Programmable Interfacial Band Configuration in WS2/Bi2O2Se Heterojunctions

Abstract

van der Waals heterojunctions based on transition-metal dichalcogenides (TMDs) offer advanced strategies for manipulating light-emitting and light-harvesting behaviors. A crucial factor determining the light-material interaction is in the band alignment at the heterojunction interface, particularly the distinctions between type-I and type-II alignments. However, altering the band alignment from one type to another without changing the constituent materials is exceptionally difficult. Here, utilizing Bi₂O₂Se with a thickness-dependent band gap as a bottom layer, we present an innovative strategy for engineering interfacial band configurations in WS₂/Bi₂O₂Se heterojunctions. In particular, we achieve tuning of the band alignment from type-I (Bi₂O₂Se straddling WS₂) to type-II and finally to type-I (WS₂ straddling Bi₂O₂Se) by increasing the thickness of the Bi₂O₂Se bottom layer from monolayer to multilayer. We verified this band architecture conversion using steady-state and transient spectroscopy as well as density functional theory calculations. Using this material combination, we further design a sophisticated band architecture incorporating both type-I (WS₂ straddles Bi₂O₂Se, fluorescence-quenched) and type-I (Bi₂SeO₅ straddles WS₂, fluorescence-recovered) alignments in one sample through focused laser beam (FLB). By programming the FLB trajectory, we achieve a predesigned localized fluorescence micropattern on WS₂ without changing its intrinsic atomic structure. This effective band architecture design strategy represents a significant leap forward in harnessing the potential of TMD heterojunctions for multifunctional photonic applications.

Keywords: 2D materials; band alignment; fluorescence design; heterojunctions; laser modification.