Phase controllable synthesis of 2D materials is of significance for tuning related electrical, optical, and magnetic properties. Herein, the phase‐controllable synthesis of tetragonal and hexagonal FeTe nanoplates has been realized by a rational control of the Fe/Te ratio in a chemical vapor deposition system. Using density functional theory calculations, it has been revealed that with the change of the Fe/Te ratio, the formation energy of active clusters changes, causing the phase‐controllable synthesis of FeTe nanoplates. The thickness of the obtained FeTe nanoplates can be tuned down to the 2D limit (2.8 nm for tetragonal and 1.4 nm for hexagonal FeTe). X‐ray diffraction pattern, transmission electron microscopy, and high resolution scanning transmission electron microscope analyses exhibit the high crystallinity of the as‐grown FeTe nanoplates. The two kinds of FeTe nanoflakes show metallic behavior and good electrical conductivity, featuring 8.44 × 104 S m−1 for 9.8 nm‐thick tetragonal FeTe and 5.45 × 104 S m−1 for 7.6 nm‐thick hexagonal FeTe. The study provides an efficient and convenient route for tailoring the phases of FeTe nanoplates, which benefits to study phase‐sensitive properties, and may pave the way for the synthesis of other multiphase 2D nanosheets with controllable phases.
Doping can change the intrinsic properties of 2D materials by tuning their electronic structure. In this work, high‐quality 2D In‐doped SnS2 (In‐SnS2) monolayer is reported through chemical vapor transport method and following mechanical cleavage process. The In content of In‐SnS2 is ≈0.9%, and doping results in the downward shift of the Fermi level compared with the undoped one. Transmission electron microscopy images show that doping is uniform in the In‐SnS2 nanosheets with high quality. The In‐SnS2 monolayer field effect transistors (FETs) show p‐type feature which is different from the n‐type feature of undoped SnS2. The average hole produced by one In atom is estimated as 0.37 from FETs measurement. Density functional theory calculations show that the decreasing of hole concentration results from the hole killing mechanism induced by S vacancy. The results suggest that changing the polarity of 2D semiconductor by doping is successful, and In‐SnS2 monolayer has great potential in the applications of electronics and optoelectronics.
Two-dimensional (2D) magnetic materials have aroused tremendous interest due to the 2D confinement of magnetism and potential applications in spintronic and valleytronic devices. However, most of the currently 2D magnetic materials are achieved by the exfoliation from their bulks, of which the thickness and domain size are difficult to control, limiting the practical device applications. Here, we demonstrate the realization of thickness-tunable rhombohedral Cr2Se3 nanosheets on different substrates via the chemical vapor deposition route. The magnetic transition temperature at about 75 K is observed. Furthermore, van der Waals heterostructures consisting of Cr2Se3 nanosheets and monolayer WS2 are constructed. We observe the magnetic proximity effect in the heterostructures, which manifests the manipulation of the valley polarization in monolayer WS2. Our work contributes to the vapor growth and applications of 2D magnetic materials.
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