Jiuxiang Dai

In this work, the V-doped MoS₂ by a two-step synthesis method is successfully obtained. Differential pulse voltammetry test results show that V-SACs are able to achieve the serotonin lowest detection limit down to 1 pM. There are two linear regions (1 pM ∼100 pM and 100 pM ∼100 µM), and the sensing sites are V-SACs and S-bonding on the surface, respectively.

Abstract

The detection of monoamine neurotransmitters is of paramount importance as the neurotransmitters are the chemical messengers regulating the gut-brain axis (GBA). It requires real-time, ultrasensitive, and selective sensing of the neurotransmitters in the gastric/intestinal fluid. However, multi-components present in the gastric/intestinal fluid make sensing challenging to achieve in terms of ultra-high sensitivity and selectivity. Herein, an approach is introduced to utilize vanadium single atom catalytic (SAC) centers in van der Waals MoS₂ (V-MoS₂) to selectively detect real-time serotonin (5-HT) in artificial gastric/intestinal fluid. The synergetic effect of V-SACs and the surface S-bonds on the MoS₂ surface, enables an extremely wide range of 5-HT detection (from 1 pM to 100 µM), with optimum selectivity and interference resistance. By combining density functional theory calculations and scanning transmission electron microscopy, it is concluded that the V-SACs embedded in the MoS₂ network create active sites that greatly facilitate the charge exchange between the material and the 5-HT molecules. This result allows the 5-HT detection in GBA studies to be more reliable, and the material tunability provides a general platform to achieve real-time and multi-component detection of other monoamine neurotransmitters in GBA such as dopamine and norepinephrine.

Author(s): Ming Xie, Mohammad Hafezi, and Sankar Das Sarma

Moiré superlattices based on two-dimensional transition metal dichalcogenides (TMDs) have emerged as a highly versatile and fruitful platform for exploring correlated topological electronic phases. One of the most remarkable examples is the recently discovered fractional quantum anomalous Hall effec…

[Phys. Rev. Lett. 133, 136403] Published Thu Sep 26, 2024

Highlights

• “Zero-strain” NiNb₂O₆ fibers with nanosized primary particles are explored as an all-climate anode material with comprehensively good Li⁺-storage properties.

• The almost completely opposite volume changes of electrochemical inactive NiO₆ octahedra and active NbO₆ octahedra are achieved through reversible O movement, leading to the “zero-strain” behavior of NiNb₂O₆ with minor unit-cell-volume change and excellent cyclability in a broad temperature range.

• The gained insight can provide guide for the exploration of high-performance energy-storage materials working at harsh temperatures.

Nature, Published online: 25 September 2024; doi:10.1038/s41586-024-07958-0

A van der Waals heterostructure (vdWH) contact strategy for 2D field-effect transistors (FETs) is proposed by introducing a vdW semiconductor intercalation between the metal electrode and the 2D channel. This strategy enabled the complementary doping within vdWHs, Ohmic contacts at electrical interfaces, and symmetric currents in p-type and n-type 2D-FETs.

Abstract

Incorporating atomically thin 2D semiconductors (2DSCs) into the vertical complementary field-effect transistors (CFETs) is of great significance in enabling devices to break through the sub-nanometer scaling limit. However, due to the lack of effective doping technology and the difficult-to-control electrode interface, simultaneously realizing high-performance p-type and n-type devices using a single metal electrode presents great challenges for 2D-CFETs design. In this study, an innovative electrical contact strategy is proposed by constructing van der Waals heterojunction (vdWH) using 2DSCs to regulate the electrical contact properties between the metal electrode and 2DSC channel. First-principles calculations reveal that degenerate or quasi-degenerate complementary doping is achieved in a series of transition metal dichalcogenides (TMDs) by designing (quasi-)broken-gap vdWHs and utilizing their interlayer charge transfer. Metal-2DSC contact barriers can be effectively regulated by introducing 2DSC intercalation and constructing vdWH. P-type (quasi-)Ohmic contacts are realized between Au electrode and various TMD channels, as well as between WTe₂ channel and different metal electrodes. Moreover, quantum transport simulations present the remarkable on-current over 10² µA µm⁻¹ in both p-type and n-type 2D-FETs by employing the vdWH and metal-vdWH electrodes. The proposed vdWH strategy is applicable to various metal-2DSC contacts and will shed light on future high-performance 2D-CFET integrations.

Antiferroelectrics are promising materials for applications in energy storage, solid-state cooling, and negative-capacitance devices. This study demonstrates that antiferroelectric-like behavior can be electrostatically engineered in ferroelectric superlattices. An electric field induces a reversible transition from a stable in-plane polarized state to a state with in-plane and out-of-plane polarized nanodomains that mimics, at the domain level, the nonpolar-to-polar transition of traditional antiferroelectrics.

Abstract

Antiferroelectric oxides are promising materials for applications in high-density energy storage, solid-state cooling, and negative capacitance devices. However, the range of oxide antiferroelectrics available today is rather limited. In this work, it is demonstrated that antiferroelectric properties can be electrostatically engineered in artificially layered ferroelectric superlattices. Using a combination of synchrotron X-ray nanodiffraction, scanning transmission electron microscopy, macroscopic electrical measurements, and lateral and vertical piezoresponse force microscopy in parallel-plate capacitor geometry, a highly reversible field-induced transition is observed from a stable in-plane polarized state to a state with in-plane and out-of-plane polarized nanodomains that mimics, at the domain level, the nonpolar to polar transition of traditional antiferroelectrics, with corresponding polarization-voltage double hysteresis and comparable energy storage capacity. Furthermore, it is found that such superlattices exhibit large out-of-plane dielectric responses without involving flux-closure domain dynamics. These results demonstrate that electrostatic and strain engineering in artificially layered materials offers a promising route for the creation of synthetic antiferroelectrics.

The twisted tungsten diselenide (WSe₂) bilayers stacked along with monolayer graphene exhibit noticeable room temperature ferroelectricity that decreases with twist angle within the range 0° < θ < 3°, and disappears completely for θ ≥ 4°. This variation aligns with moiré length scale-controlled ferroelectric dynamics (0° < θ < 3°), while loss beyond 4° may relate to twist-controlled commensurate to non-commensurate transitions. Also, 3° twisted WSe₂ exhibits ferroelectric and correlation-driven ferromagnetic ordering, indicating twist-controlled multiferroic behavior.

Abstract

Recently, researchers have been investigating artificial ferroelectricity, which arises when inversion symmetry is broken in certain R-stacked, i.e., zero-degree twisted, van der Waals (vdW) bilayers. Here, the study reports the twist-controlled ferroelectricity in tungsten diselenide (WSe₂) bilayers. The findings show noticeable room temperature ferroelectricity that decreases with twist angle within the range 0° < θ < 3°, and disappears completely for θ ≥ 4°. This variation aligns with moiré length scale-controlled ferroelectric dynamics (0° < θ < 3°), while loss beyond 4° may relate to twist-controlled commensurate to non-commensurate transitions. This twist-controlled ferroelectricity serves as a spectroscopic tool for detecting transitions between commensurate and incommensurate moiré patterns. At 5.5 K, 3° twisted WSe₂ exhibits ferroelectric and correlation-driven ferromagnetic ordering, indicating twist-controlled multiferroic behavior. The study offers insights into twist-controlled coexisting ferro-ordering and serves as valuable spectroscopic tools.

Fundamental mechanisms of droplet deposition in reactive inkjet printing are studied using copper metal-organic decomposition ink. The different deposition morphology of the copper ink at various temperatures is attributed to the generation of a localized seeding layer which attracts the copper ions to deposit. Understanding the deposition mechanism provides valuable guidance for printed functional devices using particle-free reactive inks.

Reactive inkjet (RIJ) printing represents an important approach for printed electronics. Different from the traditional inkjet printing of colloidal inks with nanosized metal particles, RIJ prints the solution of metal organic compound, that is, metal-organic decomposition (MOD) ink, and reduces it to the pure metal during the post-treatment to form conductive electrodes. Successful RIJ printing of MOD inks has been demonstrated; however, the fundamental understanding of droplet deposition involved in RIJ printing is lacking. Herein, the effect of substrate temperature and nozzle temperature during inkjet printing of copper MOD ink on the deposition morphology is investigated. It exhibits distinct behaviors in the deposition morphology at elevated temperatures when compared with the ones at room temperature. The different deposition morphology of the copper ink at various temperatures is attributed to the generation of a localized seeding layer which attracts the copper ions to deposit. In addition, the copper MOD ink printing is compared with a silver MOD ink. The different deposition morphology between the copper ink and silver ink is due to the solvent system. Understanding the deposition mechanism for reactive inks provides valuable information and guidance in the fabrication of printed functional devices using particle-free reactive inks.

Nature Nanotechnology, Published online: 26 September 2024; doi:10.1038/s41565-024-01792-1

Nature Nanotechnology, Published online: 26 September 2024; doi:10.1038/s41565-024-01788-x

Nature Nanotechnology, Published online: 26 September 2024; doi:10.1038/s41565-024-01791-2

Nature Physics, Published online: 24 September 2024; doi:10.1038/s41567-024-02629-3

The advances in boron-doped polycyclic aromatic hydrocarbons provide opportunities for single-molecule diodes since they promise unexplored p-type doped single-molecule devices. Here, we developed a combined break junction and van der Waals heterojunction methods to fabricate boron-doped single-molecule diodes in experiments. With such a strategy, the fabricated single-molecule diode achieved a rectification ratio as high as 457 at ±1 V.

Abstract

Single-molecule diode was the first proposed device in molecular electronics. Despite the great efforts and advances over 50 years, the reported rectification ratios, the most critical parameter of a diode, remain moderate for the single-molecule diode. Herein, we report an approach to achieve a larger rectification ratio by adopting the combined strategies of p-type boron doping, the single-layer graphene nodes, and the van der Waals layer-by-layer architecture. Measured current–voltage curves showed one of the as-fabricated single-molecule diodes hit an unprecedented large rectification ratio of 457 at ±1 V. Break junction operations and spectroscopic measurements revealed the three-atom-thick configuration of the single-molecule diodes. With the experimental and theoretical calculation results, we demonstrated the doped boron atoms induced holes to redistribute the electron density, making the asymmetric coupling at positive and negative biases, and the van der Waals interaction promoted asymmetric coupling and significantly boosted diode performance.

A magnetic barbell-shaped soft microrobot (MBS²M) is proposed inspired by the natural locomotion of crucian carp with the advantages of environmental adaptation, flexible movement, precise positioning, and multifunctionality. The proposed microrobot provides a “all-in-one” solution for sophisticated tasks in complex environments, which has excellent application potential and is expected to play an important role in biomedical applications such as drug delivery, detection, and diagnosis in vivo.

Abstract

The development of environmentally adaptive solutions for magnetically actuated microrobots to enable targeted delivery in complex and confined fluid environments presents a significant challenge. Inspired by the natural locomotion of crucian carp, a barbell-shaped soft microrobot (MBS²M) is proposed. A mechano-electromagnetic hybrid actuation system is developed to generate oscillating magnetic fields to manipulate the microrobot. The MBS²M can seamlessly transition between three fundamental locomotion modes: fast navigation (FN), high-precision navigation (HPN), and fixed-point rotation (FPR). Moreover, the MBS²M can move in reverse without turning. The multimodal locomotion endows the MBS²M's adaptability in diverse environments. It can smoothly pass through confined channels, climb over obstacles, overcome gravity for vertical motion, track complex pathways, traverse viscous environments, overcome low fluid resistance, and navigate complex spaces mimicking in vivo environments. Additionally, the MBS²M is capable of drug loading and release in response to ultrasound excitation. In an ex vivo porcine liver vein, the microrobot demonstrated targeted navigation under ultrasound guidance, showcasing its potential for specialized in vivo tasks.

Nature Photonics, Published online: 23 September 2024; doi:10.1038/s41566-024-01512-0

2D rhombohedral-phase ZnIn₂S₄ (R-ZIS) with controllable layer thickness is achieved by a confined-growth strategy in high yield. The correspondingly regulated electronic band structure and carrier dynamics result in continuously tunable optical absorption bands, photocarrier separation efficiency, self-powered capability, and dark current noise. Beneficial from such tunability, the high-performance self-powered broadband and deep-UV photodetectors are respectively achieved in multilayer and monolayer R-ZIS.

Abstract

2D materials with unique layer-dependent electronic structure can bring precise control to their photocarrier dynamics for optimizing and expanding optoelectronic applications, while the challenge of controlling layer stacking makes the layer dependency law still underexplored in emerging 2D ternary metal chalcogenides. Herein, 2D rhombohedral-phase ZnIn₂S₄ (R-ZIS) with controllable layer thickness is achieved by confined-growth strategy in high yield, exhibiting continuously tunable direct bandgap (2.39–2.77 eV) with evident upshift of conduction band minimum (CBM) and Fermi level (E _F), demonstrated arising from the synergistic effect of reduced interlayer interaction with inevitably increasing Zn defects. Remarkably, the carrier dynamics of R-ZIS in photoelectrochemical (PEC) device is successfully regulated by adjusted CBM and E _F, resulting in continuously tunable optical absorption band, photocarrier separation efficiency, self-powered capability, and dark current noise. Beneficial from tailored band structure and carrier dynamics, self-powered PEC-type photodetector with broadband photoresponse (254–765 nm), is achieved fast response speed (12.3/5.3 ms) and high responsivity (90.29 mA W⁻¹) in multilayer R-ZIS, while deep-UV photodetector with ultra-high specific detectivity (1.62 × 10¹² Jones) at 254 nm in monolayer R-ZIS, exhibiting the record performance in both fields. This work motivates the development of tailored band structure for 2D-materials-based optoelectronic devices in strategy and mechanism.

This review focuses on 2D multilayers, emphasizing their unique properties and advantages over monolayers for various applications. It begins with a discussion of the thickness-dependent properties of 2D materials and identifies applications where multilayers outperform monolayers. Additionally, the review covers wafer-scale growth of 2D multilayers and demonstrates their advantages in electronics and optoelectronics.

Abstract

2D materials possess significant potential across various applications, with physical and chemical properties that can be effectively modulated by their thickness, enabling tailored optimization for specific uses. For instance, 2D monolayers are ideal for transparent and flexible electronics, while 2D multilayers are more suitable for solar cells and high-speed devices. Although scalable methods for synthesizing large-area 2D materials and their applications have been developed, most research has focused on monolayers, with comparatively limited efforts directed toward multilayers. This review provides an overview of the emerging field of 2D multilayers, revisiting the analysis of layer-dependent properties to determine the optimal material thickness for various applications. It introduces representative techniques for synthesizing 2D multilayer films and presents applications where multilayer structures demonstrate superior performance compared to monolayers, particularly in electronics and optoelectronics. The review advocates for the development of synthesis and integration methods for 2D multilayers, calling for a shift in research focus toward these materials to enhance their technological impact and unlock new industrial applications.

This work presents a generalizable approach for the on-chip synthesis of non-layered, nanometer-thick, quasi-2D semimetals from multi-layer chalcogenides. In the exemplary case, sub-20 nm semiconducting InSe with nickel deposited on top are subjected to a low-temperature annealing step. This process enables a controlled transformation of the layered InSe into non-layered, crystalline Kagome-semimetal Ni₃In₂Se₂ via reaction with the laterally diffusing nickel.

Abstract

Reducing the dimensions of materials from three to two, or quasi-two, provides a fertile platform for exploring emergent quantum phenomena and developing next-generation electronic devices. However, growing high-quality, ultrathin, quasi2D materials in a templated fashion on an arbitrary substrate is challenging. Here, the study demonstrates a simple and reproducible on-chip approach for synthesizing non-layered, nanometer-thick, quasi-2D semimetals. In one implementation, this method starts with thin semiconducting InSe flakes of below 20 nm in thickness with nickel deposited on top, followed by a low-temperature annealing step that results in a controlled transformation of the layered InSe to a non-layered, crystalline semimetal via reaction with the laterally diffusing nickel. Atomic resolution microscopy reveals the transformed semimetal to be Ni₃In₂Se₂ with a Kagome-lattice structure. Moreover, it is demonstrated that this synthesis method is generalizable by transforming 2D layered chalcogenides such as SnS and SnSe employing Ni and Co to non-layered semimetals, paving the way for engineering novel types of devices.

Enhanced oxidation-resistance and multifunctionality in MXene Films are endowed with seamless heterostructure formation by sputtering a nano-thick copper layer onto the surface of MXene films. The resulting MXene@Cu films exhibit significantly improved resistance to oxidation, as well as enhanced electrical and mechanical properties, making them promising candidates for multifunctional applications in electromagnetic interference shielding and thermal management.

Abstract

MXene-based films have garnered significant attention for their remarkable electrical and mechanical properties. Nevertheless, the practical application of MXene is impeded by its intrinsic instability caused by spontaneous oxidation. The traditional anti-oxidative strategies frequently lead to a compromise in stability, electrical conductivity, and mechanical properties. In this study, a novel approach is proposed involving metal nano-armoring, wherein a copper layer with nano thickness is deposited onto MXene film surfaces to establish a uniform and seamless heterogeneous interface (MXene@Cu). The precise tunability and uniformity of this heterostructure are consistently demonstrated through both theoretical calculations and experimental results. The MXene@Cu films exhibit exceptional electrical conductivity of 1.17 × 10⁶ S m⁻¹, electromagnetic interference shielding effectiveness of 77.1 dB, and tensile strength of 43.4 MPa. More importantly, this heterostructure significantly improves MXene's stability against oxidation. After exposure to air for 30 days, the resultant MXene@Cu films exhibit a remarkable conductivity retention of 72.0%, significantly exceeding that of pristine MXene films (44.3%). This scalable synthesis approach holds significant promise for electronic device applications, particularly in electromagnetic shielding and thermal management.

This review covers recent progress in oxidized 2D transition metal dichalcogenides and their integration into other 2D materials in the form of van der Waals heterostructures. This review focuses on the new designer properties and functionalities that emerge through this integration, along with a critical outlook on promising next steps that will guide the focus and help advance the field.

Abstract

The surface oxidation of 2D transition metal dichalcogenides (TMDs) has recently gained tremendous technological and fundamental interest owing to the multi-functional properties that the surface oxidized layer opens up. In particular, when integrated into other 2D materials in the form of van der Waals heterostructures, oxidized TMDs enable designer properties, including novel electronic states, engineered light-matter interactions, and exceptional-point singularities, among many others. Here, the evolving landscapes of the state-of-the-art surface engineering technologies that enable controlled oxidation of TMDs down to the monolayer-by-monolayer limit are reviewed. Next, the use of oxidized TMDs in van der Waals heterostructures for different electronic and photonic device platforms, materials growth processes, engineering concepts, and synthesizing new condensed matter phenomena is discussed. Finally, challenges and outlook for future impact of oxidized TMDs in driving rapid advancements across various application fronts is discussed.