Phase transformations in single-layer MoTe2stimulated by electron irradiation and annealing.

Among two-dimensional (2D) transition metal dichalcogenides (TMDs), MoTe2is predestined for phase-engineering applications due to the small difference in free energy between the semiconducting H-phase and metallic 1T'-phase. At the same time, the complete picture of the phase evolution originating from point defects in single-layer of semiconducting H-MoTe2via Mo6Te6nanowires to cubic molybdenum has not yet been reported so far, and it is the topic of the present study. The occurring phase transformations in single-layer H-MoTe2were initiated by 40-80 kV electrons in the spherical and chromatic aberration-corrected high-resolution transmission electron microscope and/or when subjected to high temperatures. We analyse the damage cross-section at voltages between 40 kV and 80 kV and relate the results to previously published values for other TMDs. Then we demonstrate that electron beam irradiation offers a route to locally transform freestanding single-layer H-MoTe2into one-dimensional (1D) Mo6Te6nanowires. Combining the experimental data with the results of first-principles calculations, we explain the transformations in MoTe2single-layers and Mo6Te6nanowires by an interplay of electron-beam-induced energy transfer, atom ejection, and oxygen absorption. Further, the effects emerging from electron irradiation are compared with those produced byin situannealing in a vacuum until pure molybdenum crystals are obtained at temperatures of about 1000 °C. A detailed understanding of high-temperature solid-to-solid phase transformation in the 2D limit can provide insights into the applicability of this material for future device fabrication.

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

Quasi-two-dimensional (2D) manganese phosphorus trisulfide, MnPS3, 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 MnPS3 by local structural transformations via electron irradiation in a transmission electron microscope and by thermal annealing under vacuum. In both cases we find that MnS1-xPx phases (0 ≤ x < 1) form in a crystal structure different from that of the host material, namely that of the α- or 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 MnPS3.

In Situ Crystallization of the Insoluble Anhydrite AII Phase in Graphene Pockets.

Single-distilled water encapsulated in graphene pockets has been studied by aberration-corrected high-resolution transmission electron microscopy and electron energy loss spectroscopy at an acceleration voltage of 80 kV. Inside the graphene pockets, crystallization and in situ crystal growth are reported and identified as the insoluble AII phase of CaSO4 (anhydrite) in a quasi-two-dimensional system. Its formation condition is discussed with respect to the possible temperature and van der Waals pressure between the graphene sheets.

A High-Voltage and High-Capacity Li1+x Ni0.5 Mn1.5 O4 Cathode Material: From Synthesis to Full Lithium-Ion Cells.

We report Co-free, Li-rich Li1+x Ni0.5 Mn1.5 O4 (0