Mo Doping Assisting the CVD Synthesis of Size-Controlled, Uniformly Distributed Single-Layer MoS₂ on Rutile TiO₂(110)

Molybdenum disulfide (MoS₂) has attracted considerable interest due to its superior electronic and optical properties, which have seen promising applications in optoelectronics and catalysis. Chemical vapor deposition (CVD) has been successfully applied in synthesizing MoS₂ on various substrates. However, it remains a great challenge to fabricate high-quality MoS₂ sheets with well-controlled micro/nano size and homogeneous distribution over the functional substrates such as active metal oxides. Herein, we have developed a two-step synthetic strategy via depositing MoO₃ first followed by subsequent vulcanization, to grow single-layer MoS₂ on an atomically flat rutile TiO₂(110) (r-TiO₂(110)) substrate. This method not only very well controls the size as well as the spatial distribution of MoS₂ nanosheets over the TiO₂ surface but also averts the formation of contaminative species at the heterojunction while maintaining the atomic structure of the substrate surface. The extensive characterizations reveal that the formation of MoS₂ derives from the sulfurization of the singly dispersed Mo⁶⁺ and Mo⁵⁺ species in the surface/subsurface region instead of the aggregated MoO₃ patches on top of the TiO₂ surface. Such a mechanism may dictate a general way for synthesizing high-quality transition-metal dichalcogenides (TMDs) over a variety of functional substrates.