Unconventional Enhancement of Photoluminescence in Multilayer MoS2 within MoS2/MoO2 Heterostructures: Implication for Optoelectronic Devices

Monolayer two-dimensional (2D) transition-metal chalcogenides (TMDs) with a direct bandgap are promising in future optoelectronics due to the strong light-matter interaction. Comparatively speaking, their multilayer counterparts show a higher carrier mobility and current capacity over the monolayer. However, multilayer TMDs with an indirect bandgap exhibit weak photoluminescence (PL) emission, hindering their practical applications. In this work, we discovered an unconventional PL enhancement of multilayer MoS2 in chemical vapor-deposited MoS2/MoO2 heterostructures, whose intensity is an order of magnitude higher than that observed in multilayer MoS2 on SiO2/Si. The PL enhancement is mainly attributed to the surface plasmon resonance of MoO2, as evidenced by UV-vis absorption spectroscopy of the MoS2/MoO2 heterostructures and the laser wavelength selectivity of the PL enhancement. Meanwhile, a nanogap was observed at the interface of MoS2 and MoO2 by using high-resolution scanning transmission electron microscopy, which impedes the PL quenching induced by the charge transfer between multilayer MoS2 and metallic MoO2. To confirm the mechanism, MoS2/BN/MoO2 heterostructures were assembled by using insulating monolayer boron nitride (BN) to simulate the nanogap, and similar PL enhancement of multilayer MoS2 was observed. To the best of our knowledge, surface plasmon resonance-enhanced PL emission by a metal oxide substrate has been rarely reported until now. This work provides a platform for regulating the light-matter interaction of 2D materials, which will benefit their applications in optoelectronic devices.