Two-dimensional (2D) magnetic materials and their van der Waals (vdW) heterostructures offer a unique platform for investigating low-dimensional magnetic interactions and developing next-generation spintronic devices. This study employs electronic tunneling spectroscopy to systematically explore the interfacial magnetic coupling mechanisms in CrI3/CrBr3 vdW heterostructures. Experimentally, we observe complex tunneling magnetoresistance (TMR) behaviors, including multi-step jumps and asymmetric hysteresis, with their magnetic origins confirmed through temperature-dependent measurements. Theoretically, we develop a one-dimensional (1D) spin-chain model that successfully reproduces the TMR characteristics, unveiling the synergistic role of interfacial Dzyaloshinskii-Moriya interaction (DMI, ∼10.8 μeV) and ferromagnetic exchange (∼13.5 μeV) in governing magnetic configurations. We find that interfacial DMI, driven by broken inversion symmetry, induces spin canting in the ferromagnetic layers, profoundly influencing TMR behavior. This work not only provides a novel physical framework for understanding interfacial coupling in vdW magnetic heterostructures but also charts a pathway for designing multi-state memory devices through interfacial engineering.

Two-dimensional (2D) magnetic materials and their van der Waals (vdW) heterostructures offer a unique platform for investigating low-dimensional magnetic interactions and developing next-generation spintronic devices. This study employs electronic tunneling spectroscopy to systematically explore the interfacial magnetic coupling mechanisms in CrI3/CrBr3 vdW heterostructures. Experimentally, we observe complex tunneling magnetoresistance (TMR) behaviors, including multi-step jumps and asymmetric hysteresis, with their magnetic origins confirmed through temperature-dependent measurements. Theoretically, we develop a one-dimensional (1D) spin-chain model that successfully reproduces the TMR characteristics, unveiling the synergistic role of interfacial Dzyaloshinskii-Moriya interaction (DMI, '10.8 mu eV) and ferromagnetic exchange ('13.5 mu eV) in governing magnetic configurations. We find that interfacial DMI, driven by broken inversion symmetry, induces spin canting in the ferromagnetic layers, profoundly influencing TMR behavior. This work not only provides a novel physical framework for understanding interfacial coupling in vdW magnetic heterostructures but also charts a pathway for designing multi-state memory devices through interfacial engineering.

Interlayer stacking is an important degree of freedom to tune the properties of two-dimensional materials and offers enormous opportunities for designing functional devices. As a classic example, rhombohedral-stacked (3R) two-dimensional materials exhibit ferroelectricity and optical nonlinearity that are non-existent in naturally abundant hexagonal-stacked (2H) counterparts. However, the ability to grow stacking-controlled large-area films remains challenging due to the thermodynamic competition of different polytypes. Here we report the chemical vapour deposition growth of two-inch wafer-scale 3R-MoS2 films with high phase purity by homoepitaxy on top of a crystalline monolayer MoS2. A defect-promoted nucleation mechanism was proposed, in which Mo-substituted sulfur vacancy is identified as one of the possible defects promoting 3R stacking. We fabricate ferroelectric semiconductor field-effect transistors with 3R-MoS2 channels and demonstrate non-volatile memory characteristics. The control of interlayer stacking is an essential step towards the large-scale production of two-dimensional materials for multifunctional integration.

Tunneling techniques are pivotal for probing 2D magnetic materials. While the Fowler-Nordheim model describes tunneling in bulk materials through bias-induced triangular potentials, van der Waals layered systems require special consideration of interlayer gaps. The fundamental mechanisms of tunneling processes in van der Waals magnetic materials are delved into, with a specific emphasis on CrBr3. Layer-resolved quasi-resonant tunneling (QRT) mediated by ladder-shaped barriers is revealed. QRT occurs because the outermost CrBr3 conduction band aligns with the Fermi level of the tunneling electrode under the bias voltage tilting, resulting in an increased tunneling probability and enhanced current. Two competing mechanisms driven by the magnetic field-the suppression of spin fluctuations leading to negative tunneling magnetoresistance (TMR) and the spin-flip-induced elevation of the conduction band energy causing positive TMR-are identified to explain the diverse behaviors of tunneling magnetoresistance under different bias voltages and temperatures. The work establishes van der Waals heterostructures as distinct tunneling systems differing fundamentally from conventional bulk barriers, while introducing the QRT concept as a critical advancement in understanding electronic tunneling in layered materials.

The rapidly evolving communication field demands higher data capacity, faster transmission speeds, and improved anti-interference capabilities. However, the physical limitations of silicon-based photonics technology hinder the realization of photodetectors and other active devices. The discovery of two-dimensional (2D) materials, such as graphene, has opened promising opportunities for on-chip photodetection, showcasing distinctive physical and chemical properties and ultrathin nature. In this review, we first describe several representative 2D materials, including graphene, black phosphorus, and transition metal dichalcogenides (TMDCs). These materials offer diverse band structures and properties, presenting a plethora of options for varied applications. Then we highlight the utilization of these 2D materials in the development of highperformance photodetection devices, including photodiodes, field-effect transistors, and photodetectors. Furthermore, we delve into the practical applications of photodetectors, including room-temperature imaging, visual sensors, spectrometers, ranging, and other optoelectronic integrated systems. These real-world applications vividly demonstrate the versatility and potential of 2D materials across diverse fields. Overall, the unique structures and properties of 2D materials offer new possibilities for applications across various domains. Future research should be devoted to further explore the properties and applications of 2D materials to advance their development in the field of science and technology. (c) 2024 Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Electrons and holes, fundamental charge carriers in semiconductors, dominate optical transitions and detection processes. Twisted van der Waals (vdW) heterostructures offer an effective approach to manipulate radiation, separation, and collection processes of electron-hole pairs by creating an atomically sharp interface. Here, we demonstrate that twisted interfaces in vdW layered black phosphorus (BP), an infrared semiconductor with highly anisotropic crystalline structure and properties, can significantly alter both recombination and separation processes of electron-hole pairs. On the one hand, the twisted interface breaks the symmetry of optical transition states resulting in infrared light emission of originally symmetry-forbidden optical states along the zigzag direction. On the other hand, spontaneous electronic polarization/bulk photovoltaic effect is generated at the twisted interface enabling effective separation of electron-hole pairs without external voltage bias. This is supported by first-principles calculations and repeated experiments at various twisted angles from 0 to 90°. Importantly, these phenomena can be observed in twisted heterostructures with thickness beyond two-dimensional. Our results suggest that the engineering of vdW twisted interfaces is an effective strategy for manipulating the optoelectronic properties of materials and constructing functional devices.

Structural engineering is crucial for tuning the properties of artificial materials. As one of the most important two-dimensional (2D) materials, black phosphorus (BP) has been rediscovered in 2014 and attracted tremendous attentions all over the world. It shows great potentials in optoelectronic and integrated photonic applications due to the direct and tunable bandgap, high carrier mobility, and intrinsic anisotropy. However, some deficiencies are yet to be settled before its large-scale applications, such as the massive synthesis methods and structure-property relationship. To investigate the influence of structural engineering on the performance of 2D BP-based devices thoroughly, recent studies on deformation, atomic defects, superlattice, alloying, thickness and phase transition are maximality summarized in this review covering from the intrinsic properties to optoelectronic applications. Benefiting from the broad research in this field, challenges and opportunities of 2D BP for advanced integrated photonic applications are also provided, which supplies a useful reference to realize large-scale 2D BP-based all-optical communications in future.

The increasing demand for computation requires the development of energy-efficient logic devices with reduced dimensions. Owing to their atomic thickness, 2D semiconductors are expected to provide possible solutions at the sub-1 nm technology node. Furthermore, taking advantage of the van der Waals nature, the low-temperature back-end of line integration with silicon may occur in the near future. In this perspective, vital progress in material synthesis, device engineering, and integration technologies toward integrated circuits based on 2D materials is reviewed. The challenges and important milestones on the roadmap for the next decade toward the fab adoption of 2D materials are outlined. Particularly, performance, power, area, cost, and equipment for further technology development in this area are proposed as key metrics and enablers.

We report an observation of quantum oscillations (QOs) in the correlated insulators with valley anisotropy of twisted double bilayer graphene (TDBG). The anomalous QOs are best captured in the magneto resistivity oscillations of the insulators at v = -2, with a period of 1/B and an oscillation amplitude as high as 150 kΩ. The QOs can survive up to 10 K, and above 12 K, the insulating behaviors are dominant. The QOs of the insulator are strongly D dependent: the carrier density extracted from the 1/B periodicity decreases almost linearly with D from -0.7 to -1.1 V/nm, suggesting a reduced Fermi surface; the effective mass from Lifshitz-Kosevich analysis depends nonlinearly on D, reaching a minimal value of 0.1 me at D = -1.0 V/nm. Similar observations of QOs are also found at v = 2, as well as in other devices without graphite gate. We interpret the D sensitive QOs of the correlated insulators in the picture of band inversion. By reconstructing an inverted band model with the measured effective mass and Fermi surface, the density of state at the gap, calculated from thermal broadened Landau levels, agrees qualitatively with the observed QOs in the insulators. While more theoretical understandings are needed in the future to fully account for the anomalous QOs in this moiré system, our study suggests that TDBG is an excellent platform to discover exotic phases where correlation and topology are at play.

信息社会的飞速发展对信息存储、加工、传输能力提出了与日俱增的迫切需求。随着“摩尔定律”逐渐逼近极限，半导体工业急需寻求新的解决方案。二维材料因为原子级厚度的尺寸特点，表面无悬挂键的结构优势加上极大比表面积导致的对电、光等调控手段的敏感性被认为是“后摩尔定律”时代半导体工业新的突破口。松山湖材料实验室引进一批国内外顶级科学家，组建二维材料团队，以基础科研为根基，以工程应用为导向，重点攻关其中关键问题。其目标在于取得有世界级重大影响力的科研成果，布局我国二维材料产业。

2D semiconducting transition metal dichalcogenides (TMDs) are considered promising building blocks for emergent electronic and optoelectronic devices. As one of the representatives of 2D semiconductors, monolayer MoSe2 has excellent electrical and optical properties and has attracted a lot of research interest recently. To realize various device applications, large‐scale synthesis of monolayer MoSe2 with high crystal quality is critical, yet remains challenging. Herein, the growth of monolayer MoSe2 at a 4 inch wafer‐scale by chemical vapor deposition is demonstrated. Based on a multisource design and vertical placement of substrates, wafer‐scale continuity and uniformity of layer thickness, e.g., the monolayer, are achieved. This growth technique is also applicable to the wafer‐scale growth of other 2D semiconductors such as WS2 and MoS2.

As an emerging research field, two-dimensional (2D) metals have been the subject of increasing research efforts in recent years due to their potential applications. However, unlike typical 2D layered materials, such as graphene, which can be exfoliated from their bulk parent compounds, it is hardly possible to produce 2D metals through exfoliation techniques due to the absence of Van der Waals gaps. Indeed, the lack of effective material preparation methods severely limits the development of this research field. Here, we report a PDMS-assisted hot-pressing method in glovebox to obtain ultraflat nanometer-thick 2D metals/metal oxide amorphous films of various low-melting-point metals and alloys, e.g., gallium (Ga), indium (In), tin (Sn), and Ga0.87Ag0.13 alloy. The valence states extracted from X-ray photoelectron spectroscopy (XPS) indicate that the ratios of oxidation to metal in our 2D films vary among metals. The temperature-dependent electronic measurements show that the transport behavior of 2D metal/metal oxide films conform with the 2D Mott’s variable range hopping (VRH) model. Our experiments provide a feasible and effective approach to obtain various 2D metals.

Atomically thin van der Waals magnetic materials have gained intensive research interests in the past few years. The topic paves a way to understand the stabilization and dissipation mechanisms of longrange magnetic order in the 2D limit, which is crucial for both fundamental condensed matter physics research and technological applications. However, limited by the sample size, conventional experimental techniques such as neutron diffraction spectrum and magnetization measurements are difficult to be applied to these atomically thin materials. At the same time, electronic tunneling transport measurements have been proved to be a powerful technique in the study of 2D magnetism. Here we review the electronic tunneling transports in magnetic 2D crystals, especially the detection of the phase boundaries of 2D magnets, focusing on two-material systems, i.e. chromium halides and manganese phosphorus trisulfides. In addition, the magnetic van der Waals Josephson junctions and the spin valve devices based on the 2D magnetic metals are applied to probe 2D magnetism as well. Finally, we discuss the current challenges and perspectives of potential applications of 2D van der Waals magnetic materials. (C) 2021 The Author(s). Published by Elsevier Ltd.

With the rapid demand growth of green energy technologies, solar cell has been considered as a very promising technology to address current energy and environmental issues. Among them, perovskite solar cells (PSCs) have attracted much research interest in recent years due to the prominent advantages of light weight, good flexibility, low cost, and comparable power conversion efficiency (PCE) to that of traditional commercial solar cells (ie, amorphous silicon, GaAs, and CdTe). Meanwhile, elemental two-dimensional (2D) graphene and its derivatives, which possess the outstanding advantages of abundant functional groups, good environmental stability, and good compactness, have been extensively studied on the integration with PSC devices. The review introduces the properties and preparation methods of graphene and its derivatives, and the applications in PSC are summarized in detail. Ultimately, the critical challenges and prospects for the further development of graphene and its derivatives in PSCs are discussed.

For a long time, it has been generally acknowledged that low-dimensional (lower than three-dimensions) long-range orders cannot stay stable at any finite temperature, because temperature-induced fluctuations can destroy any long-range orders in low-dimensional systems supported by isotropic short-range interactions. However, this theorem requires that the interaction must be short-range and isotropic. In fact, many low-dimensional systems do not meet these two requirements. For example, due to the strong anisotropy in two-dimensional CrI3 crystals, there is a band gap in the magnon spectrum. When the excitation energy from temperature is much lower than the band gap, the magneton cannot be excited by temperature on a large scale, and the long-range magnetic order in the two-dimensional system will not be destroyed. Various methods have been used to characterize the magnetic order in atomically thin CrI3 crystals, and a lot of attempts have been made to manipulate the magnetic structure in the system. Focusing on CrI3, in this article we review the recent studies on growth, magnetic structure measurement and manipulation of two-dimensional magnetic materials, and also discuss the prospects for the next phase of research from the perspectives of basic condensed matter physics research and electronic engineering applications.

Atomically dispersed catalysts (ADCs) have emerged as a rising star of new materials, exhibiting remarkable catalytic efficiency, selectivity and recyclability. However, little is known about the atomic-scale mechanisms leading to the generic synthesis of fully exposed metals, the feasibility of tailoring metal's coordination environments and the thermal robustness. Here we demonstrate the strong metal support interactions (SMSI) as one of the key factors to universally construct a series of atomically dispersed single metals and synergetic bimetals for high-performance catalysts. The SMSI is realized through the anchoring effects of hybrid sp(2)- and sp(3)-carbons on the surface of nanodiamond@graphene (ND@G) support. Such SMSI assures the effective tuning of metal's coordination numbers by means of either controlling mass loading or introducing complementary species. Furthermore, the impressive thermal stability of ND@G-supported Pt-Sn catalyst as well as the failure route are revealed by atomic resolution in-situ observations. This work not only paves the way towards a library of highly tunable and stable ADCs, but also sheds light on the fundamental regulating principles for their industrial applications. (C) 2021 The Authors. Published by Elsevier Ltd.

Subjected to an adequately high magnetic field, Landau levels (LLs) form to alter the electronic transport behavior of a semiconductor. Especially in two-dimensional (2D) limit, quantum Hall effect sheds light on a variety of intrinsic properties of 2D electronic systems. With the raising quality of field effect transistors (FET) based on few-layer black phosphorus (BP), electronic transport in quantum limit (quantum transport) has been extensively studied in literatures. This chapter investigates the electronic transport in few-layer BP, especially in quantum limit. At the beginning of this chapter, a brief introduction to the background of LL, edge state, and quantum Hall effect will be delivered. We then examine the fabrication of high-quality FET based on BP and their electronic performances followed by exploring the magnetoresistances of these high-quality devices which reveal Shubnikov-de Haas (SdH) oscillations and quantum Hall effect in BP. Intrinsic parameters like effective mass, Landé g-factor, and so on are discussed based on quantum transport.

The magnetic state of atomically thin semiconducting layered antiferromagnets such as CrI3 and CrCl3 can be probed by forming tunnel barriers and measuring their resistance as a function of magnetic field (H) and temperature (T). This is possible because the spins within each individual layer are ferromagnetically aligned and the tunneling magnetoresistance depends on the relative orientation of the magnetization in adjacent layers. The situation is different for systems that are antiferromagnetic within the layers in which case it is unclear whether magnetoresistance measurements can provide information about the magnetic state. Here, we address this issue by investigating tunnel transport through atomically thin crystals of MnPS3, a van der Waals semiconductor that in the bulk exhibits easy-axis antiferromagnetic order within the layers. For thick multilayers below T ∼ 78 K, a T-dependent magnetoresistance sets in at μ0H ∼ 5 T and is found to track the boundary between the antiferromagnetic and the spin-flop phases known from bulk measurements. We show that the magnetoresistance persists as thickness is reduced with nearly unchanged characteristic temperature and magnetic field scales, albeit with a different dependence on H, indicating the persistence of magnetism in the ultimate limit of individual monolayers.

The magnetic state of atomically thin semiconducting layered antiferromagnets such as CrI_3 and CrCl_3 can be probed by forming tunnel barriers and measuring their resistance as a function of magnetic field (H) and temperature (T). This is possible because the tunneling magnetoresistance originates from a spin-filtering effect sensitive to the relative orientation of the magnetization in different layers, i.e., to the magnetic state of the multilayers. For systems in which antiferromagnetism occurs within an individual layer, however, no spin-filtering occurs: it is unclear whether this strategy can work. To address this issue, we investigate tunnel transport through atomically thin crystals of MnPS_3, a van der Waals semiconductor that in the bulk exhibits easy-axis antiferromagnetic order within the layers. For thick multilayers below T≃ 78 K, a T-dependent magnetoresistance sets-in at ∼ 5 T, and is found to track the boundary between the antiferromagnetic and the spin-flop phases known from bulk magnetization measurements. The magnetoresistance persists down to individual MnPS_3 monolayers with nearly unchanged characteristic temperature and magnetic field scales, albeit with a different dependence on H. We discuss the implications of these finding for the magnetic state of atomically thin MnPS_3 crystals, conclude that antiferromagnetic correlations persist down to the level of individual monolayers, and that tunneling magnetoresistance does allow magnetism in 2D insulating materials to be detected even in the absence of spin-filtering.

Electrons hopping in two-dimensional honeycomb lattices possess a valley degree of freedom in addition to charge and spin. In the absence of inversion symmetry, these systems were predicted to exhibit opposite Hall effects for electrons from different valleys. Such valley Hall effects have been achieved only by extrinsic means, such as substrate coupling, dual gating, and light illuminating. Here we report the first observation of intrinsic valley Hall transport without any extrinsic symmetry breaking in the non-centrosymmetric monolayer and trilayer MoS2, evidenced by considerable nonlocal resistance that scales cubically with local resistance. Such a hallmark survives even at room temperature with a valley diffusion length at micron scale. By contrast, no valley Hall signal is observed in the centrosymmetric bilayer MoS2. Our work elucidates the topological origin of valley Hall effects and marks a significant step towards the purely electrical control of valley degree of freedom in topological valleytronics.