Reactively liquid eutectic salts intermediated CVD growth and photoelectric properties of MoSe2/Graphene heterojunction

Abstract

Transition metal chalcogenides (TMDs)/graphene heterojunctions are considered as potential materials of high-performance photodetectors in a prerequisite of controllable preparation. Here, we propose a salt-assisted chemical vapor deposition with pre-spin-coating precursors to advance the fabrication of MoSe₂/graphene heterojunctions, in which Se vapor and H₂ gas are transported to react with the molten Na₂MoO₄ and NH₄Cl salts atop the graphene layer for the MoSe₂ growth. The effects of H₂ flowrate, temperature and time of reaction, composition and ratio of elements in the salt precursors, as well as the layer number of graphene film, are investigated. The results demonstrate that a liquid eutectic salt complex, consisting of sodium-molybdenum-oxyhalide, is an essential transient intermediate, and the growth follows a novel vapor–liquid/vapor–solid (V–L/V–S) mechanism. By optimizing the growth parameters, MoSe₂/graphene heterojunctions with the monolayer up to 80 % of MoSe₂ are synthesized with the lattice alignment of graphene (100) to MoSe₂ (100). The interaction between graphene and MoSe₂ is monitored by the Raman, UV–Vis and PL spectra. Additionally, carrier inversion phenomenon in MoSe₂/graphene heterojunction is found relying on the light illumination intensity. These results contribute new insights into the controllable synthesis and fascinating properties of graphene-based TMDs heterojunctions.