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

Abstract

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 with freestanding few-layer TMPTs, with the aim of tailoring their properties. The irradiation-induced structure modifications were systematically investigated by various transmission electron microscopy methods on FePS 3 , MnPS 3 , and NiPS 3 , 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, predominant removal of sulfur by the impinging electrons, thus showing the possibility of tuning 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 ultra-thin freestanding TMPTs by controlling their stoichiometry.

Electron-Beam- and Thermal-Annealing-Induced Structural Transformations in Few-Layer MnPS3

“…As shown in our previous study, a primary removal of sulfur (S) and phosphorus (P) atoms by 80 keV electrons is favored via direct electron−nucleus collision. 61 This leads to an S deficiency in electron beam exposed regions of few-layer MnPS 3 (see Figure S3) and, therefore, can lead to the growth of new structures.…”

“…The white line ratio 71 of L 3 to L 2 gives a value of 4.50, which suggests that the structure mainly contains Mn(2+). 61,71 Selected area electron diffraction experiments were performed on the annealed sample as well (see Figure S10a), and an azimuthally integrated (elliptical distortion corrected) pattern is shown in Figure 4d. A simulated powder diffraction pattern of alabandite�face-centered-cubic Mn 2+ S 2− �is shown in red.…”

“…To determine the valence, core-loss EELS of the Mn-L 2,3 edge is performed and presented in Figure c. The white line ratio of L 3 to L 2 gives a value of 4.50, which suggests that the structure mainly contains Mn­(2+). , …”

“…60 Our recent TEM study already showed that few-layer TMPTs predominantly lose sulfur as a result of their interaction with the impinging electrons, which in turn leads to strong modifications of the pristine material. 61 However, the change in properties of freestanding few-layer MnPS 3 /MnS systems due to electron-beam-induced phase transformations and due to annealing has not been investigated so far in detail.…”

“…For instance, α-MnS was proposed as an anode material for postlithium batteries − and an interesting candidate for future electronic devices: e.g., in field-effect transistors . Our recent TEM study already showed that few-layer TMPTs predominantly lose sulfur as a result of their interaction with the impinging electrons, which in turn leads to strong modifications of the pristine material …”