We
demonstrate a general protocol that uses a metastable phase
as a template, followed by chalcogen substitution and phase transformation
to obtain superlattices, or single crystals, of layered transition
metal dichalcogenides (TMDs). In particular, the single-crystalline
2H-MoTe2 thin film, with the available wafer-scale synthesis,
is selected as the template to study the chalcogen substitution mechanism.
Analogous to the initiation polymerization process, a Te vacancy-initiated
and S diffusion-mediated mechanism is proposed to describe the sequential
substitution: the complete sulfurization of the top and bottom MoTe2 layers at the first stage, followed by the alloying process
in the middle layers and finally the full conversion of the flake
into MoS2. The substitution in each layer starts from the
vacancy and expands to the nearby region catalyzed by the strain field,
whereas the sulfurization sequence in the multilayer system is mediated
by the cross-layer S diffusion process. This is confirmed by the cross-sectional
observation of the intermediate state by scanning transmission electron
microscopy and density functional theory studies. This unique mechanism
enables us to fabricate the sub-centimeter scale, composition-tunable,
and symmetric MoS2/MoTe2(1–x)S2x
/MoS2 superlattices.
Our work presents a new tool for the large-scale synthesis of TMD-based
heterostructures toward industrial applications.
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