Band alignment estimation of MoS2/g-C3N4 thin-film S-scheme heterojunction based on surface potential measurements

Abstract

Energy band alignment of thin-film heterojunction of molybdenum disulfide (MoS₂) and polymeric carbon nitride (g-C₃N₄)has been investigated, which can be regarded as a model system of heterojunction photocatalysts. A bilayer of MoS₂ and g-C₃N₄ (MoS₂/g-C₃N₄) with an exposed platinum (Pt) bottom electrode was fabricated by thermal chemical vapor deposition and sulfur hexafluoride-based dry etching, followed by deposition of MoS₂ nanosheets on top of that via tape exfoliation and elastomer-assisted transfer techniques. Simultaneous imaging of topography and surface potential over MoS₂/g-C₃N₄ on Pt was performed by using Kelvin probe force microscopy (KPFM) in dark. The energy band alignment of MoS₂/g-C₃N₄ on Pt was estimated based on the KPFM imaging results and other physical properties of individual MoS₂ and g-C₃N₄ samples examined with ultraviolet photoelectron spectroscopy and ultraviolet-visible absorption spectroscopy. In addition, photo-induced change in the surface potential over MoS₂/g-C₃N₄ on Pt was measured to consider the behavior of photo-induced carriers therein.The depicted energy band alignment having band bending in MoS₂ layer suggests the possibility of S-scheme heterojunction formation at MoS₂/g-C₃N₄ interface.