Mo Doping Assisting the CVD Synthesis of Size-Controlled, Uniformly Distributed Single-Layer MoS 2 on Rutile TiO 2 (110).

Molybdenum disulfide (MoS ₂ ) 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 MoS ₂ on various substrates. However, it remains a great challenge to fabricate high-quality MoS ₂ 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 MoO ₃ first followed by subsequent vulcanization, to grow single-layer MoS ₂ on an atomically flat rutile TiO ₂ (110) (r-TiO ₂ (110)) substrate. This method not only very well controls the size as well as the spatial distribution of MoS ₂ nanosheets over the TiO ₂ 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 MoS ₂ derives from the sulfurization of the singly dispersed Mo ⁶⁺ and Mo ⁵⁺ species in the surface/subsurface region instead of the aggregated MoO ₃ patches on top of the TiO ₂ surface. Such a mechanism may dictate a general way for synthesizing high-quality transition-metal dichalcogenides (TMDs) over a variety of functional substrates.