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.