Jing Zhang

Nature Communications, Published online: 16 January 2023; doi:10.1038/s41467-022-35569-8

Top-down exfoliation is one of the most promising approaches for the scalable production of 2D materials, but the current techniques are limited by low yield of monolayers. Here, the authors report the exfoliation of graphene and other layered materials via viscous-polymer-assisted ball-milling, leading to a production of graphene products with monolayer percentage up to 97.9% at a yield of 78.3%.

Nature Communications, Published online: 19 January 2023; doi:10.1038/s41467-023-35986-3

Monolayer graphene can support the quantum Hall effect up to room temperature. Here, the authors provide evidence that graphene encapsulated in hexagonal boron nitride realizes a novel transport regime where dissipation in the quantum Hall phase is mediated predominantly by electron-phonon scattering rather than disorder scattering.

Nature Communications, Published online: 19 January 2023; doi:10.1038/s41467-023-35983-6

Chemical vapor deposition (CVD) is a versatile method to synthesize 2D materials, but usually requires high growth temperatures. Here, the authors report a BiOCl-assisted CVD approach to grow 2D nanosheets from 27 different layered and nonlayered materials at temperatures <500 °C, which are compatible with back-end-of-the-line industrial processes.

Nature Physics, Published online: 16 January 2023; doi:10.1038/s41567-022-01894-4

Superconductivity can emerge from a strange-metal state, but the exact relationship between them is unknown. Now, quantitative measurements reveal the dependence of resistivity in the strange metal on the superconducting transition temperature.

Nature Materials, Published online: 16 January 2023; doi:10.1038/s41563-022-01458-0

The authors present evidence suggesting that amorphous Bi2Se3 displays topological properties, signalling a new regime for the pursuit of topological matter.

A superconducting qubit-metamaterial system creates a scalable lattice quantum simulator.

Nature, Published online: 18 January 2023; doi:10.1038/s41586-022-05461-y

A new exchange-bias effect between two different antiferromagnetic layers enables the fabrication of all-antiferromagnetic structures that have a large room-temperature tunnelling magnetoresistance and potential applications for ultrafast memory technologies.

Nature, Published online: 18 January 2023; doi:10.1038/s41586-022-05524-0

Geometric confinement on arbitrary substrates promotes, without epitaxial seeding, the layer-by-layer growth of two-dimensional single-crystal monolayers and bilayers of transition metal dichalcogenides.

Nature, Published online: 18 January 2023; doi:10.1038/s41586-022-05503-5

The direct observation of in-plane charged domain walls in BiFeO3 ferroelectric films a few nanometres thick, their deterministic creation, manipulation and annihilation by applied voltage, as well the demonstration of their memristive functionality is reported.

Nature Electronics, Published online: 16 January 2023; doi:10.1038/s41928-022-00910-y

An acoustoelectric amplifier based on a three-layer heterostructure design could be used to create all-acoustic radiofrequency microsystems.

Nature Electronics, Published online: 16 January 2023; doi:10.1038/s41928-022-00908-6

Three-layer heterostructures consisting of an indium gallium arsenide semiconducting film, a lithium niobate piezoelectric film, and a silicon substrate can be used to create acoustoelectric amplifiers that operate at gigahertz frequencies with large non-reciprocal gain and low noise in continuous operation.

A fabrication protocol is presented that achieves electrically conductive devices from the ambient-reactive 2D antiferromagnetic semiconductor NiI₂. The resulting gate-tunable transistors show band-like electronic transport at cryogenic temperatures, allowing electrical probing of the thickness-dependent multiferroic phase transition temperature of NiI₂ from 59 K (bulk) to 28 K (monolayer).

Abstract

2D magnetic materials hold promise for quantum and spintronic applications. 2D antiferromagnetic materials are of particular interest due to their relative insensitivity to external magnetic fields and higher switching speeds compared to 2D ferromagnets. However, their lack of macroscopic magnetization impedes detection and control of antiferromagnetic order, thus motivating magneto-electrical measurements for these purposes. Additionally, many 2D magnetic materials are ambient-reactive and electrically insulating or highly resistive below their magnetic ordering temperatures, which imposes severe constraints on electronic device fabrication and characterization. Herein, these issues are overcome via a fabrication protocol that achieves electrically conductive devices from the ambient-reactive 2D antiferromagnetic semiconductor NiI₂. The resulting gate-tunable transistors show band-like electronic transport below the antiferromagnetic and multiferroic transition temperatures of NiI₂, revealing a Hall mobility of 15 cm² V⁻¹ s⁻¹ at 1.7 K. These devices also allow direct electrical probing of the thickness-dependent multiferroic phase transition temperature of NiI₂ from 59 K (bulk) to 28 K (monolayer).

This study reviews the current state of III-nitride synthesis on different 2D materials for a variety of flexible applications, meanwhile identifying key advances in this rapidly accelerating field. The focus of this study is to provide guidelines on the exfoliation of epitaxial layers using 2D materials, with the aim of fabricating flexible nitride devices.

Abstract

Group III-nitrides have attracted significant attention in recent years for their wide tunable band-gaps and excellent optoelectronic capabilities, which are advantageous for several applications including light-emitting diodes, lasers, photodetectors, and large-size low-cost power electronic devices. However, conventional epitaxy accompanied by the covalent bond formation renders the transfer of nitride epilayers difficult, thereby limiting the application potential of nitrides in wearable and flexible electronics. Furthermore, interfacial covalent bonds also limit substrate selection and hinder the development of heterogeneous integration between nitrides and other material systems. 2D materials can mitigate these problems significantly. On the one hand, due to the weak van der Waals forces between the layers of 2D materials, influences of lattice mismatch can be avoided to improve crystal quality. On the other hand, delamination and transfer of nitride epilayers can be achieved easily. Therefore, this study focuses on providing comprehensive guidelines regarding the exfoliation of epitaxial layers using 2D materials to provide new design freedoms for nitride devices. Different 2D buffers and release layers have also been discussed. Furthermore, the limitations, promising solutions, future directions, and applicability of this strategy to flexible nitride devices are presented.

Through direct and automated control over the electron beam scan pathway profile in an aberration-corrected scanning transmission electron microscope, metallic 1D–2D edge heterostructures are fabricated with atomic precision in semiconducting MoS₂. This atomic fabrication workflow paves the way for precision controlled atomic fabrication of functional nanomaterials.

Abstract

The ability to deterministically fabricate nanoscale architectures with atomic precision is the central goal of nanotechnology, whereby highly localized changes in the atomic structure can be exploited to control device properties at their fundamental physical limit. Here, an automated, feedback-controlled atomic fabrication method is reported and the formation of 1D–2D heterostructures in MoS₂ is demonstrated through selective transformations along specific crystallographic orientations. The atomic-scale probe of an aberration-corrected scanning transmission electron microscope (STEM) is used, and the shape and symmetry of the scan pathway relative to the sample orientation are controlled. The focused and shaped electron beam is used to reliably create Mo₆S₆ nanowire (MoS-NW) terminated metallic-semiconductor 1D–2D edge structures within a pristine MoS₂ monolayer with atomic precision. From these results, it is found that a triangular beam path aligned along the zig-zag sulfur terminated (ZZS) direction forms stable MoS-NW edge structures with the highest degree of fidelity without resulting in disordering of the surrounding MoS₂ monolayer. Density functional theory (DFT) calculations and ab initio molecular dynamic simulations (AIMD) are used to calculate the energetic barriers for the most stable atomic edge structures and atomic transformation pathways. These discoveries provide an automated method to improve understanding of atomic-scale transformations while opening a pathway toward more precise atomic-scale engineering of materials.

Interfacial Dynamics

In article number 2207835, Hsien-Yi Hsu and co-workers systematically study interfacial dynamics of bandgap funnelling in MA₃Bi₂Cl_9−x I _x perovskites using temperature-dependent transient photoluminescence and electrochemical voltammetric techniques. The photophysical and (photo)electrochemical phenomena of solid–solid and solid–liquid interfaces are therefore confirmed. The importance of this work is to explore the intrinsic and interfacial properties of semiconductor materials for elucidating the correlation between material characterization and device performance.

Novel ice-aided transfer, ice-stamp transfer, and ice cleaning methods, completely free from polymer and solvents, are developed to yield ultrahigh quality and exceptional cleanliness in 2D materials, which will contribute to technological revolutions in 2D materials, and their associated structures and devices.

Abstract

The scalable 2D device fabrication and integration demand either the large-area synthesis or the post-synthesis transfer of 2D layers. While the direct synthesis of 2D materials on most targeted surfaces remains challenging, the transfer approach from the growth substrate onto the targeted surfaces offers an alternative pathway for applications and integrations. However, the current transfer techniques for 2D materials predominantly involve polymers and organic solvents, which are liable to contaminate or deform the ultrasensitive atomic layers. Here, novel ice-aided transfer and ice-stamp transfer methods are developed, in which water (ice) is the only medium in the entire process. In practice, the adhesion between various 2D materials and ice can be well controlled by temperature. Through such controlled adhesion of ice, it is shown that the new transfer methods can yield ultrahigh quality and exceptional cleanliness in transferred 2D flakes and continuous 2D films, and are applicable for a wide range of substrates. Furthermore, beyond transfer, ice can also be used for cleaning the surfaces of 2D materials at higher temperatures. These novel techniques can enable unprecedented ultraclean 2D materials surfaces and performances, and will contribute to the upcoming technological revolutions associated with 2D materials.

A self-intercalated transition metal dichalcogenide Cr_1+δTe₂ is shown to be a unique magnetic semimetal enabling widely tunable k-space Berry curvature near Fermi energy. The door has been opened for probing and tailoring the intertwined Berry curvature physics in real and momentum space in Cr_1+δTe₂ epitaxial thin films and their heterostructures.

Abstract

Magnetic semimetals have increasingly emerged as lucrative platforms hosting spin-based topological phenomena in real and momentum spaces. Cr_{1+ δ} Te₂ is a self-intercalated magnetic transition metal dichalcogenide (TMD), which exhibits topological magnetism and tunable electron filling. While recent studies have explored real-space Berry curvature effects, similar considerations of momentum-space Berry curvature are lacking. Here, the electronic structure and transport properties of epitaxial Cr_{1+ δ} Te₂ thin films are systematically investigated over a range of doping, δ (0.33 – 0.71). Spectroscopic experiments reveal the presence of a characteristic semi-metallic band region, which shows a rigid like energy shift with δ. Transport experiments show that the intrinsic component of the anomalous Hall effect (AHE) is sizable and undergoes a sign flip across δ. Finally, density functional theory calculations establish a link between the doping evolution of the band structure and AHE: the AHE sign flip is shown to emerge from the sign change of the Berry curvature, as the semi-metallic band region crosses the Fermi energy. These findings underscore the increasing relevance of momentum-space Berry curvature in magnetic TMDs and provide a unique platform for intertwining topological physics in real and momentum spaces.

p-Type NbS₂–MoS₂ lateral heterostructures with a high on/off current ratio are synthesized by a one-step metal–organic chemical vapor deposition (MOCVD) method with Nb dopants present in the monolayer MoS₂. The heterostructure provides a platform to explore the instructive interface of substitutional doped TMDC materials and 2D metal–semiconductor heterojunctions, which paves a prospective way to designing innovative nanoscale devices and complementary metal–oxide–semiconductor (CMOS)-like 2D circuits.

Abstract

Monolayer MoS₂ has attracted significant attention owing to its excellent performance as an n-type semiconductor from the transition metal dichalcogenide (TMDC) family. It is however strongly desired to develop controllable synthesis methods for 2D p-type MoS₂, which is crucial for complementary logic applications but remains difficult. In this work, high-quality NbS₂–MoS₂ lateral heterostructures are synthesized by one-step metal–organic chemical vapor deposition (MOCVD) together with monolayer MoS₂ substitutionally doped by Nb, resulting in a p-type doped behavior. The heterojunction shows a p-type transfer characteristic with a high on/off current ratio of ≈10⁴, exceeding previously reported values. The band structure through the NbS₂–MoS₂ heterojunction is investigated by density functional theory (DFT) and quantum transport simulations. This work provides a scalable approach to synthesize substitutionally doped TMDC materials and provides an insight into the interface between 2D metals and semiconductors in lateral heterostructures, which is imperative for the development of next-generation nanoelectronics and highly integrated devices.

Covalent networks of transition metal dichalcogenides (TMDs) represent an efficient strategy to reduce the interflake junction resistance in thin-film devices. This multiscale investigation reveals that the molecular structure of the linker is crucial to control the overall charge-transport mechanisms. This work highlights the great potential of defect engineering for the fabrication of high-performance devices based on covalent TMD networks.

Abstract

Device performance of solution-processed 2D semiconductors in printed electronics has been limited so far by structural defects and high interflake junction resistance. Covalently interconnected networks of transition metal dichalcogenides potentially represent an efficient strategy to overcome both limitations simultaneously. Yet, the charge-transport properties in such systems have not been systematically researched. Here, the charge-transport mechanisms of printed devices based on covalent MoS₂ networks are unveiled via multiscale analysis, comparing the effects of aromatic versus aliphatic dithiolated linkers. Temperature-dependent electrical measurements reveal hopping as the dominant transport mechanism: aliphatic systems lead to 3D variable range hopping, unlike the nearest neighbor hopping observed for aromatic linkers. The novel analysis based on percolation theory attributes the superior performance of devices functionalized with π-conjugated molecules to the improved interflake electronic connectivity and formation of additional percolation paths, as further corroborated by density functional calculations. Valuable guidelines for harnessing the charge-transport properties in MoS₂ devices based on covalent networks are provided.

Harsh-environment-resistant MoS₂ field-effect transistors are demonstrated by engineering the electrode–channel interfaces with an all-transfer technique of van der Waals electrodes. The intact and defect-free interfaces not only reduce the Schottky barrier height at electrodes, but enable high resistances of the MoS₂ devices to humid, oxidizing, and high-temperature environments, surpassing the devices with other kinds of electrodes.

Abstract

Nanoscale electronic devices that can work in harsh environments are in high demand for wearable, automotive, and aerospace electronics. Clean and defect-free interfaces are of vital importance for building nanoscale harsh-environment-resistant devices. However, current nanoscale devices are subject to failure in these environments, especially at defective electrode–channel interfaces. Here, harsh-environment-resistant MoS₂ transistors are developed by engineering electrode–channel interfaces with an all-transfer of van der Waals electrodes. The delivered defect-free, graphene-buffered electrodes keep the electrode–channel interfaces intact and robust. As a result, the as-fabricated MoS₂ devices have reduced Schottky barrier heights, leading to a very large on-state current and high carrier mobility. More importantly, the defect-free, hydrophobic graphene buffer layer prevents metal diffusion from the electrodes to MoS₂ and the intercalation of water molecules at the electrode–MoS₂ interfaces. This enables high resistances of MoS₂ devices with all-transfer electrodes to various harsh environments, including humid, oxidizing, and high-temperature environments, surpassing the devices with other kinds of electrodes. The work deepens the understanding of the roles of electrode–channel interfaces in nanoscale devices and provides a promising interface engineering strategy to build nanoscale harsh-environment-resistant devices.

Nature Nanotechnology, Published online: 16 January 2023; doi:10.1038/s41565-022-01309-8

Electrons in two-dimensional semiconductor moiré materials experience competing magnetic interactions. Magneto-optical measurements of moiré devices with controlled screening of the Coulomb interactions now evidence a Wigner–Mott insulating state with frustrated magnetic interactions.

Nature Nanotechnology, Published online: 16 January 2023; doi:10.1038/s41565-022-01308-9

Modulating the interaction of a thin film with microwaves is realized using the electrochemical behaviours of various MXenes.

Nature Materials, Published online: 12 January 2023; doi:10.1038/s41563-022-01454-4

The realization of strongly correlated bosons in a solid-state lattice is challenging. Here, the authors trap interlayer excitons in an angle-aligned WS2/bilayer WSe2/WS2 multilayer moiré lattice and observe correlated insulating states.

Determination of crystal structures of nanocrystalline compounds is a great challenge in solid-state chemistry. In this work, an algorithm is introduced, which is able to determine the crystal structure of an unknown compound by means of an on-the-fly trained machine learning model that combines density functional calculations with comparison of calculated and measured pair distribution functions for global optimization.

Abstract

Determination of crystal structures of nanocrystalline or amorphous compounds is a great challenge in solid-state chemistry and physics. Pair distribution function (PDF) analysis of X-ray or neutron total scattering data has proven to be a key element in tackling this challenge. However, in most cases, a reliable structural motif is needed as a starting configuration for structure refinements. Here, an algorithm that is able to determine the crystal structure of an unknown compound by means of an on-the-fly trained machine learning model, which combines density functional theory calculations with comparison of calculated and measured PDFs for global optimization in an artificial landscape, is presented. Due to the nature of this landscape, even metastable configurations and stacking disorders can be identified.