Jiuxiang Dai

An on-surface reaction strategy is developed to integrate radicals with protective umbrellas on 2D layered material surfaces to construct stable and ordered radicals. For example, triethylamine reacts with dichloromethane to form quaternary ammonium salts with further Hofmann elimination to produce diethylmethyleneamine (DEMA) radicals, reacting with black phosphorus (BP) to produce P radicals with DEMA protective umbrellas integrated on BP surface.

Abstract

Radicals are closely related to human life and health and have been widely used in biology, chemistry, functional materials, etc. However, the high reactivity, disorder, and short half-lives limit their wide applications. Therefore, it remains a great challenge to prepare stable and ordered radicals. Herein, radicals are prepared with protective umbrellas (diethylmethyleneamine, DEMA) that are integrated on the surface of 2D layered materials to isolate water and oxygen and enhance the stability of radicals. Taking 2D black phosphorus (BP) as an example: triethylamine reacts with dichloromethane to form quaternary ammonium salts with further Hoffmann elimination to produce DEMA radicals that could react with one electron of a lone pair electrons in P on the surface of BP to produce P radicals, which shows a prolonged half-life of 21 days at room temperature. First-principle calculations and electron paramagnetic resonance fitting confirm that the steric hindrance constructed by dense DEMA passivation layer acts as a protective umbrella and the 2D coupling of P radicals and other P atoms in 2D BP plane to enhance the stability and strong superexchange interaction of P radicals. Furthermore, it is a general strategy to produce stable radicals integrated on the 2D plane.

Interlayer vibrational modes in 2H-MoTe 2 /hBN heterostructures were investigated by low-frequency Raman spectroscopy. A series of low-frequency Raman modes are observed for MoTe 2 thicknesses of 1–4 layers: the shear modes of MoTe 2 persist in the heterostructure with no shift in the frequency, but the breathing modes show dramatic changes in the heterostructures. The number and the frequencies of the breathing modes do not depend on the twist angle between the two materials but strongly vary with the layer thicknesses of both MoTe 2 and hBN layers. The breathing modes were observed for both resonant (1.96 eV) and non-resonant (2.41 eV) excitations. The breathing mode frequencies were analyzed by using the linear chain model, and the interfacial force constant between 2 H-MoTe 2 and hBN is estimated to be 3.77 × 10 19 N m −3 .

In this work, we investigate the role of substrates in determining the morphologies and electronic structures of two-dimensional (2D) Sn. We use Ir(111) and 2D hexagonal boron nitride (h-BN) predeposited on Ir(111) as substrates. The latter contains Moiré patterns with varying binding strength between h-BN and metal. Using scanning tunneling microscopy and first-principles calculations, we reveal the distinct morphologies of 2D Sn on different substrates. Of particular interest, we discover a new √7 × √7 Sn phase, originating from the local charge transfer with metal beneath the ‘decoupling’ h-BN monolayer at the strongly interacting Moiré region. To the best of our knowledge, this work demonstrates, for the first time via combined experimental and theoretical approach, that new 2D Sn phases can be achieved using Moiré patterns on h-BN/metal. This finding should be instrumental in the development of 2D-based topological materials.

Nature Materials, Published online: 22 July 2021; doi:10.1038/s41563-021-01053-9

Superionic conductors present liquid-like ionic diffusivity with applications ranging from energy storage to thermoelectrics. A two-dimensional type I superionic conductor α-KAg3Se2 is now reported and should help to design other materials with tailored ionic conductivities and phase transitions.

Wafer-scale growth of single-grain 2D metal chalcogenides remains a challenge in the commercialization of various electronic devices based on these materials. A generalized surface-diffusion-induced epitaxial self-planarization method to produce wafer-scale single-grain metal chalcogenide thin films is described. This process also enables the practical applications of single-grain metal chalcogenides without involving a transfer process.

Abstract

Although wafer-scale single-grain thin films of 2D metal chalcogenides (MCs) have been extensively sought after during the last decade, the grain size of the MC thin films is still limited in the sub-millimeter scale. A general strategy of synthesizing wafer-scale single-grain MC thin films by using commercial wafers (Si, Ge, GaAs) both as metal source and epitaxial collimator is presented. A new mechanism of single-grain thin-film formation, surface diffusion, and epitaxial self-planarization is proposed, where chalcogen elements migrate preferentially along substrate surface and the epitaxial crystal domains flow to form an atomically smooth thin film. Through synchrotron X-ray diffraction and high-resolution scanning transmission electron microscopy, the formation of single-grain Si₂Te₃, GeTe, GeSe, and GaTe thin films on (111) Si, Ge, and (100) GaAs is verified. The Si₂Te₃ thin film is used to achieve transfer-free fabrication of a high-performance bipolar memristive electrical-switching device.

npj 2D Materials and Applications, Published online: 22 July 2021; doi:10.1038/s41699-021-00247-8

Photocatalytic activity of twist-angle stacked 2D TaS₂

A Janus wound dressing is reported to unidirectionally remove the excessive biofluid and promote wound healing. The result indicates that the Janus PDMS film is suitable for potential applications on the stretched or bent skin surface. This study is valuable for designing and fabricating next-generation dressings with high performance for clinical applications.

Abstract

The intrinsic hydrophilicity of conventional dressings cannot achieve effective management of excessive biofluid around the wound bed, which inevitably causes infection and hinders wound healing. In addition, present dressings such as medical gauze or band aids have a limited stretching capability, which does not comply well with the skin deformation during muscle movement, thus impacting patient comfort. Herein, a Janus wound dressing is reported by assembling an external hydrophobic (HP) adhesive tape, a filter paper, and a polydimethylsiloxane (PDMS) Janus film. The PDMS Janus film as the primary dressing can unidirectionally remove biofluid away from the wound bed. The mechanism of the unidirectional biofluid transport is investigated, demonstrating that the stretching or bending of the Janus dressing is beneficial for unidirectional biofluid draining. It indicates that the Janus PDMS film has potential for practical applications on stretched or bended skin surface. In addition, in order to prevent bacterial infection, amoxicillin powder is uniformly encapsulated on the HP layer of Janus film, resulting in faster wound healing. This study is valuable for designing and fabricating next-generation dressings with high performance for clinical applications.

2D van der Waals heterojunctions (vdWh) are a novel type of metamaterial developed rapidly in recent years. It has been widely used in the research of improving the performance of nanophotonic devices. This review summarizes the fabrication methods of 2D vdWhs and the research progress of nanophotonic devices based on 2D vdWhs. The critical challenges and future perspectives are discussed.

Abstract

2D van der Waals heterojunctions (vdWhs) are a novel type of metamaterial that are flexible, adjustable, and easy to assemble. Using weak van der Waals forces (vdWfs), layered 2D materials can stack freely to form vdWhs with atomic level flat interfaces. By using different 2D materials and specific stacking methods, their unique properties can be organically combined, to exhibit more abundant optical properties. In fact, nanophotonic devices based on 2D vdWhs have developed rapidly and made significant progress. Therefore, the main progress of 2D vdWhs nanophotonic devices in recent years, including the preparation methods of 2D vdWhs and the performance improvements of various nanophotonic devices, is reviewed. Lastly, the prospects of 2D vdWhs nanophotonic devices are discussed.

Two-dimensional organic-inorganic materials have been unable to break the bottleneck of photocurrent generation without external bias due to their poor electrical properties. In article number 2100564, Chun-Wei Chen, Kazuhito Tsukagoshi, Hiroshi Nishihara, and co-workers used liquid/liquid interfacial polymerization to synthesize the bis(dithiolene) iron(II) coordination nanosheet with self-powered UV photoresponse. Moreover, the selfpowered photodetectors maintained 94% of their initial photocurrent after 60 days of aging in air without encapsulation.

Author(s): Chern Chuang and Jianshu Cao

Low-dimensional excitonic materials have inspired much interest owing to their novel physical and technological prospects. In particular, those with strong in-plane anisotropy are among the most intriguing but short of general analyses. We establish the universal functional form of the anisotropic d...

[Phys. Rev. Lett. 127, 047402] Published Wed Jul 21, 2021

Nature, Published online: 21 July 2021; doi:10.1038/s41586-021-03685-y

A large violation of the Pauli limit and re-entrant superconductivity in a magnetic field is reported for magic-angle twisted trilayer graphene, suggesting that the spin configuration of the superconducting state of this material is unlikely to consist of spin singlets.

Nature, Published online: 21 July 2021; doi:10.1038/s41586-021-03679-w

A new type of Hall effect—the layer Hall effect—is produced in a 2D antiferromagnet that does not exhibit any net magnetization.

Nature, Published online: 21 July 2021; doi:10.1038/d41586-021-01890-3

A material system known as magic-angle twisted trilayer graphene exhibits superconductivity. The observation that this superconductivity persists under a strong magnetic field could lead to advances in quantum computation.

Over the last decade, organic-inorganic hybrid perovskites (OIHPs), have developed with great potential for the next-generation electronic and optoelectronic devices. In particular, their excellent properties can be further engineered by chemical compositions, material sizes, device structures, interface modifications, external fields and so on. More recently, dimensionality tuning is found to play a significant role in promoting the properties of OIHPs. Originating from structure diversity and quantum confinement effect, the emerging different forms of perovskites, such as nanocrystals, nanowires/nanorods, nanoplatelets/nanosheets and ultrathin films, have heralded new opportunities for novel physical phenomenon and high-performance devices. Particularly, ultrathin two-dimensional (2D) OIHPs, combing the advantages of 2D morphology and hybrid perovskite component, is a boon for flexible electronic and optoelectronics

Light: Science & Applications, Published online: 20 July 2021; doi:10.1038/s41377-021-00593-8

This review article describes the current state of InN nanostructure and quantum dot growth by metalorganic chemical vapor deposition and the use in optoelectronic applications.

Nature Nanotechnology, Published online: 19 July 2021; doi:10.1038/s41565-021-00936-x

The preparation of a diverse set of 2D materials and their co-integration in van der Waals heterostructures enable innovative material design and device engineering. This Review summarizes recent advances in 2D spintronics and opto-spintronics, the underlying physical concepts and future perspectives of the field.