Programmable Interfacial Band Configuration in WS/BiOSe Heterojunctions.

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 BiOSe with a thickness-dependent band gap as a bottom layer, we present an innovative strategy for engineering interfacial band configurations in WS/BiOSe heterojunctions. In particular, we achieve tuning of the band alignment from type-I (BiOSe straddling WS) to type-II and finally to type-I (WS straddling BiOSe) by increasing the thickness of the BiOSe 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 (WS straddles BiOSe, fluorescence-quenched) and type-I (BiSeO straddles WS, fluorescence-recovered) alignments in one sample through focused laser beam (FLB). By programming the FLB trajectory, we achieve a predesigned localized fluorescence micropattern on WS 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.