High-Energy Electron Beam Irradiation as a Tool for Tailoring the Properties of CVD-Grown ReS ₂ Films

Particle irradiation, particularly high-energy electron beams (e-beams), serves as an effective tool for engineering the physical and chemical properties of two-dimensional transition metal dichalcogenides (2D TMDs). In this study, chemical vapor deposition (CVD)-grown rhenium disulfide (ReS2) films were subjected to electron beam irradiation at varying fluences to investigate the resulting modifications in the material characteristics. Through X-ray diffraction (XRD) and detailed X-ray photoelectron spectroscopy (XPS), we have deduced that incident e-beams can break the Re–S bond that results in reducing crystallinity as well as a change in stoichiometry of the film. The XPS analysis also shows that the elemental sulfur, released from the breaking of the Re–S bonds, gets accumulated near the surface, and its concentration increases with the exposure dose. The accumulation of sulfur on the surface is further verified using depth-profile XPS and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The experimental results were further corroborated by density functional theory (DFT) calculations. Our study points out that the release of sulfur from lattice positions and accumulation near the surface have two important effects on the material characteristics. (i) The exposure to high-energy electron beams leads to the creation of sulfur vacancies whose concentration increases with the exposure dose. Sulfur vacancies introduce n-type doping, resulting in higher current in the I–V measurements, and (ii) the accumulated elemental sulfur near the surface is accountable for the change in refractive index of the films measured by the ellipsometry technique. The elemental sulfur results in reduced absorption and enhanced reflection in the exposed films as compared to the unexposed ReS2 films, causing an increase in the refractive index. These results demonstrate that e-beam irradiation serves as a tool for tuning the optical and electrical properties of ReS2 films, paving the way for their integration into advanced optoelectronic applications.