Growth-Pathway-Controlled van der Waals Epitaxy of Phase-Selective Tin Sulfides.

Controlling crystalline phase and interfacial strain remains a central challenge in van der Waals (vdW) epitaxy for polymorphic two-dimensional (2D) materials. Tin sulfides represent an ideal platform, yet deterministic phase control and growth-pathway effects on phase stability and strain accommodation remain unexplored. Here, we demonstrate growth-pathway-controlled vdW epitaxy of phase-selective tin sulfides on WSe2 using a two-zone chemical vapor deposition (CVD) system. Under sulfur-rich conditions, tin sulfide adopts a hexagonal SnS2 structure that shares the trigonal symmetry of WSe2, enabling a unique in-plane epitaxial alignment despite a large lattice mismatch. Under sulfur-deficient conditions, tin sulfide stabilizes in orthorhombic SnS, whose symmetry is incompatible with WSe2. As a result, SnS nucleates with multiple energetically comparable epitaxial registries. Direct growth of SnS on WSe2 generates substrate-mediated strain, leading to local lattice distortion and phase evolution from α- to β'-SnS. Through sequential control of the precursor temperature, SnS is grown on a pre-formed SnS2 rather than directly on WSe2. This sequential growth suppresses substrate-induced strain and yields deformation-free α-SnS via a SnS2 vdW buffer layer. These findings establish growth-pathway-controlled vdW epitaxy as a strategy for decoupling epitaxial alignment from strain accommodation, enabling deterministic phase control and structural integrity in lattice-mismatched vdW heterostructures.