Jiuxiang Dai

npj 2D Materials and Applications, Published online: 07 April 2025; doi:10.1038/s41699-025-00551-7

This study presents an innovative approach to fabricating 2D Bi₂Te₃-Sb₂Te₃ chalcogenide superlattices in wrapped, lateral, and vertical configurations. Utilizing a novel precursor switching method, chemical vapor deposition, and post-growth techniques, the research achieves controlled superlattices with sharp interfaces. Comprehensive characterization and growth modeling provide insights into the formation of mechanisms and properties, opening avenues for advanced studies and potential applications.

Abstract

As a focal point in materials science, 2D superlattices, comprising periodically arranged nanostructures, have emerged as promising platforms for engineering, optoelectronic, and quantum phenomena. In this work, an innovative approach is studied to fabricate multi-layered 2D Bi₂Te₃-Sb₂Te₃ chalcogenide superlattices including wrapped, lateral and vertical ones. Using a novel precursor switching method, wrapped 2D van der Waals superlattices are synthesized via chemical vapor deposition. Thermal annealing and focused ion beam techniques are employed to achieve both lateral and vertical superlattices with controlled dimensions and sharp interfaces. Comprehensive structural and electronic characterization revealed the high crystalline quality and electronic properties of these superlattices. A comprehensive growth model is also developed to elucidate the growth mechanism and optimize the growth parameters. This research demonstrates a feasible approach to fabricate wrapped, lateral, and vertical superlattices, laying the foundation for further advanced study of their physical properties and potential device applications.

Achieving ultra-low subthreshold swing (SS) is crucial for energy-efficient electronics but remains constrained by the fundamental Boltzmann  thermionic limitation in conventional field-effect transistors (FETs). Here, a low-SS impact ionization FET is demonstrated based on a stepwise van der Waals WSe₂ homojunction, leveraging the impact ionization effect to enable sharp current transitions and high-gain switching. The device achieves an unprecedented SS of 3.09 mV dec⁻¹ at room temperature, further reducing to 0.25 mV dec⁻¹ at lower temperatures, with an on/off current ratio exceeding 10⁵ and an on-state current density of 1 µA µm⁻¹. This work provides a promising platform for next-generation low-power electronics.

Abstract

The low subthreshold swing (SS) below the Boltzmann thermionic limitation (60 mV dec⁻¹) is crucial for the development of power-efficient transistors. Recently, impact ionization field-effect transistors (II-FETs), which leverage carrier avalanche multiplication, have emerged as an attractive method for achieving ultra-steep SS, high on-state current density, and significant drain current on-off ratio. However, current II-FETs face challenges due to complex fabrication processes, hindering the development of future array devices. In this work, a novel II-FET is reported based on a stepwise van der Waals WSe₂ homojunction. The device exhibits a low SS of 3.09 mV dec⁻¹ and a high multiplication factor exceeding 10⁴ at room temperature. Additionally, by lowering the operating temperature, the SS can be further improved to 0.25 mV dec⁻¹. Along with the improved subthreshold characteristics, the device shows a current on/off ratio >10⁵ and an on-state current density of ~1 µA µm⁻¹. The findings presented here offer a promising approach to developing energy-efficient electronic devices for future technological generations.

This perspective provides a comprehensive review of recent advancements in the direct CVD synthesis of twisted graphene. It explores key progress in achieving precise twist angles, large domain sizes, and uniform distributions, while also addressing the underlying mechanisms. Future directions focus on scalable production, in situ monitoring, and twisted heterojunction to enable the integration of twisted graphene into quantum and optoelectronic applications.

Abstract

Twisted graphene, renowned for its exceptional physical properties such as insulating states, superconductivity, and the quantized anomalous Hall effect, represents a frontier in quantum materials research. Despite its transformative potential, the scalability of traditional “tear-and-stack” fabrication poses significant challenges, limiting widespread application. Recent advances in chemical vapor deposition (CVD) offer a promising alternative, enabling scalable synthesis of high-quality twisted graphene with advantages in cost, reproducibility, and tunable growth control. However, the fundamental mechanisms governing CVD growth, particularly the role of growth conditions and catalytic substrate in determining the size and twisted angle of twisted graphene, remain inadequately understood. This perspective explores recent progress in overcoming these challenges through dynamic modulation of the CVD growth environment and strategic substrate engineering, emphasizing their role in achieving precise twist angles, large size, and uniform twist angle distribution. By addressing these critical aspects, it is aimed to illuminate pathways for advancing the controlled growth of twisted graphene, facilitating its seamless integration into next-generation electronic, optoelectronic, and quantum technologies, and driving its transition from a laboratory curiosity to a scalable platform for technological innovation.

The PAA-assisted method is proposed to synthesize 4-inch carbon-free monolayer MoS₂ wafers, in which carboxy-rich linear polyacrylic acid (PAA) is selected as the skeleton to assist the uniform deposition of Mo ions. The quantitative and clean reactants are designed to solve the carbon residue problem in organic-mediated growth route and the wafer has high crystallinity and great improved electrical performance.

Abstract

Residues introduced are often underestimated and face challenges in purification during the material synthesis. For wafer-scale 2D transition metal dichalcogenides preparation, the organic-mediated growth route is favorable and optimal due to its precise controllability of source mass. However, the carbon residue generated from organic precursors severely damages the intrinsic electrical properties of the material. Especially for vapor organic source deposition approaches, the formation of amorphous carbon is almost inevitable due to the continuous introduction of gaseous organic sources. Here, a PAA-assisted strategy is developed to prepare carbon-free film by utilizing solid metalorganic sources and non-organic sulfur. The solid precursor blocks the supply of carbon and the sulfur further converts the remaining C into CS₂ to achieve effective elimination with a concentration below 1%. Carboxy-rich linear polyacrylic acid (PAA) is strategically selected as the organic skeleton and obtain a 4-inch carbon-free uniform MoS₂ wafer. The field-effect transistor arrays are fabricated and the devices exhibit a high carrier mobility of 13.3 cm²V⁻¹s⁻¹ with an ultra-low leakage current density. The PAA-assisted method provides a high-purity organic-mediated approach to efficiently synthesize high-quality MoS₂ wafers.

A novel PFOE Artificial Synapse integrating multimodal fusion perception in one device with a single functional material is presented, enabled by combined ferroelectricity (for synaptic behaviors), piezoelectricity (for tactile modulation), and optoelectronic responsiveness (for visual detection) of NbOI₂. Under the synergistic modulation of strain and light, visual-tactile fusion perception has been fully demonstrated, advancing multifunctional sensing devices for neuromorphic computing.

Abstract

Multimodal sensory integration is vital for the evolution of artificial intelligence, yet current approaches often rely on physically connecting distinct sensing units (such as visual and tactile devices) through external circuits, leading to data transmission delays and information loss. Here, a groundbreaking paradigm is demonstrated for integrating visual-tactile fusion perception in one device with a single functional material. This is achieved by developing an unprecedented 2D Piezo-Ferro-Opto-Electronic (PFOE) Artificial Synapse, which combines the comprehensive ferroelectricity (for synaptic behaviors), piezoelectricity (for tactile modulation), and optoelectronic responsiveness (for visual detection) of strained 2D NbOI₂. Under the synergistic influence of light and strain, the device exhibits remarkable persistent photoconductivity (PPC), a notable increase in paired-pulse facilitation (PPF) index (from 116% to 180%), and a reduction in the power exponent of the sublinear power-law fitting photocurrent curve (from 0.797 to 0.376). These features enhance the clarity and recognition of fingerprint images that integrate visual and tactile information. The work provides a robust foundation for integrating multisensory capabilities into advanced human-machine interfaces and artificial intelligence systems, marking a significant leap forward in the development of multifunctional neuromorphic devices.

Memristive semiconductor H_xNa_2-xIn₂As₃ exhibits memristive switching and maintains semiconductor properties through ion migration in its vdW gaps. Low ion migration energy enables a low set voltage, while its low-symmetry structure produces anisotropic ion transport, offering insights into directional dependence. These findings can guide the development of energy-efficient memtransistors.

Abstract

The use of the van der Waals (vdW) gap as an ion migration path, similar to cathode materials in lithium-ion batteries, enables improved ion migration. If these materials also possess semiconductor properties, they can simultaneously control electron or hole transport. Such materials can be used in memtransistors, which combine memory and semiconductor characteristics. However, the existing materials rely on defects such as grain boundaries as migration paths, resulting in high ion migration energy barriers and switching voltages. Herein, memtransistors are demonstrated using H_xNa_2-xIn₂As₃, which utilizes the vdW gap for ion migration, resulting in lower ion migration energy barriers. It is confirmed that ion migration occurs more readily in the [010] direction in a low-symmetry crystal structure owing to a lower migration energy barrier, whereas migration does not occur in the [100] direction, demonstrating directional dependence. This finding provides crucial guidelines for identifying ion migration in semiconductor materials, which can otherwise be overlooked. The use of the vdW gap as the migration path, variation in migration energy barriers with the ion movement direction, and their impact on low power consumption are critical factors that will guide the future development of memtransistor materials.

Nature Chemistry, Published online: 07 April 2025; doi:10.1038/s41557-025-01797-w

npj 2D Materials and Applications, Published online: 07 April 2025; doi:10.1038/s41699-025-00548-2

Janus MoSSe nanotubes exhibit unique properties and demonstrate lower strain energy than their corresponding Janus monolayer counterparts when the diameter exceeds 40 Å. In this work, Janus MoSSe nanotubes are successfully synthesized from MoS₂ nanotubes using H₂ plasma at room temperature. The formation of the Janus structure is confirmed through Raman spectroscopy and microscopy characterization, enabling further exploration of their novel properties.

Abstract

Two-dimensional (2D) Janus transition metal dichalcogenide (TMDC) layers with broken mirror symmetry exhibit giant Rashba splitting and unique excitonic behavior. For their one-dimensional (1D) counterparts, the Janus nanotubes possess curvature, which introduces an additional degree of freedom to break the structural symmetry. This can potentially enhance these effects or even give rise to novel properties. Moreover, Janus MSSe nanotubes (M = W, Mo), with diameters surpassing 40 Å and Se positioned externally consistently demonstrate lower energy states compared to their Janus monolayer counterparts. However, there are limited studies on the preparation of Janus nanotubes, due to the synthesis challenge and limited sample quality. In this study, we first synthesized MoS₂ nanotubes on single-walled carbon nanotube (SWCNT) and boron nitride nanotube (BNNT) heterostructures and then explored the growth of Janus MoSSe nanotubes from MoS₂ nanotubes at room temperature with the assistance of H₂ plasma. The successful formation of the Janus structure is confirmed by Raman spectroscopy, and atomic structure and elemental distribution of the grown samples are further characterized by advanced electronic microscopy. The synthesis of Janus MoSSe nanotubes based on SWCNT-BNNT heterostructures paves the way for further exploration of novel properties in Janus TMDC nanotubes.

Residue-free 2D materials with exceptional cleanliness and high quality are achieved using van der Waals interaction-based fabrication and manipulation techniques, completely free from polymers and solvents. Precise manipulation enables the construction of vdW heterostructures with controlled alignment, expanding the potential of 2D materials for next-generation electronic and optoelectronic devices.

Abstract

2D materials have garnered considerable attention due to their distinctive properties, prompting diverse applications across various domains. Beyond their inherent qualities, the significance of 2D materials extends into the fabrication processes that can lead to the degradation of intrinsic performance through undesirable mechanical defects and surface contaminations. Herein, a novel fabrication technique to achieve residue-free 2D materials using van der Waals (vdW) interactions, primarily employing molybdenum disulfide (MoS₂) is proposed. Optical and electrical characterizations confirm the absence of residues, mechanical defects, oxidation, and strain, along with a prominent field-effect mobility of up to 60 cm² V⁻¹ s⁻¹ and an on/off ratio of ≈10⁸. Furthermore, the utilization of residue-free material as a stamp enables various manipulations of flakes transferred on substrates in advance, including pick-up and release, stacking, exfoliation, wiping-out, flipping, and smoothing-out processes. Additionally, the manipulation techniques also facilitate the fabrication of vdW heterostructures with precise positioning and the desired stacking order. In this regard, the feasibility of applying this method to hexagonal boron nitride and graphite is demonstrated. It is expected that this method will offer a versatile and effective approach to enhancing the qualities of 2D material-based electronic and optoelectronic devices.

Nature Photonics, Published online: 03 April 2025; doi:10.1038/s41566-025-01656-7

Nature, Published online: 03 April 2025; doi:10.1038/s41586-025-08954-8

A significant change in the local piezoelectric potential is observed in a monolayer hBN after the introduction of defects. Further high-throughput molecular dynamics simulations also show a continuous decrease or even increase in the piezoelectric coefficients of 2D hBN by properly designing defect structures. To inversely design defective 2D hBN with specific piezoelectric properties, a machine learning-based method is proposed.

Abstract

Piezoelectricity in 2D hexagonal boron nitride (hBN) plays a crucial role in its applications in various advanced functional devices. Therefore, appropriately adjusting intrinsic piezoelectric properties of 2D hBN becomes desirable for different advanced piezoelectric applications. Herein, using the Kelvin probe force microscope, it is directly found that local piezoelectric potentials of monolayer hBN can be enhanced by ≈20% after the introduction of defects. High-throughput molecular dynamics simulations on hundreds of thousands of defective 2D hBN structures further show a continuous decrease or even increase in piezoelectric coefficients by properly designing the defect structures. The tunability of piezoelectricity in defective 2D hBN is found to be mainly attributed to flexoelectric effects around defects, which can increase or reduce the polarization in stretched defective 2D hBN by over 50%. To inversely design defective 2D hBN structures with specific piezoelectric properties, a machine learning-based method is proposed. Besides hBN, the proposed defect engineering strategy also has the capacity to be extended to tailor the piezoelectric properties of other 2D materials, such as molybdenum disulfide. This work not only expands the understanding of piezoelectricity in defective 2D hBN but also offers a novel approach to designing the piezoelectric property of 2D materials via defect engineering.

Nature Materials, Published online: 04 April 2025; doi:10.1038/s41563-025-02200-2

Ultrathin In₂O₃ films are prepared by exfoliating the oxide skins from liquid indium. The indium metal residue introduces autonomous metal-semiconductor junctions self-embedded within the In₂O₃ films after post-annealing, facilitating strong coupling between highly active gas-solid interaction and thermionic-emission-dominated electron transportation, which results in rapid, sensitive, and highly selective hydrogen gas sensing at room temperature.

Abstract

Semiconductor-based hydrogen sensors provide cost-efficient solutions for safety and a circular hydrogen-based economy. Liquid metal-derived 2D metal oxides show promise as ultrathin sensing materials. However, conventional exfoliation inevitably introduces metallic resides, which are often removed post-synthesis. Here the residual indium nano-islands are strategically retained within annealed 2D ultrathin In₂O₃ layers, creating self-embedded Schottky junctions. This unique architecture enhances gas-solid coupling at In/In₂O₃ interfaces. Tuning the composition and spatial distribution of the indium nano-islands amplifies the thermionic electron emission across the Schottky barriers. The resulting sensor achieves room-temperature hydrogen detection with a rapid response time of 4.4 s, high sensor response of 3.4, and >2.5 selectivity against common interferents. Remarkably, it exhibits only a 6.7% performance deviation after 6 weeks and shows good humidity resistance. These merits underscore the potential of the material and method for addressing the formidable challenge in developing room-temperature high-performance hydrogen sensors.

npj 2D Materials and Applications, Published online: 06 April 2025; doi:10.1038/s41699-025-00550-8

Publication date: July 2025

Source: Materials Today, Volume 86

Author(s): Cong Wang, Menghan Wu, Muqing Li, Yingcan Zhao, Mingchuang Zhao, Yunhao Zhang, Yichao Bai, Jianxiang Gao, Xiaoxia Wang, Xilin Tian, Han Zhang, Liang Chang, Xiaolong Zou, Bilu Liu, Feiyu Kang, Mauricio Terrones, Yu Lei

The nonstoichiometric VO _x exhibits a distinct ferromagnetic hysteresis loop and demonstrates a high magnetic susceptibility (χ=dMdH$ = \frac{{dM}}{{dH}}\;$∼10). Micromagnetic simulations show the results of the “partial volume fraction ferromagnetic phase model” for VO _x /Co/Pt structure. Experimental observed noncollinear spin structure in Co can be qualitatively explained by the exchange coupling between a small volume fraction of the ferromagnetic phase of VO _x and Co layer.

Abstract

Vanadium oxide (VO _x ) is a material of significant interest due to its metal-insulator transition (MIT) properties as well as its diverse stable antiferromagnetism depending on the valence states of V and O with distinct MIT transitions and Néel temperatures. Although several studies reported ferromagnetism in the VO _x , it is mostly associated with impurities or defects, and pure VO _x has rarely been reported as ferromagnetic. The research presents clear evidence of ferromagnetism in the VO _x thin films, exhibiting a saturation magnetization of ≈13 kA m⁻¹ at 300 K. The 20-nm thick VO _x thin films via reactive sputtering from a metallic vanadium target in various oxygen atmospheres is fabricated. The oxidation states of ferromagnetic VO _x films show an ill-defined stoichiometry of V₂O_{3+ p} , where p = 0.05, 0.23, 0.49, with predominantly disordered microstructures. The ferromagnetic nature of these VO _x films is confirmed through a strong antiferromagnetic exchange coupling with the neighboring ferromagnetic layer in the VO _x /Co bilayers, in which the spin configurations of the Co layer is influenced strongly due to the additional anisotropy introduced by VO _x layer. The present study highlights the potential of VO _x as an emerging functional magnetic material with tunability by oxidation states for modern spintronic applications.

Light: Science & Applications, Published online: 02 April 2025; doi:10.1038/s41377-025-01788-z

Nature Photonics, Published online: 21 March 2025; doi:10.1038/s41566-025-01633-0

Nature, Published online: 02 April 2025; doi:10.1038/s41586-025-08759-9

Nature Materials, Published online: 02 April 2025; doi:10.1038/s41563-025-02196-9

Nature Materials, Published online: 02 April 2025; doi:10.1038/s41563-025-02168-z

Nature Materials, Published online: 01 April 2025; doi:10.1038/s41563-025-02178-x

Nature Materials, Published online: 01 April 2025; doi:10.1038/s41563-025-02201-1

Nature Materials, Published online: 01 April 2025; doi:10.1038/s41563-025-02193-y