Fig. 1: Epitaxial growth of wafer-scale NbS2 films via metal-organic chemical vapor deposition (MOCVD).
a Schematic illustration of the four-stage epitaxial growth process of NbS2 on a 2-inch c-plane sapphire wafer: (i) preferential crystallization at terrace step edges; (ii) self-templated epitaxial multilayer growth; (iii) domain merging and grain stitching; and (iv) formation of a continuous epitaxial film. b–e Atomic force microscopy (AFM) and optical images corresponding to the sequential growth stages illustrated in (a). The white dashed lines in (b)&(c) represent terrace steps on sapphire substrates. Scale bars of (c–e): 30 μm. f Schematic of self-templated concurrent epitaxial growth of NbS2. Adatoms incorporate both along the basal-plane edges (horizontal arrows) and onto existing terraces (vertical arrows), enabling simultaneous lateral expansion and vertical stacking. g High-resolution AFM image showing a single-crystalline NbS2 domain confined by atomic terrace steps on the sapphire substrate. The white dashed lines represent terrace steps on sapphire substrates, and the height profile of as-grown NbS2 domain is 3 nm. h Calculated phase diagram showing the growth regimes as a function of the precursor flux ratio Γ = Fseed/(Fgas+Fseed) and the normalized surface diffusion length Λ = ℓ/L0. Fseed represents the initial Nb flux released from the spin-coated NbCl5 layer, Fgas is the continuous gaseous precursor supply during MOCVD, ℓ denotes the adatom diffusion length, and L0 corresponds to the initial nucleus size.
