Tuning photoluminescence behaviors in strained monolayer belt-like MoS2 crystals confined on TiO2(001) surface

We report on a monolayer (ML) MoS₂ belt-like single crystal directly fabricated on the Rutile-TiO₂(001) surface via chemical vapor deposition (CVD). We find that the photoluminescence (PL) behaviors in the ML MoS₂ single crystal strongly depend on their shapes and the interface of MoS₂/TiO₂. Compared with the as-grown triangular ML MoS₂, the PL peak position is in a blue shift and the PL intensity is increased for the as-grown ML MoS₂ belt. Moreover, the PL peak position is in the blue shift by about 38 meV and the intensity is enhanced by nearly 15 times for the as-grown ML MoS₂ belt crystal on TiO₂ than those samples transferred onto SiO₂/Si substrate. This special PL behavior can be attributed to the in-plane compressive strain that is introduced during the CVD growth of ML MoS₂ belts confined by the substrate. The energy band of the strained ML MoS₂ belt is changed with an up-shift in the conduction band minimum (VBM) and a down-shift in the valence band maximum (CBM), and the band gap is thus enlarged. This results in the energy band structural realignment in the interface of MoS₂/TiO₂, thereby weakening the charge transferring from the TiO₂ substrate to MoS₂ and suppressing the concentration of charged excitons to finally enhance the PL intensity of the ML MoS₂ belt. The substrate-confined ML MoS₂ belts provide a new route for tailoring light-matter interactions to upgrade their weak quantum yields and low light absorption, which can be utilized in optoelectronic and nanophotonic devices.