Jiuxiang Dai

Metallic/semimetallic transition metal dichalcogenides (m-TMDs) have grabbed widespread attention in recent years due to their exotic physical properties and potential applications in various fields. The state-of-the-art progress in m-TMDs is reviewed, including electronic and crystal structures, synthetic methods, physical properties, and practical applications. Moreover, views on development, challenges, and future prospects of m-TMDs are put forward.

Abstract

2D materials and the associated heterostructures define an ideal material platform for investigating physical and chemical properties, and exhibiting new functional applications in (opto)electronic devices, electrocatalysis, and energy storage. 2D transition metal dichalcogenides (2D TMDs), as a member of the 2D materials family including 2D semiconducting TMDs (s-TMDs) and 2D metallic/semimetallic TMDs (m-TMDs) have attracted considerable attention in the scientific community. Over the past decade, the 2D s-TMDs have been extensively researched and reviewed elsewhere. Because of their distinctive physical properties including intrinsic magnetism, charge-density-wave order and superconductivity, and potential applications, such as high-performance electronic devices, catalysis, and as metal electrode contacts, 2D m-TMDs have grabbed widespread attention in recent years. However, reviews demonstrating the m-TMDs systematically and comprehensively have been rarely reported. Here, the recent advances in 2D m-TMDs in the aspects of their unique structures, synthetic approaches, distinctive physical properties, and functional applications are highlighted. Finally, the current challenges and perspectives are discussed.

A patterning method for van der Waals materials is introduced to pattern the materials via highly intensive light at multiple scales, high throughput, and high resolution. The method has scalability in types of materials and substrates and does not result in accompanying polymeric residues on the surface of the patterned materials unlike conventional photolithography. Simulations confirm that the intensive light allows high resolution patterning.

Abstract

Advanced patterning techniques are essential to pursue applications of 2D van der Waals (vdW) materials in electrical and optical devices. Here, the direct optical lithography (DOL) of vdW materials by single-pulse irradiation of high-power light through a photomask is reported. The DOL exhibits large-scale patterning with a sub-micrometer resolution and clean surface, which can be applied to various combinations of vdW materials and substrates. In addition, the thermal profile during DOL is investigated using the finite element method, and the ideal conditions of DOL according to the materials and substrates are determined.

The recent progress of MXenes synthesis strategies, including etching, intercalation, and delamination, is summarized. The large-scale preparation methods for MXenes and their derivates, such as flexible membranes and fibers, are discussed. Moreover, the understanding of the oxidation stability of MXenes and stable storage strategies are also addressed.

Abstract

2D transition metal carbides, nitrides, and carbonitrides, also known as MXenes, are versatile materials due to their adjustable structure and rich surface chemistry. The physical and chemical diversity has recognized MXenes as a potential 2D material with a wide spectrum of application domains. Since the discovery of MXenes in 2011, a wide variety of synthetic routes has been proposed with advancement toward large-scale preparing methods for MXene nanosheets and derivative products. Herein, the critical synthesis aspects and the operating conditions that influence the physical and chemical characteristics of MXenes are discussed in detail. The emerging etching methods including HF etching methods, in situ HF-forming etching methods, electrochemical etching methods, alkali etching methods, and molten salt etching methods, as well as delamination strategies are discussed. Considering the future developments and practical applications, the large-scale synthesis routes and the antioxidation strategies of MXenes are also summarized. In summary, a generalized overview of MXenes synthesis protocols with an outlook for the current challenges and promising technologies for large-scale preparation and stable storage is provided.

Two-dimensional (2D) rare-earth oxides (REO) are a large family of materials with various intriguing applications and the precise facet control is essential for investigating new properties in the 2D limit. However, a bottleneck remains for obtaining their 2D single crystals with specific facets because of the intrinsic non-layered structure and disparate thermodynamic stability of different facets. Herein, for the first time, we achieved the synthesis of a wide variety of high-quality 2D REO single crystals with tailorable facets via designing a hard-soft-acid-base (HSAB) couple for controlling the 2D nucleation of the predetermined facets and adjusting the growth mode and direction of crystals. Also, the facet-related magnetic properties of 2D REO single crystals were revealed. Our approach provides a foundation for further exploring other facet-dependent properties and various applications of 2D REO and an inspiration for the precise growth of other non-layered 2D materials as well.

Boron nitride nanosheets (BNNS) are graphene-like materials with large bandgap and excellent thermal/chemical stability. Current BNNS synthesis methods show low yield and/or purity preventing effective implementation in real-life applications. This work reports two catalyst-free bottom-up approaches for BNNS synthesis using induction thermal plasma. High enthalpy and cooling rates of this plasma allow BNNS to form homogeneously when using solid ammonia borane (AB) as a precursor. In this case, clusters of B x N y H z nucleate to form particles of critical sizes on which BNNS propagate while releasing H 2 . Using boron powders instead of AB produces BNNS through a heterogeneous route. In this case, boron undergoes spheroidization while active nitrogen species diffuse on the liquid surface to form boron nitride nanowalls which propagate into BNNS. The operating pressure and nitrogen loading are shown to control BNNS n...

It becomes clear that, in two-dimensional (2D) materials-based devices, sheet resistances underneath electrodes change due to a metallic contact, leading to substantial errors in determining a transfer length. Thus, the extraction of transfer length and corresponding contact resistivity must be revisited to assess the performance of 2D devices. In this study, we present the three different approaches of determining the contact resistivity in 2D WSe 2 field effect transistors for the first time by theoretical analysis using the resistive network model as well as electrical measurements using the contact-end resistance and transfer length methods, based on the followings: (a) contact resistance multiplied by transfer length ( ##IMG## [http://ej.iop.org/images/2053-1583/8/4/045019/tdmac1adbieqn1.gif] {${R_{{\text{cf}}}}W \cdot {L_{{\text{Tk}}}}$} ), (b) integrated contact resistance ( ##IMG## {$\smallint\limits_0^L R \left( x \right) \cd...}

FePSe₃ atomic layers bolometers present an excellent thermal infrared radiation detection with responsivity and specific detectivity exceeding ≈1 × 10⁸ V W⁻¹ and ≈1 × 10⁹ Jones under 1550 nm short-wave infrared illumination at room temperature, which is on par with the current state-of-the-art conventional bolometers that require suspended structure for thermal isolation and hence improved signal-to-noise ratios.

Abstract

The semiconducting metal phosphorus trichalcogenides (MPX₃, X = S, Se), a new family of layered atomic materials similar to the transition-metal dichalcogenides, have recently attracted great attention owing to their 2D magnetic properties as well as their wide range of tunable bandgaps, which can lead to promising applications in spintronic and optoelectronic devices. Herein, an uncooled bolometer based on FePSe₃ atomic layers is reported, on which a competitive temperature coefficient of resistance (TCR) of ≈−2.96% K⁻¹ at room temperature is observed. In detecting infrared radiation (980–1550 nm) at room temperature using the FePSe₃ bolometer, high responsivity exceeding 10⁸ V W⁻¹ and specific detectivity up to 10⁹ Jones are achieved, which can be attributed to the combined advantages of the competitive room-temperature TCR and natural thermal isolation between the inner layers of FePSe₃ and the environment. This result reveals a remarkable property of FePSe₃ atomic layers and paves the way toward new types of bolometers with high sensitivities.

Author(s): G. Fabiani, M. D. Bouman, and J. H. Mentink

We investigate the propagation of magnons after ultrashort perturbations of the exchange interaction in the prototype two-dimensional Heisenberg antiferromagnet. Using the recently proposed neural quantum states, we predict highly anisotropic spreading in space constrained by the symmetry of the per...

[Phys. Rev. Lett. 127, 097202] Published Wed Aug 25, 2021

Nature, Published online: 25 August 2021; doi:10.1038/s41586-021-03595-z

Unusual width of the superconducting transition in a hydride

Nature, Published online: 25 August 2021; doi:10.1038/s41586-021-03753-3

Restricting the initial growth temperatures used for chemical vapour deposition of graphene on metal foils produces optimum conditions for growing large areas of fold-free, single-crystal graphene.

A lead-free halide perovskite Cs₃Bi₂I₉ single-crystalline thin film, with adjustable thickness and millimeter size, is directly integrated on various substrates including Si wafer, through a supersaturation-controlled method. Benefiting from the incommensurate lattice match and suitable thinness, this silicon-compatible perovskite photodetector is superior to most reported state-of-the-art lead-free halide perovskite photodetectors.

Abstract

Monolithical integration of the promising optoelectronic material with mature and inexpensive silicon circuitry contributes to simplifying device geometry, enhancing performance, and expanding new functionalities. Herein, a lead-free halide perovskite Cs₃Bi₂I₉ single-crystalline thin film (SCTF), with thickness ranging from 900 nm to 4.1 µm and aspect ratio up to 1666, is directly integrated on various substrates including Si wafer, through a facile and low-temperature solution-processing method. The growth kinetics of the lead-free halide perovskite SCTF are elucidated by in situ observation, and the solution supersaturation is controlled to reduce the inverse-temperature crystallization nucleation density and elongate the evaporation growth. The excellent lattice match and band alignment between Si(111) and Cs₃Bi₂I₉(001) facets promote photogenerated charge dissociation and extraction, resulting in boosting the photoelectric sensitivity by 10–200 times compared with photodetectors based on other substrates. More importantly, this silicon-compatible perovskite SCTF photodetector exhibits a high switching ratio of 3000 and a fast response of 1.5 µs, which are higher than most reported state-of-the-art lead-free halide perovskite photodetectors. This work not only gives an in-depth understanding of the perovskite precursor solution chemistry, but also demonstrates the great potential of monolithical integration of lead-free halide perovskite SCTF with a silicon wafer for high-performance photodetectors.

Nature Materials, Published online: 25 August 2021; doi:10.1038/s41563-021-01059-3

Centimetre-scale few-layer black phosphorus films have been grown on a mica substrate by pulsed laser deposition. The high crystalline quality and homogeneity of these films are promising for device applications.

Nature Materials, Published online: 25 August 2021; doi:10.1038/s41563-021-01055-7

A substantial spin–orbit interaction is introduced in a purely silicon heterostructure and can be tuned through an applied gate voltage.

Nature Materials, Published online: 26 August 2021; doi:10.1038/s41563-021-01092-2

Using atomic-resolution electron microscopy to observe ion-exchange processes in atomically thin layered and restacked clays, substantially larger ion diffusion constants and moiré effects on ion dynamics are seen.

Nature Materials, Published online: 26 August 2021; doi:10.1038/s41563-021-01084-2

A borophene polymorph with two covalently bonded boron monolayers was synthesized, expanding the physical properties of borophene and filling the gap between monolayer borophene and icosahedron-based bulk boron.

Nature Materials, Published online: 26 August 2021; doi:10.1038/s41563-021-01072-6

Layered clays are of interest for membranes and many other applications but their ion-exchange dynamics remain unexplored in atomically thin materials. Here, using electron microscopy, it is found that the ion diffusion for few-layer two-dimensional clays approaches that of free water and that superlattice cation islands can form in twisted and restacked materials.