zemin zheng

The field of two-dimensional (2D) and layered materials continues to excite many researchers around the world who are eager to advance and innovate viable routes for large scale synthesis, doping and integration of monolayers and the development of unique characterization approaches for studying and harnessing exotic properties that will enable novel device applications. There has been a large interest in 2D materials beyond graphene, with particular emphasis on monoelemental materials (phosphorene, silicene, tellurene, etc. ), 2D compounds (MXenes, oxides, nitrides, carbides and chalcogenides), their alloys and layered van der Waals heterostructures. This is not only indicated by the significant increase in the number of peer reviewed publications each year in this area of research, but also by the surging number of conference sessions focusing on 2D materials beyond graphene. This Perspective article highlights some of the recent advances in the field from a diverse inte...

Transition metal dichalcogenides, intercalated with transition metals, are studied for their potential applications as dilute magnetic semiconductors. We investigate the magnetic properties of WSe 2 doped with third-row transition metals (Co, Cr, Fe, Mn, Ti and V). Using density functional theory in combination with Monte Carlo simulations, we obtain an estimate of the Curie or Néel temperature. We find that the magnetic ordering is highly dependent on the dopant type. While Ti and Cr-doped WSe 2 have a ferromagnetic ground state, V, Mn, Fe and Co-doped WSe 2 are antiferromagnetic in their ground state. For Fe doped WSe 2 , we find a high Curie-temperature of 327 K. In the case of V-doped WSe 2 , we find that there are two distinct magnetic phase transitions, originating from a frustrated in-plane antiferromagnetic exchange interaction and a ferromagnetic out-of-plane interaction. We calculate the formation energy and reveal that, ...

Nature Communications, Published online: 10 December 2020; doi:10.1038/s41467-020-20155-7

Hitherto, only circularly polarized antiferromagnetic (AFM) spin-waves (SWs) were expected to convey spin-information. Here, the authors present persistent spin-transport over long distances in the easy-plane AFM phase of hematite, α-Fe2O3, via linearly polarized SW pairs with ultra-low damping.

Molybdenum disulphide (MoS 2 ) and tantalum disulphide (TaS 2 ) are well-known members of the transition metal dichalcogenide (TMD) family. They occur naturally in hexagonal (2H) forms but can also be synthesized in metallic trigonal (1T) phases that are active hydrogen evolution catalysts and exhibit interesting phenomena such as superconductivity and charge density waves. Sparse experimental evidence indicates that 2D crystals of metallic TMDs degrade rapidly in air via an unknown oxidation mechanism. Here we present a computational study on oxidation at the edges and surfaces of 1T-MoS 2 and 1T-TaS 2 monolayers based on density functional theory calculations. Our results suggest that both 1T-MoS 2 and 1T-TaS 2 are very susceptible to oxidation because there are negligible energetic barriers to the dissociation of oxygen molecules at edge sites. However, further oxidation requires the substitution of sulphur atoms by ox...

Single-layer (SL) transition-metal chalcogenides (TMCs) represent an important family of two-dimensional (2D) materials that have attracted intensive research attention recently. It has been established that many TMCs are polymorphic that can exist in different crystal structures and correspondingly exhibit diverse physical properties. Discovery of new structural phases of a crystal is of great scientific and practical importance. In this work, we report a new polymorph of SL-TMC, i.e. SL-Mo 5 Te 8 , attained by molecular-beam epitaxy (MBE). Like the 1 H -MoTe 2 , it possesses the hexagonal symmetry but a much larger unit cell with a basis containing as many as 39 atoms (15 Mo and 24 Te). We call it the variational hexagonal (v1 H ) phase. Coincidently, it may be viewed also as one containing the highest density possible of mirror-twin domain boundaries (MTBs) in an otherwise pristine 1 H -MoTe 2 . Electronically, it is metallic...

Two-dimensional semiconducting transition metal dichalcogenides embedded in optical microcavities in the strong exciton-photon coupling regime may lead to promising applications in spin and valley addressable polaritonic logic gates and circuits. One significant obstacle for their realization is the inherent lack of scalability associated with the mechanical exfoliation commonly used for fabrication of two-dimensional materials and their heterostructures. Chemical vapor deposition offers an alternative scalable fabrication method for both monolayer semiconductors and other two-dimensional materials, such as hexagonal boron nitride. Observation of the strong light-matter coupling in chemical vapor grown transition metal dichalcogenides has been demonstrated so far in a handful of experiments with monolayer molybdenum disulfide and tungsten disulfide. Here we instead demonstrate the strong exciton-photon coupling in microcavities composed of large area transition metal dichalcogen...

We report the successful growth of square-like layered single crystals VOCl with a size of a few millimeters by chemical vapor transport method, and demonstrate that the layered crystals show good air stability and can be easily exfoliated. The atomic-resolution structure of the VOCl single crystals is consistent with the theoretical atomic models and the exfoliated VOCl flakes exhibit a uniform surface potential and a thickness-independent work function in the interval of 4–263 nm. Further magnetic measurements manifest that the VOCl crystal exhibit an N-type ferrimagnetic phase at 150 K and a compensation temperature of ~50 K. These findings not only enrich the magnetic family in layered materials but offer a platform for exploring new physics, and such study of microstructure, air stability, work function and magnetism in layered VOCl should push further the development of functionality tunable microwave devices or spintronics with all-layered materials.

The intrinsic magnetism has long been pursued in two-dimensional (2D) materials down to one-atomic layer thickness. But only very recently, the intrinsic magnetism of monolayer CrI 3 , Fe 3 GeTe 2 , FePS 3 , VSe 2 and bilayer Cr 2 Ge 2 Te 6 are verified in experiment by optical measurement, Raman spectrum and conventional magnetism measurement. Among them, the intralayer exchange interaction of FePS 3 is antiferromagnetic while all the others are ferromagnetic. Most of the ferromagnetic orders in these materials are induce by super exchange interaction. Monolayer Fe 3 GeTe 2 and VSe 2 exhibit metallic character while all the others are semiconductor or insulator. Stable spontaneous magnetization can exist in these monolayer 2D materials because of their strong anisotropy. The anisotropy is mostly from the strong spin–orbit coupling of heavy atoms (CrI 3 , Cr

Two-dimensional (2D) transition metal dichalcogenides (TMDs) offer unique optoelectronic capabilities due to their direct bandgap semiconductor nature in monolayer form. Atomically thin TMDs can be assembled in vertical stacks that are held together by van der Waals forces, enabling interlayer coupling between the layers. This creates new physical properties that depend on the relative orientation (twist angle) between the TMD monolayers. Accurate and fast measurement of the twist angle is therefore of utmost importance for characterizing a 2D TMD heterostructure. Here, we present a nonlinear imaging technique based on second harmonic generation (SHG) microscopy, that enables instantaneous mapping of the twist angle between the two stacked TMD monolayers. By using a polarization beam splitter in the detection path and two detectors measuring two orthogonal SHG polarization components, we acquire with a single-shot measurement the twist angle in a WS 2 /MoS 2 h...

sp 2 -hybridized boron nitride is identified as a strategic material for many purposes related to the integration of graphene and two-dimensional materials in devices and the fabrication of van der Waals heterostructures. Thus, it becomes mandatory to have scalable synthesis and characterization procedures for providing suitable and reliable boron nitride material according to these identified needs. We report here on the growth of sp 2 -hybridized boron nitride film on polycrystalline nickel substrate by chemical vapor deposition with borazine as precursor. We propose a complete study of the influence of the underlying nickel grain orientation on the BN structure layers, in terms of thickness, crystallographic orientation, domain size and stacking. We show the heteroepitaxial growth of continuous, single crystalline hexagonal boron nitride multilayer film on nickel (111)-like grains. We highlight its ABC stacking sequence with AB stacking faults and show how i...

The nano-devices based on atomic layers of nickel dichalcogenides, including NiS 2 , NiSe 2 and NiTe 2 , are rarely studied due to synthetic problems. Recently, ultrathin NiTe 2 nanosheets are reported to be grown on SiO 2 /Si substrate through chemical vapour deposition (CVD). However, the CVD synthesis of other nickel dichalcogenides is still unknown. Here we report the synthesis of NiSe 2 , NiTe 2 and alloy NiSe 2− x Te x (0 < x < 2) nanosheets through a similar CVD method. We found that the growth temperature has great influences on the shape, size and thickness of as-grown nanosheets. When the growth temperature is about 650 °C, the as-grown NiSe 2 and NiTe 2 nanosheets are as thin as 2.7 nm and 3.1 nm, respectively, which is equal to three layers of crystal unit. Combining the transmission electron microscopy and high-angle annular dark fiel...

The number of two-dimensional (2D) materials has grown steadily since the discovery of graphene. Each new 2D material demonstrated unusual physical properties offering a large flexibility in their tailoring for high-tech applications. Here, we report on the formation and characterization of an uncharted 2D material: ‘Cu 2 Te alloy monolayer on Cu(111) surface’. We have successfully grown a 2D binary Te-Cu alloy using a straightforward approach based on chemical deposition method. Low electron energy diffraction (LEED) and scanning tunneling microscopy (STM) results reveal the existence of a well-ordered alloy monolayer characterized by (√3 × √3)R30° superstructure, while the x-ray photoemission spectroscopy (XPS) measurements indicate the presence of single chemical environment of the Te atoms associated with the Te-Cu bonding. Analysis of the valence band properties by angle resolved photoemission spectroscopy (ARPES); in particular the electronic states close to the F...