Jiuxiang Dai

Nature Communications, Published online: 04 October 2024; doi:10.1038/s41467-024-52944-9

A novel technique utilizes in situ generated Na–W–S–O droplets to etch 1D nanotrenches in few-layer WS₂. The study further demonstrates the modulation of inkjet-printed Na₂WO₄-Na₂SO₄ particles for switching between etching and growth modes. This versatile approach facilitates the creation of 1D nanochannels on 2D TMDCs, enhancing their optical and optoelectronic applications.

Abstract

Layer number-dependent band structures and symmetry are vital for the electrical and optical characteristics of 2D transition metal dichalcogenides (TMDCs). Harvesting 2D TMDCs with tunable thickness and properties can be achieved through top-down etching and bottom-up growth strategies. In this study, a pioneering technique that utilizes the migration of in situ generated Na-W-S-O droplets to etch out 1D nanotrenches in few-layer WS₂ is reported. 1D WS₂ nanotrenches are successfully fabricated on the optically inert bilayer WS_2, showing pronounced photoluminescence and second harmonic generation signals. Additionally, the modulation of inkjet-printed Na₂WO₄-Na₂SO₄ particles to switch between the etching and growth modes by manipulating the sulfur supply is demonstrated. This versatile approach enables the creation of 1D nanochannels on 2D TMDCs. The research presents exciting prospects for the top-down and bottom-up fabrication of 1D-2D mixed-dimensional TMDC nanostructures, expanding their use for electronic and optoelectronic applications.

VB−$V_{\rm {B}}^{-}$ color center in hBN film is explored as 2D quantum sensor to detect the near-surface magnon stray field. With nanometers probe-sample distance and the uniform out-of-plane axis of spin sensor, the excitation and propagation of magnons in magnetic insulators are revealed with high accuracy and diffraction-limited spatial resolution.

Abstract

Magnonic devices are extensively studied for energy-efficient information processing. High spatial resolution and high accuracy measurement is required to characterize the excitation and distribution of magnons. Here, sensing and imaging of magnons in the magnetic insulator Y3Fe5O12$\rm Y_3 Fe_5 O_{12}$ (YIG) is realized with negatively charged boron vacancy (VB−$V_{\rm {B}}^-$) spin defects in 2D hexagonal boron nitride (hBN). Thermal magnon noise is studied through spin relaxometry, illustrating the nanometers proximity of the 2D quantum sensor over a large area. The small probe-sample standoff distance helps to detect weak signals with diffraction-limited spatial resolution. The uniform out-of-plane symmetry axis of VB−$V_{\rm {B}}^{-}$ is further utilized to study perpendicular magnetic anisotropy (PMA). It effectively extracts the stray field of microwave-excited magnons from the direct stripline field. The distributions of propagating and localized magnons in different structures are subsequently imaged and analyzed. The work provides the strategy for utilizing the distinctive advantages of the van der Waals quantum sensor in magnetic imaging. The results will promote the development of magnonic devices for diverse applications.

Advanced in situ biasing and atomic-scale imaging in an aberration-corrected scanning transmission electron microscope are employed to investigate and manipulate in real space local picometer-level structure variations and polarization in a prototype 2D vdW ferroelectrics InSe. Intralayer sliding within each Se–In–In–Se quadruple-layer is identified to be responsible for switchable out-of-plane polarization and ferroelectricity of InSe.

Abstract

Ferroelectric 2D van der Waals (vdW) layered materials are attracting increasing attention due to their potential applications in next-generation nanoelectronics and in-memory computing with polarization-dependent functionalities. Despite the critical role of polarization in governing ferroelectricity behaviors, its origin and relation with local structures in 2D vdW layered materials have not been fully elucidated so far. Here, intralayer sliding of approximately six degrees within each quadruple-layer of the prototype 2D vdW ferroelectrics InSe is directly observed and manipulated using sub-angstrom resolution imaging and in situ biasing in an aberration-corrected scanning transmission electron microscope. The in situ electric manipulation further indicates that the reversal of intralayer sliding can be achieved by altering the electric field direction. Density functional theory calculations reveal that the reversible picometer-level intralayer sliding is responsible for switchable out-of-plane polarization. The observation and manipulation of intralayer sliding demonstrate the structural origin of ferroelectricity in InSe and establish a dynamic structural variation model for future investigations on more 2D ferroelectric materials.

Nature Electronics, Published online: 09 October 2024; doi:10.1038/s41928-024-01260-7

Nature Electronics, Published online: 09 October 2024; doi:10.1038/s41928-024-01251-8

This comprehensive review focuses on engineering novel 2D material-based electrocatalysts and their application to seawater splitting. The review briefly introduces the mechanism of seawater splitting and the primary challenges of 2D materials. Highlight the unique advantages and regulating strategies for seawater electrolysis based on recent advancements. Provides valuable insights for the rational design and development of cutting-edge 2D material electrocatalysts for seawater-electrolysis applications.

Abstract

Applying catalysts for electrochemical energy conversion holds great promise for developing clean and sustainable energy sources. One of the main advantages of electrocatalysis is its ability to reduce conversion energy loss significantly. However, the wide application of electrocatalysts in these conversion processes has been hindered by poor catalytic performance and limited resources of catalyst materials. To overcome these challenges, researchers have turned to two-dimensional (2D) materials, which possess large specific surface areas and can easily be engineered to have desirable electronic structures, making them promising candidates for high-performance electrocatalysis in various reactions. This comprehensive review focuses on engineering novel 2D material-based electrocatalysts and their application to seawater splitting. The review briefly introduces the mechanism of seawater splitting and the primary challenges of 2D materials. Then, we highlight the unique advantages and regulating strategies for seawater electrolysis based on recent advancements. We also review various 2D catalyst families for direct seawater splitting and delve into the physicochemical properties of these catalysts to provide valuable insights. Finally, we outline the vital future challenges and discuss the perspectives on seawater electrolysis. This review provides valuable insights for the rational design and development of cutting-edge 2D material electrocatalysts for seawater-electrolysis applications.

The study uses the low-symmetry Weyl semimetal TaIrTe₄ and above-room-temperature van der Waals ferromagnet Fe₃GaTe₂ to achieve the field-free magnetization switching. The unconventional SOT effective field efficiency is determined to be 0.37, and the switching-polarity-change magnetic field is as high as 252 mT, indicating a robust field-free switching against the external magnetic field.

Abstract

The emerging all-van der Waals (vdW) magnetic heterostructure provides a new platform to control the magnetization by the electric field beyond the traditional spintronics devices. One promising strategy is using unconventional spin-orbit torque (SOT) exerted by the out-of-plane polarized spin current to enable deterministic magnetization switching and enhance the switching efficiency. However, in all-vdW heterostructures, large unconventional SOT remains elusive and the robustness of the field-free switching against external magnetic field has not been examined, which hinders further applications. Here, the study demonstrates the field-free switching in an all-vdW heterostructure combining a type-II Weyl semimetal TaIrTe₄ and above-room-temperature ferromagnet Fe₃GaTe₂. The fully field-free switching can be achieved at 2.56 × 10¹⁰ A m⁻² at 300 K and a large SOT effective field efficiency of the out-of-plane polarized spin current generated by TaIrTe₄ is determined to be 0.37. Moreover, it is found that the switching polarity cannot be changed until the external in-plane magnetic field reaches 252 mT, indicating a robust switching against the magnetic field. The numerical simulation suggests the large unconventional SOT reduces the switching current density and enhances the robustness of the switching. The work shows that all-vdW heterostructures are promising candidates for future highly efficient and stable SOT-based devices.

The electronic delocalization of blue-arsenic-phosphorus (β-AsP) in the vicinity of implementation sites is achieved through the engineering of trace vacancies and doping, significantly optimizing physicochemical properties. Consequently, extremely optically-, electrically-, and thermally-driven high-performance multisource logic devices are developed and comprehensively investigated through precisely tuning electron delocalization.

Abstract

Delocalized electron and phonon structures are directives for rationally tuning the intrinsic physicochemical properties of 2D materials by redistributing electronic density. However, it is still challenging to accurately manipulate the delocalized electron and systematically study the relationships between physiochemical properties and practical nanodevices. Herein, the effects of delocalized electrons engineering on blue-arsenic-phosphorus (β-AsP)-based practical devices are systematically investigated via implementing vacancies or heteroatom doping. A tendency of carrier conductivity property from “half-metal” to “metal” is initially found when tuning the electronic structure of β-AsP with adjustable vacancy concentrations below 2 at% or above 3 at%, which can be ascribed to the introduction of delocalized electrons that cause asymmetric contributions to the electronic states near the implementation site. In optical logic device simulations, broadband response, triangular wave circuit system signal, and reverse polarization anisotropy are achieved by adjusting the vacancy concentration, while extinction ratios are as high as 1561. The electric and thermic-logic devices realize the highest available reported giant magnetoresistance (MR) up to 10¹³% and 10³⁹% at vacancy concentrations of 1.67% and 0.89%, respectively, which is significantly superior to the reports. The results shed light on the electronic delocalization strategy of regulating internal structures to achieve highly efficient nanodevices.

Nature Materials, Published online: 07 October 2024; doi:10.1038/s41563-024-02020-w

A giant valley Zeeman effect in vanadium-doped WSe₂ monolayers through circularly polarized magneto-photoluminescence experiments at low temperature is reported. Ab initio calculations corroborate the experimental observations by confirming a magnetic ordering for the vanadium states. The results shed light on the promising magneto-optical properties of vanadium-doped WSe₂ monolayers for spintronic and valleytronic functionalities.

Abstract

2D dilute magnetic semiconductors (DMS) based on transition metal dichalcogenides (TMD) offer an innovative pathway for advancing spintronic technologies, including the potential to exploit phenomena such as the valley Zeeman effect. However, the impact of magnetic ordering on the valley degeneracy breaking and on the enhancement of the optical transitions g-factors of these materials remains an open question. Here, a giant effective g-factors ranging between ≈−27 and −69 for the bound exciton at 4 K in vanadium-doped WSe₂ monolayers, obtained through magneto-photoluminescence (PL) experiments is reported. This giant g-factor disappears at room temperature, suggesting that this response is associated with a magnetic ordering of the vanadium impurity states at low temperatures. Ab initio calculations for the vanadium-doped WSe₂ monolayer confirm the existence of magnetic ordering of the vanadium states, which leads to degeneracy breaking of the valence bands at K and K′. A phenomenological analysis is employed to correlate this splitting with the measured enhanced effective g-factor. The findings shed light on the potential of defect engineering of 2D materials for spintronic applications.

A distinct rhombohedral R3 ferroelectric phase is successfully synthesized in Mn-doped Hf_0.5Zr_0.5O₂ epitaxial thin films, with exceptional remnant polarization, retention, and endurance. This advancement enables the controlled phase transition among R3m, R3, and Pca2₁ polar phases by simply adjusting the Mn dopant concentration and film thickness. The research broadens the understanding of HfO₂-based ferroelectric materials and potentially promotes the advancement of integrated ferroelectric devices.

Abstract

HfO₂-based ferroelectric materials are emerging as key components for next-generation nanoscale devices, owing to their exceptional nanoscale properties and compatibility with established silicon-based electronics infrastructure. Despite the considerable attention garnered by the ferroelectric orthorhombic phase, the polar rhombohedral phase has remained relatively unexplored due to the inherent challenges in its stabilization. In this study, the successful synthesis of a distinct ferroelectric rhombohedral phase is reported, i.e., the R3 phase, in Mn-doped Hf_0.5Zr_0.5O₂ (HZM) epitaxial thin films, which stands different from the conventional Pca2₁ and R3m polar phases. These findings reveal that this R3 phase HZM film exhibits a remnant polarization of up to 47 µC cm^{− 2} at room temperature, along with an exceptional retention capability projected to exceed a decade and an endurance surpassing 10⁹ cycles. Moreover, it is demonstrated that by modulating the concentration of Mn dopant and the film's thickness, it is possible to selectively control the phase transition between the R3, R3m, and Pca2₁ polar phases. This research not only sheds new light on the ferroelectricity of the HfO₂ system but also paves the way for innovative strategies to manipulate ferroelectric properties for enhanced device performance.