Jing Zhang

Nature, Published online: 27 April 2022; doi:10.1038/s41586-022-04504-8

A Josephson diode is made by fabricating an inversion symmetry breaking van der Waals heterostructure of NbSe2/Nb3Br8/NbSe2, demonstrating that even without a magnetic field, the junction can be superconducting with a positive current but resistive with a negative current.

Nature Electronics, Published online: 25 April 2022; doi:10.1038/s41928-022-00756-4

Thin flakes of Cr5Te8, which exhibit a colossal anomalous Hall effect, can be synthesized using a phase-controlled chemical vapour deposition technique.

Nature Electronics, Published online: 25 April 2022; doi:10.1038/s41928-022-00757-3

A van der Waals integration approach can be used to deposit single-crystal strontium titanate on two-dimensional molybdenum disulfide and tungsten diselenide, creating high-performance n- and p-doped field-effect transistors.

Nature Electronics, Published online: 27 April 2022; doi:10.1038/s41928-022-00771-5

Author Correction: Transistor qubits heat up

Nature Electronics, Published online: 28 April 2022; doi:10.1038/s41928-022-00761-7

Room-temperature skyrmions in 2D ferromagnets

Nature Electronics, Published online: 28 April 2022; doi:10.1038/s41928-022-00759-1

Graphene on edge

Nature, Published online: 27 April 2022; doi:10.1038/s41586-022-04512-8

A study combining spectroscopy and mathematical topology reports the observation of linked node loops in a quantum magnet, with properties suggesting a Seifert bulk–boundary correspondence.

Advanced Functional Materials, Volume 32, Issue 17, April 25, 2022.

Electrostatic interactions at ferroelectric van der Waals (vdW) heterostructures are intertwined by polarization bound charges and trapped space charges. In MoS₂/CuInP₂S₆ heterostructure, complementary microscopic imaging techniques reveal that charge injection during polarization switching plays a dominant role in modulating the photoluminescent properties of MoS₂ instead of ferroelectric polarization, highlighting the importance of extrinsic charge field effect on vdW devices.

Abstract

Ferroelectric van der Waals (vdW) heterostructure have recently emerged as a low-power, versatile device paradigm because it combines the great diversity of the 2D materials and the memory nature of ferroelectrics. The non-volatile field effect generated by the polarization bound charge is the pivotal factor for the device's performance. Unfortunately, microscopic studies on the interplay between polarization switching and electrostatic coupling at the heterojunction remain largely overlooked. Herein, the authors investigate the electrostatic coupling phenomena of vdW heterostructures consisting of semiconducting MoS₂ and ferroelectric CuInP₂S₆. Significant charge injection accompanying the polarization reversal appears to be the governing field effect that modulates the electronic and photoluminescent properties of MoS₂, as revealed by correlated ferroelectric domain, surface potential, and photoluminescence microscopies. Conversely, the photoactivity of the MoS₂ also affects the polarization stability of CuInP₂S₆. This work provides direct microscopic insight into the mutual electrostatic interactions in vdW ferroelectric-semiconductor heterojunctions, which has broad implications for ferroelectric field-effect applications.

The plasmon in MXene plays a role in the electromagnetic absorption, but such an effect has not yet been quantitatively analyzed due to the lack of knowledge of the MXene's plasmon dispersion, which is challengeable to measure for optical methods. The plasmon dispersions for individual MXene nanoflakes with varied thicknesses are measured using high-spatial-resolution electron energy-loss spectroscopy.

Abstract

2D metal carbides and nitrides (MXene) are promising candidates for electromagnetic (EM) shielding, saturable absorption, thermal therapy, and photocatalysis owing to their excellent EM absorption. The plasmon resonances in metallic MXene micro/nanostructures may play an important role in enhancing the EM absorption; however, their contribution has not been determined due to the lack of a precise understanding of its plasmon behavior. Here, the use of high-spatial-resolution electron energy-loss spectroscopy to measure the plasmon dispersion of MXene films with different thicknesses is reported, enabling accurate analysis of the EM absorption of complex MXene structures in a wide frequency range via a theoretical model. The EM absorption of MXene can be excited at the desired frequency by controlling the momentum (e.g., the sizes of the nanoflakes for EM excitation) as the strength can be enhanced by increasing the layer number and the interlayer distance in MXene. For example, a 3 nm interlayer distance can nearly double the plasmon-enhanced EM absorption in MXene nanostructures. These findings can guide the design of advanced ultrathin EM absorption materials for a broad range of applications.

A van der Waals exfoliation (vdWE) method to fabricate ultrathin films down to the thickness of effective piezoelectric domains is presented. The vdWE method facilitates the detection of piezoelectricity and make the application of piezoelectric biological tissues possible. The vdWE-processed SIS (small intestinal submucosa) ultrathin film reaches the thickness of 100 nm and exhibits enhanced piezoelectricity.

Abstract

Piezoelectric biomaterials have attracted significant attention due to the potential effect of piezoelectricity on biological tissues and their versatile applications. However, the high cost and complexity of assembling and domain aligning biomolecules at a large scale, and the disordered arrangement of piezoelectric domains as well as the lack of ferroelectricity in natural biological tissues remain a roadblock toward practical applications. Here, utilizing the weak van der Waals interaction in the layered structure of small intestinal submucosa (SIS), a van der Waals exfoliation (vdWE) process is reported to fabricate ultrathin films down to the thickness of the effective piezoelectric domain. Based on that, the piezoelectric property is revealed of SIS stemming from the collagen fibril, with piezoelectric coefficients up to 4.1 pm V⁻¹ and in-plane polarization orientation parallel to the fibril axis. Furthermore, a biosensor based on the vdWE-processed SIS film with an in-plane electrode is demonstrated that produces open-circuit voltages of ≈250 mV under the cantilever vibration condition. The vdWE method shows great potential in facilely fabricating ultrathin films of soft tissues and biosensors.

A design strategy, namely “dual self-built gating” is reported to boost the hydrogen evolution reaction. Taking ReS₂ and WS₂ as an example, dual self-built gating induces electrons from WS₂ to ReS₂ directionally. The tailored electronic structure can balance the adsorption of intermediates and the desorption of hydrogen synergistically, thus greatly promoting the intrinsic activity of the active sites.

Abstract

Optimizing the intrinsic activity of active sites is an appealing strategy for accelerating the kinetics of the catalytic process. Here, a design principle, namely “dual self-built gating”, is proposed to tailor the electronic structures of catalysts. Catalytic improvement is confirmed in a model catalyst with a ReS₂–WS₂/WS₂ hybridized heterostructure. As demonstrated in experimental and theoretical results, the dual gating can bidirectionally guide electron transfer and redistribute at the interface, endowing the model catalyst with an electron-rich region. The tailored electronic structures balance the adsorption of intermediates and the desorption of hydrogen synergistically to enhance the reaction kinetics for the hydrogen evolution reaction. Interestingly, the effect of dual gating can be easily amplified by the electric field. The overpotential and Tafel slope (49 mV, 35 mV dec⁻¹) obtained under the electric field for ReS₂–WS₂/WS₂ catalyst with the dual self-built gating effect are far below than those (210 mV, 116 mV dec⁻¹) of the pure WS₂ catalyst, which exhibits nearly four times improvement. The concept of dual gating can be applied to more systems, offering a new guideline for designing advanced electrocatalysts.

Defects open a new ultrafast interlayer electron–phonon coupling in WS₂/graphene heterostructures, which involves a three-body collision between electrons in WS₂ and both acoustic phonons and defects in graphene. This ultrafast process is directly visualized by femtosecond transient absorption microscopy. Through controlling the defect density in graphene, the interlayer electron–phonon scattering time ranges from 7.1 to 2.4 ps.

Abstract

Engineering ultrafast interlayer coupling provides access to new quantum phenomena and novel device functionalities in atomically thin van der Waals heterostructures. However, due to all the atoms of a monolayer material being exposed at the interfaces, the interlayer coupling is extremely susceptible to defects, resulting in high energy dissipation through heat and low device performance. The study of how defects affect the interlayer coupling at ultrafast and atomic scales remains a challenge. Here, using femtosecond transient absorption microscopy, a new defect-induced ultrafast interlayer electron–phonon coupling pathway is identified in a WS₂/graphene heterostructure, involving a three-body collision between electrons in WS₂ and both acoustic phonons and defects in graphene. This interaction manifests as the reduced defect-related Raman resonant activity and the accelerated electron–phonon scattering time from 7.1 to 2.4 ps. Furthermore, the ultrafast interlayer coupling process is directly imaged. These insights will advance the fundamental knowledge of heat dissipation in nanoscale devices, and enable new ways to dynamically manipulate electrons and phonons via defects in van der Waals heterostructures.

The effect of biaxial strain and layer numbers of MoS₂ nanoshells on the electrocatalytic activity is investigated in detail. Calculations reveal the superiority of biaxial strain over uniaxial strain and identify the ideal Mo coordination and S vacancies for maximal catalytic activity.

Abstract

Strain in layered transition-metal dichalcogenides (TMDs) is a type of effective approach to enhance the catalytic performance by activating their inert basal plane. However, compared with traditional uniaxial strain, the influence of biaxial strain and the TMD layer number on the local electronic configuration remains unexplored. Herein, via a new in situ self-vulcanization strategy, biaxially strained MoS₂ nanoshells in the form of a single-crystalline Ni₃S₂@MoS₂ core–shell heterostructure are realized, where the MoS₂ layer is precisely controlled between the 1 and 5 layers. In particular, an electrode with the bilayer MoS₂ nanoshells shows a remarkable hydrogen evolution reaction activity with a small overpotential of 78.1 mV at 10 mA cm^-2, and negligible activity degradation after durability testing. Density functional theory calculations reveal the contribution of the optimized biaxial strain together with the induced sulfur vacancies and identify the origin of superior catalytic sites in these biaxially strained MoS₂ nanoshells. This work highlights the importance of the atomic-scale layer number and multiaxial strain in unlocking the potential of 2D TMD electrocatalysts.

Nature Electronics, Published online: 25 April 2022; doi:10.1038/s41928-022-00753-7

High-performance n-type molybdenum disulfide and p-type tungsten diselenide field-effect transistors can be fabricated using single-crystal strontium titanate dielectrics that are transferred onto two-dimensional semiconductors with the help of van der Waals forces.

2D layered materials, exhibiting exotic structural, electrical, and magnetic properties, provide a superior platform for implementing novel quantum devices—from tunneling diodes and transistors, to spin-FETs, valley-FETs, and qubits. The physics are highlighted and the opportunities and challenges of exploiting the unique quantum properties of 2D materials to enable revolutionary ultra-energy-efficient quantum devices are analyzed.

Abstract

As an approximation to the quantum state of solids, the band theory, developed nearly seven decades ago, fostered the advance of modern integrated solid-state electronics, one of the most successful technologies in the history of human civilization. Nonetheless, their rapidly growing energy consumption and accompanied environmental issues call for more energy-efficient electronics and optoelectronics, which necessitate the exploration of more advanced quantum mechanical effects, such as band-to-band tunneling, spin–orbit coupling, spin–valley locking, and quantum entanglement. The emerging 2D layered materials, featured by their exotic electrical, magnetic, optical, and structural properties, provide a revolutionary low-dimensional and manufacture-friendly platform (and many more opportunities) to implement these quantum-engineered devices, compared to the traditional electronic materials system. Here, the progress in quantum-engineered devices is reviewed and the opportunities/challenges of exploiting 2D materials are analyzed to highlight their unique quantum properties that enable novel energy-efficient devices, and useful insights to quantum device engineers and 2D-material scientists are provided.

Nature Electronics, Published online: 25 April 2022; doi:10.1038/s41928-022-00754-6

Few-nanometre-thick flakes of trigonal and monoclinic Cr5Te8 can be grown using chemical vapour deposition, with the monoclinic phase exhibiting an anomalous Hall conductivity of 650 Ω–1 cm–1 and anomalous Hall angle of 5%.

Nature Communications, Published online: 25 April 2022; doi:10.1038/s41467-022-29825-0

While internal electric fields alter charge-separation dynamics in solar-to-chemical conversions, a greater understanding of such processes is necessary. Here, authors analyze charge transfer dynamics modulated by built-in electric fields and identify carrier drift distances as a critical parameter.

Nature Physics, Published online: 25 April 2022; doi:10.1038/s41567-022-01589-w

In graphene, the spin and valley degrees of freedom combine into a higher-order isospin. Now, a full map of the phase diagram of this isospin is measured in the moiré bands of twisted bilayer graphene.

Nature Nanotechnology, Published online: 25 April 2022; doi:10.1038/s41565-022-01118-z

Anion-selective covalent organic framework (COF) membranes fabricated using laminar assembly and interfacial polymerization exhibit enhanced potential for osmotic power generation.

Nature Electronics, Published online: 21 April 2022; doi:10.1038/s41928-022-00746-6

High-quality van der Waals contacts between metals and two-dimensional semiconductors can be created using a selenium buffer layer that is deposited before the metal deposition process.

Through exfoliation of the electrochemically lithium-intercalated MoS₂ in iodoacetamide water solution, the covalent functionalization of single-layer MoS₂ with iodoacetamide molecules can be shortened to 15 min, and functionalized MoS₂ membranes are fabricated via vacuum filtration. Under reverse osmosis mode, the functionalized MoS₂ membranes exhibit rejection rates of >90% and >80% for various dyes and NaCl, respectively.

Abstract

Transition metal dichalcogenide membranes exhibit good antiswelling properties but poor water desalination property. Here, a one-step covalent functionalization of MoS₂ nanosheets for membrane fabrication is reported, which is accomplished by simultaneous exfoliating and grafting the lithium-ion-intercalated MoS₂ in organic iodide water solution. The lithium intercalation amount in MoS₂ is optimized so that the quality of the produced 2D nanosheets is improved with homogeneous size distribution. The lamellar MoS₂ membranes are tested in reverse osmosis (RO), and the functionalized MoS₂ membrane exhibits rejection rates of >90% and >80% for various dyes (Rhodamine B, Crystal Violet, Acid Fuchsin, Methyl Orange, and Evans Blue) and NaCl, respectively. The excellent ion-sieving performance and good water permeability of the functionalized MoS₂ membranes are attributed to the suitable channel widths that are tuned by iodoacetamide. Furthermore, the stability of the functionalized MoS₂ membranes in NaCl and dye solutions is also confirmed by RO tests. Molecular dynamics simulation shows that water molecules tend to form a single layer between the amide-functionalized MoS₂ layers but a double layer between the ethanol-functionalized MoS₂ (MoS₂-ethanol) layers, which indicates that a less packed structure of water between the MoS₂-ethanol layers leads to lower hydrodynamic resistance and higher permeation.