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

Abstract

Quasi-two-dimensional (2D) manganese phosphorus trisulfide, MnPS 3 , which exhibits antiferromagnetic ordering, is a particularly interesting material in the context of magnetism in a system with reduced dimensionality and its potential technological applications. Here, we present an experimental and theoretical study on modifying the properties of freestanding MnPS 3 by local structural transformations via electron irradiation in a transmission electron microscope and by thermal annealing under vacuum. In both cases we find that MnS 1−x P x phases (0 ≤ x < 1) form in a crystal structure different from that of the host material, namely that of the αor γ-MnS type. These phase transformations can both be locally controlled by the size of the electron beam as well as by the total applied electron dose and simultaneously imaged at the atomic scale. For the MnS structures generated in this process, our ab initio calculations indicate that their electronic and magnetic properties strongly depend on both in-plane crystallite orientation and thickness. Moreover, the electronic properties of the MnS phases can be further tuned by alloying with phosphorus. Therefore, our results show that electron beam irradiation and thermal annealing can be utilized to grow phases with distinct properties starting from freestanding quasi-2D MnPS 3 .

Structural Transformations in Few-Layer MnPSe3 Stimulated by Thermal Annealing and Electron Irradiation

“…In addition, an isolated hexagonal γ-MnSe crystal viewed along the [0001] direction is depicted in Figure e, and more examples of MnSe crystals are given in Figure S7. One additional observation is that the emerging freestanding nanocrystals have a much smaller lateral extent and are less frequent than those found in MnPS 3 . Further, these nanocrystals are surrounded by large amorphous areas, which can be inferred from the presented EDX results (cf.…”

“…This type of damage process at 80 kV in MnPSe 3 is different from that in few-layer MnPS 3 , where mainly elastic damage and subsequent sputtering were reported as a significant damage mechanism . The difference in electron-specimen interaction can partially explain why no direct emergence of new phases was observed, as in the case of MnPS 3 . , It has to be noted that in the work of Roccapriore et al, it is stated that no direct emergence of new phases in MnPSe 3 due to electron irradiation was observed. Yet, they mentioned that they could identify Se defects in HAADF-STEM images, which were acquired at 60 kV.…”

“…Electron beam-induced damage in the TEM can alter the atomic structure of 2D materials, and thus, exposure to the beam can significantly influence the material properties. − At the same time, when the damage process can be controlled, , TEM can be utilized as a tool to tailor the structure on the atomic scale . In particular, TEM was utilized in several studies to produce single ,,, as well as extended defects. − In some cases, even complete phase transformations stimulated by electron irradiation were reported, − which can significantly affect the properties of the investigated material. ,, Moreover, additional pathways such as in situ TEM can be followed to study modifications of other stimuli on the atomic scale in TEM in real time. − Therefore, TEM is a paramount tool in investigating structural transformations in 2D materials by different stimuli. , …”

“…Furthermore, strong modifications of the structure and properties of few-layer transition metal phosphorus trisulfides caused by electron irradiation were reported. ,, A predominant removal of sulfur in few-layer TMPTs by electron irradiation in the low-voltage regime (i.e., 30–80 kV) in TEM was observed. ,, Calculations revealed that the elastic knock-on displacement threshold of S is significantly lower compared to, for instance, MoS 2 or MoSe 2 . , Thus, elastic damage plays a significant role in investigating transition metal phosphorus trisulfides in TEM above 50 kV. , Further, inelastic damage channels cause the primary removal of S in TMPTs as well below the knock on threshold . In particular, it was shown that intriguing phase transformations in few-layer MnPS 3 can be stimulated by electron irradiation , as well as annealing in vacuum . At the same time, beam damage mechanisms in the few-layer regime have been less studied in MnPSe 3 compared to MnPS 3 .…”

Machine-learning-accelerated screening of single metal atoms anchored on MnPS3 monolayers as promising bifunctional oxygen electrocatalysts

“…To thus address these questions, it is critical to properly evaluate the feasibility of the anchoring of SACs on MPS 3 and reveal the detailed mechanism of SACs on ORR/ OER. Compared with other MPS 3 materials, the experimental synthesis technology of the MnPS 3 monolayer is the most mature; 46,47 thus, we chose MnPS 3 as a representative of MPS 3 for supporting SACs.…”