 crystals with (002) out-of-plane facet on monolayer WSe2 at possible orientation angles. b The calculated formation energy of epitaxial CsPbI3 per unit cell volume with different facets on monolayer WSe2 at possible orientation angles. The symbols represent the calculated formation energy at a given facet and orientation of the epilayer. The solid line represents the energy barrier between different epitaxial orientations. c A representative optical image of epitaxial multiple CsPbI3 crystals on single monolayer WSe2. The colored dashed lines represent the epitaxial orientations aligned with the edges of monolayer WSe2. Scale bar, 50 μm. d Statistical orientation distribution results of epitaxial CsPbI3 on monolayer WSe2.