Constructed WS2-TiO2 model for robust interfacial charge transfer modulation via facet-dependent strategy

Abstract

Regulating interfacial charge transfer is vital for the optoelectronic and photocatalytic applications of semiconductive heterostructures consisting of transition metal dichalcogenides (TMDCs) and transitional metal oxides (TMOs). This process typically relies on external field modulation and materials design. However, limited synthetic approaches and microscopic investigations have hindered the fundamental understanding of facet-dependent effects in TMDCs/TMO. In this study, we have fabricated the high-quality WS₂/TiO₂ model system, combining monolayer WS₂ nanosheets on atomically flat rutile TiO₂ single-crystal substrates with distinct facets through a chemical vapor deposition (CVD) method. Photoluminescence (PL) spectroscopy shows that the excitonic response of WS₂ is facet-dependent, with A⁰/A⁻ exciton ratio decreasing in the order (1 0 0) > (1 1 0) > (1 1 1) > (0 0 1), indicating that charge transfer follows the evolution of crystallographic orientation. Kelvin probe force microscopy (KPFM) reveals the same sequence in interfacial electric fields, reflecting facet-dependent charge-transfer efficiency. Under ultraviolet illumination, the surface-potential dynamics further demonstrate enhanced interfacial charge transfer. A similar interfacial charge transfer regulation process has been further extended to the MoS₂/TiO₂ system. These findings underline the oxide facet engineering as a potential strategy for optimizing the interfacial effect in TMDCs/TMO heterostructures, which also paves the way for their applications in energy conversion and catalysis.