Structural and Chemical Modifications of Few-layer Transition Metal Phosphorous Trisulfides by Electron Irradiation

Transition metal phosphorous trisulfides (TMPTs) are inorganic materials with inherent magnetic properties. Due to their layered structure, they can be exfoliated into ultra-thin sheets, which show properties different from their bulk counterparts. Herein, we present a detailed analysis of the interaction of the electron beam (30 – 80 kV) in a transmission electron microscope (TEM) with freestanding few-layer TMPTs, with the aim to tailor their properties. The irradiation-induced structure modifications were systematically investigated by various TEM methods on FePS3, MnPS3, and NiPS3, and the results are rationalized with the help of ab-initio calculations, which predict that the knock-on threshold for removing sulfur is significantly lower than that for phosphorus. Therefore, a targeted removal of sulfur is feasible. Eventually, our experiments confirm the dose-dependent, predominantly removal of sulfur by the impinging electrons, thus showing the possibility to tune the sulfur concentration. Using ab-initio calculations, we analyze the electronic structure of the TMPTs with single vacancies and oxygen impurities, and predict distinct electronic properties depending on the type of defect. Therefore, our study shows the possibility of tuning the properties of ultrathin freestanding TMPTs by controlling their stoichiometry.