Influence of van der Waals epitaxy on phase transformation behaviors in 2D heterostructure

Despite exhibiting their attractive properties and performances, the interlayer interaction in two-dimensional van der Waals epitaxy heterostructures is not well understood. Here, we demonstrate the growth of two dimensional vertically stacked multilayer β-In₂Se₃/monolayer WS₂ heterostructures via the chemical vapor deposition method. Despite a large lattice misfit (29.9%), the vertically stacked β-In₂Se₃/WS₂ heterostructures exhibit van der Waals epitaxy with well-aligned lattice orientation of WS₂(100)[001]//In₂Se₃(100)[001], forming a periodic superlattice. Interestingly, a reversible phase transformation of epitaxial β-In₂Se₃ has been observed by temperature-dependent Raman spectroscopy and electron diffraction conducted from liquid N₂ to room temperature. Notably, the phase transformation of epitaxial β-In₂Se₃ can only be observed when its layer number is larger than 4 and the transformation temperature increases with the increase in the layer number, indicating a layer number dependent phase transformation of epitaxial β-In₂Se₃. These results indicate that the confinement effect exists between monolayer WS₂ and epitaxial β-In₂Se₃, strongly constraining the lattice change of adjacent few layers of β-In₂Se₃.