Jing Zhang

Nature Communications, Published online: 19 December 2022; doi:10.1038/s41467-022-35477-x

In twisted 2D materials, spontaneous lattice reconstructions mean that twist angle alone provides an incomplete description. Here, using electron diffraction, the authors show that the displacement field in twisted bilayer graphene can be described as a superposition of three periodic lattice distortion (PLD) waves with wavevectors oriented at 120° from each other, forming a “torsional" PLD.

Nature Communications, Published online: 19 December 2022; doi:10.1038/s41467-022-35278-2

Detection of cytokine biomarkers has the potential to aid in diagnosis and treatment of different diseases. Here, the authors report on the creation of an asymmetric geometry MoS2 diode-based biosensor for the detection of TNF-α as a model biomarker in a proof of concept study.

Nature Materials, Published online: 19 December 2022; doi:10.1038/s41563-022-01424-w

The authors demonstrate that magnetic proximity interactions in a hexagonal boron nitride-encapsulated MoSe2/CrBr3 van der Waals heterostructure have a striking difference in the two (K, K′) valleys of a monolayer MoSe2.

Nature Electronics, Published online: 19 December 2022; doi:10.1038/s41928-022-00878-9

Floating-gate memristive synaptic devices that are fabricated using commercial complementary metal–oxide–semiconductor processes can be used to create energy-efficient restricted Boltzmann machines and deep belief neural networks.

Nature Electronics, Published online: 20 December 2022; doi:10.1038/s41928-022-00909-5

Technology breakthroughs at the 2022 IEEE International Electron Devices Meeting, where transistors remain centre stage, 75 years after their invention.

A novel strategy to generate and manipulate robust bound states in the continuum (BICs) in a few-layer tungsten disulfide (WS₂) integrated photonic crystal slab is theoretically demonstrated in article number 2201634 by Chen Zhao and co-workers. The surrounding eight isolated BICs in momentum space move towards the center with electrically tuning the carrier density in few-layer WS₂. BICs with opposite topological charge annihilate in the merging process to achieve a high quality factor in a large area at the center.

Recently, emerging 2D materials such as graphene, hexagonal boron nitride, and transition metal dichalcogenides have attracted considerable research attention because of their outstanding electrical, optical, and mechanical properties, which are ideal for flexible electronics. The recent progress and challenges of 2D material growth and display applications are reviewed and perspectives for exploring 2D materials for display applications are discussed.

Abstract

With advances in flexible electronics, innovative foldable, rollable, and stretchable displays have been developed to maintain their performance under various deformations. These flexible devices can develop more innovative designs than conventional devices due to their light weight, high space efficiency, and practical convenience. However, developing flexible devices requires material innovation because the devices must be flexible and exhibit desirable electrical insulating/semiconducting/metallic properties. Recently, emerging 2D materials such as graphene, hexagonal boron nitride, and transition metal dichalcogenides have attracted considerable research attention because of their outstanding electrical, optical, and mechanical properties, which are ideal for flexible electronics. The recent progress and challenges of 2D material growth and display applications are reviewed and perspectives for exploring 2D materials for display applications are discussed.

This work provides an overview of passive flame-retardant materials and next-generation smart fire warning materials/sensors based on MXene and its derivatives, including their conceptual design, characterization, modification principles, performances, applications, mechanisms, challenges, and future perspectives.

Abstract

Frequent fire disasters have caused massive impacts to the environment, human beings, and the economy. MXene has recently been intensively researched as potential flame retardants to provide passive fire protection for other materials via its physical barrier and catalyzing carbonization effects. In parallel, MXene has also demonstrated a great promise for creating early fire warning sensors, which is an emerging field that has the potential to provide active fire response through its thermoelectric effect. This makes it possible to integrate passive fire retardancy and active fire warning into one MXene-based fire protection system on demand. However, fulfilling these promises needs more research. Herein, an overview of passive flame-retardant materials and next-generation smart fire warning materials/sensors based on MXene and its derivatives is provided. This study reviews their conceptual design, characterization, modification principles, performances, applications, and mechanisms. A discussion of the challenges that need to be solved for their future practical applications and opportunities is also presented.

Controlling and tuning the orbital ordering in a single molecule using a monolayer ferroelectric substrate is realized. This is achieved by adsorbing transition metal phthalocyanine (TMPc) molecules on a ferroelectric monolayer SnTe. The orbital order is probed using low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy experiments, and it is demonstrated that it can be controllably changed by switching the polarization direction of the underlying ferroelectric monolayer.

Abstract

2D ferroelectric materials provide a promising platform for the electrical control of quantum states. In particular, due to their 2D nature, they are suitable for influencing the quantum states of deposited molecules via the proximity effect. Here, electrically controllable molecular states in phthalocyanine molecules adsorbed on monolayer ferroelectric material SnTe are reported. The strain and ferroelectric order in SnTe are found to create a transition between two distinct orbital orders in the adsorbed phthalocyanine molecules. By controlling the polarization of the ferroelectric domain using scanning tunneling microscopy (STM), it is successfully demonstrated that orbital order can be manipulated electrically. The results show how ferroelastic coupling in 2D systems allows for control of molecular states, providing a starting point for ferroelectrically switchable molecular orbital ordering and ultimately, electrical control of molecular magnetism.

The horizontal mirror symmetry in BaAgSb vanishes the electron–phonon coupling mediated by phonons with purely out-of-plane vibrational vectors, which weakens the phonon-induced carrier scattering and triggers a record hole mobility among polycrystalline quasi-2D thermoelectrics. Such high mobility accompanied with intrinsically low thermal conductivity gives rise to excellent p-type thermoelectric performance in polycrystalline BaAgSb.

Abstract

Quasi-2D semiconductors have garnered immense research interest for next-generation electronics and thermoelectrics due to their unique structural, mechanical, and transport properties. However, most quasi-2D semiconductors experimentally synthesized so far have relatively low carrier mobility, preventing the achievement of exceptional power output. To break through this obstacle, a route is proposed based on the crystal symmetry arguments to facilitate the charge transport of quasi-2D semiconductors, in which the horizontal mirror symmetry is found to vanish the electron–phonon coupling strength mediated by phonons with purely out-of-plane vibrational vectors. This is demonstrated in ZrBeSi-type quasi-2D systems, where the representative sample Ba_1.01AgSb shows a high room-temperature hole mobility of 344 cm² V⁻¹ S⁻¹, a record value among quasi-2D polycrystalline thermoelectrics. Accompanied by intrinsically low thermal conductivity, an excellent p-type zT of ≈1.3 is reached at 1012 K, which is the highest value in ZrBeSi-type compounds. This work uncovers the relation between electron–phonon coupling and crystal symmetry in quasi-2D systems, which broadens the horizon to develop high mobility semiconductors for electronic and energy conversion applications.

Nature Communications, Published online: 15 December 2022; doi:10.1038/s41467-022-34812-6

One particularly useful feature of van der Waals materials is the ability to combine layers of different materials into a single heterostructure, which can have superior properties than any of the constituent materials alone. Here, Cheng et al. combine two interlayer-antiferromagnetic chromium trihalides, CrI3 and CrCl3 in close proximity, and demonstrate ferromagnetic coupling between them.

Nature Materials, Published online: 14 December 2022; doi:10.1038/s41563-022-01445-5

A combination of tunnelling spectroscopy, magnetotransport, electron diffraction and ab initio calculations have revealed that picometre-scale lattice distortions reverse magnetic anisotropy and enhance magnetic frustration in atomically thin ruthenium trichloride — a key step towards realizing a quantum spin liquid in the two-dimensional limit.

Nature Materials, Published online: 15 December 2022; doi:10.1038/s41563-022-01444-6

Thermal Hall conductivity originating from topological magnons is observed in the Kitaev candidate α-RuCl3 in broad intervals of temperature and in-plane magnetic field, raising questions on the role of the Majorana mode in heat conduction.

Nature, Published online: 14 December 2022; doi:10.1038/s41586-022-05382-w

Valentini et al. devise a method through which they can perform both tunnelling spectroscopy and Coulomb blockade spectroscopy on the same hybrid nanowire island to reduce ambiguities in the detection of Majorana.

Nature Communications, Published online: 13 December 2022; doi:10.1038/s41467-022-35339-6

Layer dependence is an important aspect to properties of van der Waals materials. Here, the authors obtain layer dependent multiple polarization states in 3 R MoS2 and propose a generalized model to describe their ferroelectric switching processes.

Nature Electronics, Published online: 12 December 2022; doi:10.1038/s41928-022-00899-4

Two-dimensional semiconductors can be used as a channel material in gate-all-around nanosheet field-effect transistors.

Nature Electronics, Published online: 12 December 2022; doi:10.1038/s41928-022-00882-z

The magnetic anisotropy of the van der Waals ferromagnet Fe5GeTe2 can be continuously tuned—from an initial out-of-plane orientation to a canted orientation and then finally to an in-plane orientation—using electrical gating.

Nature Nanotechnology, Published online: 12 December 2022; doi:10.1038/s41565-022-01257-3

A chemical-vapour-deposition-based approach enables the phase-controllable synthesis of large-scale two-dimensional β-, β′- and α-In2Se3 films.

Nature Nanotechnology, Published online: 12 December 2022; doi:10.1038/s41565-022-01263-5

Manipulation of vacancy and strain enables fabrication of large area, phase-controllable 2D ferroelectric materials and their hetero-phase junction.

Equilateral triangle-shaped graphene nanoislands with a lateral dimension of n benzene rings are known as triangulenes. Individual triangulenes are open-shell molecules, with single-particle electronic spectra that host n − 1 half-filled zero modes and a many-body ground state with spin . The on-surface synthesis of triangulenes has been demonstrated for and the observation of a Haldane symmetry-protected topological phase has been reported in chains of [3]triangulenes. Here, we provide a unified theory for the electronic properties of a family of two-dimensional honeycomb lattices whose unit cell contains a pair of triangulenes with dimensions . Combining density functional theory and tight-binding calculations, we find a wealth of half-filled narrow bands, including a graphene-like spectrum (for ), spin-1 Dirac electrons (for ), -orbital physics (for ), as well as a gapped system with flat valence and conduction bands (for ). All these results are rationalized with a class of effective Hamiltonians acting on the subspace of the zero-energy states that generalize the graphene honeycomb model to the case of fermions with an internal pseudospin degree of freedom with C3 symmetry.

High-symmetry WSe₂ is endowed with anisotropic physical property through van der Waals (vdW) interlayer coupling engineering. In the photodetection test, the polarization angle of the incident light shows significant difference between 0° and 90°, indicating that the WSe₂/CrOCl heterostructure has linear dichroic photodetection behavior.

Abstract

Driven by the unique linear dichroism feature of anisotropic two-dimensional (2D) materials, much attempt has been made to introduce artificial anisotropy into isotropic 2D materials to deliver polarization-sensitive performance. However, those methods have not been widely promoted because of technical limitations. This paper reports on the successful modulation to the structural symmetry of WSe₂ through van der Waals (vdW) interlayer coupling. Correspondingly, both the polarized Raman and photoluminescence (PL) spectra of WSe₂ in heterostructure exhibit periodic variation tendency. Similarly, direction-sensitive electronic transport has also been observed in WSe₂/CrOCl heterostructure, and the conductance along armchair direction is ≈1.5 times of that along zigzag direction. As a functional illustration to the interlayer coupling induced linear dichroism, angle-dependent photodetection is conducted to WSe₂/CrOCl device. With light irradiation at 532 nm, the device photocurrent along armchair direction is 1.27 times higher than that along zigzag direction. The abnormal linear dichroism of WSe₂ in the study clearly proves that few-layer WSe₂ on CrOCl flake has been entitled with artificial anisotropy. The interlayer coupling method is feasible and practical in 2D-material range, offering the possibility to develop polarization-dependent electronic, pyroelectric, and photoelectric devices from isotropic 2D materials.

Recent developments in hafnia-based ferroelectric materials and their applications are comprehensively reviewed, with an in-depth analysis of ferroelectric transistors and their array structures. The relevant technological issues and their solutions are also discussed. This review provides a roadmap for the development of high-performance ferroelectric memory and neuromorphic devices based on ferroelectric transistors.

Abstract

Ferroelectric materials have been intensively investigated for high-performance nonvolatile memory devices in the past decades, owing to their nonvolatile polarization characteristics. Ferroelectric memory devices are expected to exhibit lower power consumption and higher speed than conventional memory devices. However, non-complementary metal–oxide–semiconductor (CMOS) compatibility and degradation due to fatigue of traditional perovskite-based ferroelectric materials have hindered the development of high-density and high-performance ferroelectric memories in the past. The recently developed hafnia-based ferroelectric materials have attracted immense attention in the development of advanced semiconductor devices. Because hafnia is typically used in CMOS processes, it can be directly incorporated into current semiconductor technologies. Additionally, hafnia-based ferroelectrics show high scalability and large coercive fields that are advantageous for high-density memory devices. This review summarizes the recent developments in ferroelectric devices, especially ferroelectric transistors, for next-generation memory and neuromorphic applications. First, the types of ferroelectric memories and their operation mechanisms are reviewed. Then, issues limiting the realization of high-performance ferroelectric transistors and possible solutions are discussed. The experimental demonstration of ferroelectric transistor arrays, including 3D ferroelectric NAND and its operation characteristics, are also reviewed. Finally, challenges and strategies toward the development of next-generation memory and neuromorphic applications based on ferroelectric transistors are outlined.