Direct Growth of Monolayer WS2 on Rutile TiO2 for Enhanced Valley Coherence

Monolayer transition-metal dichalcogenides (TMDs) have registered attractive potential applications in optoelectronics, spintronics, and valleytronics. Here, we develop a simple chemical vapor deposition method to directly grow large-size monolayer WS2 on an atomically flat rutile TiO2(110) substrate. The variety of microscopic and spectroscopic characterizations reveals the highly single crystallinity of the as-grown WS2 and the atomically clean WS2/TiO2 interface. Such structural perfection renders a neutral excitonic photoluminescence of WS2 with extremely small spectral broadening of around 20 meV at cryogenic temperature. Moreover, the low concentration of defect leads to the suppressed intervalley scattering, while the efficient interfacial electron transfer reduces the Coulomb interaction between the valleys of the WS2, which thus enhance the valley polarization and coherence significantly so that it can reserve up to room temperature under ambient conditions. These results demonstrate that the substrate tuning corroborated by interface control can be a promising strategy to utilize the TMDs in practical valleytronics.