Property Changes Induced by Proton Irradiation of Graphene/WS₂ van der Waals Heterostructure

Van der Waals (vdW) heterostructures have attracted significant attention due to their ability to tune the physical and chemical properties of two-dimensional (2D) materials. Monolayer (ML) graphene and 2D transition metal dichalcogenide (TMD) heterostructures have been extensively studied. Depending on Fermi level alignment, electron transfer occurs from TMD to graphene or vice versa. In such heterostructures, ML graphene serves as a fast channel for excited carriers, enhancing the separation of electron-hole pairs. This leads to tunable electrical and optical properties—such as electron-hole recombination rates and optical absorption—not achievable by either material alone Additionally, defect engineering offers further control over the properties of 2D materials. Generating defects such as dislocations, nanopores and vacancies, it is able to control electronic, optical and magnetic properties by tuning excitonic states and band structure. Proton irradiation is one method used for defect engineering, capable of inducing changes in defect geometry, phase transformation, and crystallinity. nanopores generated by proton irradiation in exfoliated ML WS₂ have been shown to enhance exciton-to-trion conversion without affecting material homogeneity or crystallinity, by creating in-gap states favorable for trion formation. Building on these methods, we demonstrate property changes in proton-irradiated ML graphene and monolayer TMD heterostructures. The ML materials are prepared by mechanical exfoliation, and transferred onto a SiO₂ substrate to form a heterostructure by staking ML WS₂ on ML graphene. Atomic force microscopy is used to confirm the staked bilayer structure through topographical images. Raman spectroscopy and photoluminescence measurements are performed to investigate property changes and carrier transfer of ML graphene and ML WS₂ before and after heterostructuring and proton irradiation. Transmission electronic microscopy is also employed to analyze the defect structures generated by proton irradiation. Our results show that the properties of semiconductors can be controlled through heterostructuring with graphene, and defect introduction via proton irradiation. This presents a promising route to achieving desirable properties for applications such as advanced optoelectronic and spintronic devices, which are unattainable with separate graphene or 2D TMDs.