Jiuxiang Dai

The fabrication of a wafer-scale self-aligned MoS₂ FETs array is presented, with gate and channel lengths scaling simultaneously. High-performance devices have been achieved through the optimization of contact and dielectric. Logic modules and devices with 200 nm channel length demonstrate the process's feasibility and scalability, which provides a pathway for 2D materials in miniaturization and integration.

Abstract

Two-dimensional semiconductor materials (2DSM) effectively mitigate the short-channel effect due to their atomic thickness, offering significant advantages over traditional silicon-based materials, particularly in short channel length. In manufacturing 2DSM top-gate field-effect transistors (TG-FETs), simultaneous miniaturization of the gate and channel can only be achieved through a self-alignment process, enabling high-density integration of short-channel FETs. However, current self-aligned FETs based on 2DSM face challenges in attaining wafer-scale integration due to manufacturing process limitations. This work has successfully developed high-performance and wafer-scale TG-FET arrays using a self-aligned method that integrates the processes of dry etching, wet selective etching, and post-device optimization. The miniaturization is demonstrated by fabricating TG-FETs with a channel length of 200 nm, achieving an impressive on-state current density of 465.5 µA µm⁻¹ and a high on-off current ratio of 10⁸. Furthermore, we constructed the inverters and logic modules based on self-aligned FETs, showcasing the process's compatibility for future integration.

Author(s): Ri He, Hua Wang, Fenglin Deng, Yuxiang Gao, Bingwen Zhang, Yubai Shi, Run-Wei Li, and Zhicheng Zhong

Two-dimensional van der Waals materials, possessing a unique stacking degree of freedom, offer an alternative strategy for modulating their properties through interlayer sliding. Controlling the stacking order is crucial for tuning material properties and developing slidetronics-based devices. Here,…

[Phys. Rev. Lett. 134, 076101] Published Wed Feb 19, 2025

2D materials, with their high specific surface area and tunable surface characteristics, serve as ideal templates for studying surface-dependent gas adsorption phenomenon. Here, the mechanisms for gas adsorption on modified 2D surfaces are discussed and insights that can lead to further advancements for developing ultrafast gas sensors for applications such as environmental monitoring and industrial use are presented.

Abstract

Owing to their exceptional characteristics, such as one-atom thickness, high specific surface area, and tunability of surfaces, 2D materials are excellent templates to study the surface-dependent gas adsorption phenomenon. Moreover, the properties of 2D materials like morphology, bandgap, structure, and carrier mobility can be modulated easily by modification methods such as functionalization, defect and doping engineering. These modifications create and activate unconventional inert and active sites, leading to the selective adsorption of gases via mechanisms such as charge transfer kinetics, Schottky-barrier modification, and surface interactions. These methods enhance the adsorption sites by adding covalent and non-covalent moieties to the 2D surface and play a critical role in developing ultrafast gas sensing with high sensitivity, selectivity, fast response/recovery rates, and low detection limits. Here, this perspective is presented on the mechanism of the adsorption process of gases on modified 2D surfaces based on recent studies related to adsorption-dependent applications of 2D materials.

This review highlights advances in micro/nanorobots-enabled light-based biosensing and imaging. Untethered and remotely controlled micro/nanorobots enable precision biosensing using colorimetric and surface-enhanced Raman spectroscopy methods. They also provide cutting-edge in vitro intracellular and in vivo bioimaging in complex biological environments and organs. Furthermore, micro/nanorobots facilitate the development of point-of-care optical biosensors, enhancing disease diagnosis and prognosis capabilities in medical applications.

Abstract

Sensing and imaging of biomolecules are crucial to disease diagnosis, prognosis, and therapy where optical techniques have essential utility. Untethered and remotely controlled micro/nanorobots have shown promising sensing and imaging capabilities, especially in complex biological environments. In this review, how micro/nanorobots are used for optical biosensing and imaging while highlighting the significant developments in the field is discussed. Starting is done by exploring colorimetric biosensing methods enabled by micro/nanorobots. Significant advancements in surface-enhanced Raman spectroscopy-integrated micro/nanorobots are reviewed. Further, state-of-the-art optical bio-imaging applications by micro/nanorobots at in vitro intracellular level are highlighted. Novel in vivo bio-imaging assisted by optical micro/nanorobot sensors is examined. Furthermore, innovations in micro/nanorobots are assessed where motion augmentation is used as a detection mechanism, with applications in point-of-care molecular diagnostics. Finally, the challenges associated with micro/nanorobots-assisted advanced optical biosensing and imaging while discussing insights about potential research directions for this rapidly progressing field are summarized.

Au substrate induces a strain in the adhered bottommost MoS₂ layer. The strain weakens the coupling at the first MoS₂-MoS₂ interface, making it the weakest point in the system, therefore MoS₂ crystal preferentially cleaves at this interface, facilitating the selective exfoliation of large-area monolayers with size comparable to that of the parent crystal.

Abstract

Gold-assisted exfoliation (GAE) is a groundbreaking mechanical exfoliation technique that produces centimeter-scale single-crystal monolayers of 2D materials. Such large, high-quality films offer unparalleled advantages over the micron-sized flakes typically produced by conventional exfoliation techniques, significantly accelerating the research and technological advancements in the field of 2D materials. Despite its wide applications, the fundamental mechanism of GAE remains poorly understood. In this study, using MoS₂ on Au as a model system, ultra-low frequency Raman spectroscopy is employed to elucidate how the interlayer interactions within MoS₂ crystals are impacted by the gold substrate. The results reveal that the coupling at the first MoS₂-MoS₂ interface between the adhered layer on the gold substrate and the adjacent layer is substantially weakened, with the binding force being reduced to nearly zero. This renders the first interface the weakest point in the system, thereby the crystal preferentially cleaves at this junction, generating large-area monolayers with sizes comparable to the parent crystal. Biaxial strain in the adhered layer, induced by the gold substrate, is identified as the driving factor for the decoupling effect. The strain-induced decoupling effect is established as the primary mechanism of GAE, which can also play a significant role in general mechanical exfoliations.

Nature, Published online: 19 February 2025; doi:10.1038/s41586-024-08492-9

Red, green, and blue (R/G/B) colored 2D perovskite nanocrystals synthesized via an ultrasonic spray method demonstrate outstanding photo-detection performance in 4-inch photodetector arrays with a 100% operational yield, enabled by a liquid-bridge-transport strategy. This scalable, self-aligned synthesis provides a practical pathway for high-performance, large-area perovskite optoelectronic devices and shows promising potential for broader applications in integrated optoelectronic systems.

Abstract

2D perovskite (PVSK) single crystals have received significant attention due to their unique optical and optoelectronic properties. However, current synthesis methods face limitations, particularly in large-area fabrication, which remain critical barriers to practical applications. In this study, the synthesis of red/green/purple-blue-colored 2D PVSK nanocrystals over a large area (4-inch wafer) and the fabrication of high-performance photodetector arrays are presented via a facile yet efficient spray-coating approach with a liquid-bridge transport effect. The photodetector array achieves 100% working yield, high photo-responsivity (1.5 × 10⁶ A W⁻¹) and specific-detectivity (1.1 × 10¹⁶ Jones) with competitive photomapping characteristics. An intelligent vision system for automatic shape recognition is further demonstrated with a recognition rate exceeding 90%. This study provides significant advances in the scalable synthesis of nanoscale 2D PVSK crystals, their integration into large-area optoelectronic devices, and their potential use in artificial-intelligence systems.

Author(s): L. L. Tao, Mingbo Dou, Xianjie Wang, and E. Y. Tsymbal

In ferroelectric (FE) semiconductors with strong spin-orbit coupling, the electron’s spin direction is locked to its momentum by an intrinsic spin-orbit field (SOF) switchable by ferroelectric polarization. This provides a promising platform for novel nonvolatile spintronic devices. Here, we propose…

[Phys. Rev. Lett. 134, 076801] Published Wed Feb 19, 2025

npj 2D Materials and Applications, Published online: 19 February 2025; doi:10.1038/s41699-025-00536-6

The study provides a Si-CMOS compatible approach to synthesize 2D wafer-scale 1T-CrTe₂ films. Magnetic property measurements reveal that the synthesized 1T-CrTe₂ films exhibit room-temperature magnetism, perpendicular magnetic anisotropy, and distinct step-like magnetic transitions. Moreover, the study highlights how unintentional adsorbents or dopants can significantly influence the magnetic behaviors of such 1T-CrTe₂ films.

Abstract

2D room-temperature ferromagnet CrTe₂ is a promising candidate material for spintronic applications. However, its large-scale and cost-effective synthesis remains a challenge. Here, the fine controllable synthesis of wafer-scale 1T-CrTe₂ films is reported on a SiO₂/Si substrate using plasma-enhanced chemical vapor deposition at temperatures below 400 °C. Magnetic hysteresis measurements reveal that the synthesized 1T-CrTe₂ films exhibit perpendicular magnetic anisotropy along with distinct step-like magnetic transitions. It is found that 1T-CrTe₂ is susceptible to oxygen adsorption even in ambient conditions. The theoretical calculations indicate that the oxidation of surface layers is crucial for the absence of out-of-plane easy axis in few-layer CrTe₂, while the interlayer antiferromagnetic coupling among the upper surface layers leads to the observed step-like magnetic transitions. The study provides a Si-CMOS compatible approach for the fabrication of magnetic 2D materials and highlights how unintentional adsorbents or dopants can significantly influence the magnetic behaviors of these materials.

This study explores ultrathin epitaxial La₂Ti₂O₇ films, a layered perovskite from the Carpy-Galy family, grown on various substrates. Remarkably, high epitaxial strain promotes layer-by-layer growth and stabilizes the correct phase. The films exhibit a polarization significantly higher than previously reported, exceeding 18 µCcm⁻², and retain ferroelectricity down to a single-unit-cell thickness, highlighting their potential for advanced nanoscale devices.

Abstract

Layered perovskite-based compounds offer a range of unconventional properties enabled by their naturally anisotropic structure. Among these, the Carpy-Galy phases (A _n B _n O_3n+2), characterized by (110)-oriented perovskite planes interleaved with additional oxygen layers, stand out for robust in-plane polarization. However, the challenges associated with the synthesis of ultrathin Carpy-Galy films and understanding the impact of strain on their properties limit their integration into devices. Here, La₂Ti₂O₇ (n = 4) films grown on substrates imposing tensile, compressive, or negligible epitaxial strains are investigated. Surprisingly, a 3% tensile strain from DyScO₃ (100) substrates facilitates layer-by-layer growth mode, whereas compressive (LaAlO₃-Sr₂TaAlO₆ (110)) or negligible (SrTiO₃ (110)) epitaxial strains require post-deposition annealing to reach comparable crystallinity. Using density-functional theory calculations, scanning probe microscopy, X-ray diffraction, scanning transmission electron microscopy, and polarization switching experiments, it is confirmed that these films possess exceptional ferroelectric properties, including a polarization of 18 µCcm⁻² – more than three times higher than previously reported – as well as persistence of ferroelectricity down to a single-unit-cell thickness. This study not only advances the understanding of Carpy-Galy phases as epitaxial thin films but also lays a foundation for their integration into advanced ferroelectric device architectures.

Owing to their atomic-scale thickness and dangling-bond-free surfaces, 2D materials have become promising alternatives for electronic devices operating at high temperatures. This review comprehensively summaries the recent progresses on the interface engineering of 2D materials toward high-temperature electronic devices, including FETs, optoelectronic devices, sensors, and neuromorphic devices.

Abstract

High-temperature electronic materials and devices are highly sought after for advanced applications in aerospace, high-speed automobiles, and deep-well drilling, where active or passive cooling mechanisms are either insufficient or impractical. 2D materials (2DMs) represent promising alternatives to traditional silicon and wide-bandgap semiconductors (WBG) for nanoscale electronic devices operating under high-temperature conditions. The development of robust interfaces is essential for ensuring that 2DMs and their devices achieve high performance and maintain stability when subjected to elevated temperatures. This review summarizes recent advancements in the interface engineering of 2DMs for high-temperature electronic devices. Initially, the limitations of conventional silicon-based materials and WBG semiconductors, alongside the advantages offered by 2DMs, are examined. Subsequently, strategies for interface engineering to enhance the stability of 2DMs and the performance of their devices are detailed. Furthermore, various interface-engineered 2D high-temperature devices, including transistors, optoelectronic devices, sensors, memristors, and neuromorphic devices, are reviewed. Finally, a forward-looking perspective on future 2D high-temperature electronics is presented. This review offers valuable insights into emerging 2DMs and their applications in high-temperature environments from both fundamental and practical perspectives.

Single crystal microcavity organic light-emitting diodes (SC-MC-OLEDs) with high color purity (FWHM < 10 nm), high brightness (> 10⁶ cd m⁻²), high efficiency (EQE∼4%), high polarization (> 0.90) and high stability are realized by combining the large size 2D organic single crystals with efficient microcavity effect, unlocking potential for ultra-high-definition displays and AR/VR applications.

Abstract

The development of ultra-high-definition (UHD) displays demands organic light-emitting diodes (OLEDs) with high color purity of all three primary colors for a wide color gamut and high brightness essential for future AR/VR applications. However, the vibronic coupling in organic emitters typically results in broad emissions, with a full width at half maximum (FWHM) exceeding 40–50 nm. Herein, multicolor organic single-crystal microcavity light-emitting diodes (SC-MC-OLEDs) are demonstrated by embedding ultrathin 2D organic single crystals (2D-OSCs) between two silver layers that serve as both electrodes and mirrors. By leveraging the microcavity effect, the resonant output frequencies of SC-MC-OLEDs can be continuously tuned from 448 to 602 nm by adjusting the thickness of 2D-OSCs (i.e., the microcavity length), achieving high color purity with a full width at half maximum (FWHM) of <10 nm. Furthermore, the Purcell effect in SC-MC-OLEDs enhances the radiative rate and improves light-coupling efficiency, resulting in a maximum external quantum efficiency (EQE) of up to 4% and minimal efficiency roll-off. Due to the excellent bipolar transport properties of OSCs, the brightness of SC-MC-OLEDs surpasses 10⁶ cd m⁻², along with a degree of linear polarization exceeding 0.9, unlocking new application opportunities.

A T-In₂Se₃/M-WS₂/B-WSe₂ heterojunction photodetector is proposed, boasting pronounced gate-tunability, achieving remarkable light on/off ratio and detectivity of at V _gs = −25 V, alongside competitive responsivity and gain at V _gs = 30 V. Leveraging this device as the pivotal sensing component, proof-of-concept applications spanning broadband optoelectronic imaging and automatic driving are demonstrated.

Abstract

Taking advantage of their unparalleled electrostatic and optoelectronic properties, 2D layered materials (2DLMs) have emerged as alluring building blocks for crafting advanced photodetectors. Nevertheless, preceding research has predominantly concentrated on rudimentary designs incorporating single-channel or single-junction setups, failing to exert the full potency of 2DLMs. Therefore, there is still an imperative requirement to develop innovative device architectures grounded in novel physical mechanisms. Herein, a T-In₂Se₃/M-WS₂/B-WSe₂ heterojunction photodetector boasting pronounced gate-tunability is devised, achieving remarkable light on/off ratio of 5.8 × 10⁴ and detectivity of 1.1 × 10¹³ Jones at V _gs = −25 V, alongside competitive responsivity and gain of 633 A W⁻¹ and 1943 at V _gs = 30 V. Energy band analysis has determined that the former is associated with the synergy of the cascaded band alignment and the high degree of depletion effect, while the latter is ascribed to the intermediate electron reservoir enabling high-efficiency spacial separation of photoexcited electron−hole pairs. Leveraging this device as the pivotal sensing component, proof-of-concept applications spanning broadband optoelectronic imaging and automatic driving are demonstrated. This study presents a novel paradigm for constructing 2DLM-based photodetectors with outstanding comprehensive performance, thereby establishing a fascinating platform capable of catering to the diverse demands of next-generation optoelectronic industry.

Through the one-pot interface-enhanced selenization and self-guided growth method, wafer-scale HfSe₂/WSe₂ interlayer heterostructures with vertically aligned van der Waals layers are fabricated. The resulting heterostructures, characterized by covalent bonds, demonstrate significant charge transfer, enhanced piezoelectricity, notable rectification effects, and Si-compatible transistor integration.

Abstract

2D heterostructures have garnered significant interest in the scientific community owing to their exceptional carrier transport properties and tunable band alignment. The fabrication of these heterostructures on a wafer scale is crucial for advancing industrial applications but remains particularly challenging for metals with low sulfidation activity, such as Hf. Herein, the one-pot method is developed for fabricating wafer-scale HfSe₂/WSe₂ interlayer heterostructures with vertically aligned van der Waals layers via interface-enhanced selenization and self-guided growth. By depositing a W layer (high sulfidation activity) over a Hf layer, followed by a one-pot selenization process, the chemical combination between Hf and Se atoms is enhanced through interfacial Se diffusion and confined lattice reaction. Moreover, the WSe₂ layers grow perpendicular to the substrate and further guide the crystallization of the bottom HfSe₂ layers. The resulting heterostructures, characterized by covalent bonds, demonstrate significant charge transfer, enhanced piezoelectricity, notable rectification effects, and Si-compatible transistor integration. This interface-enhanced selenization and self-guided growth pathway may provide valuable insights into the fabrication of covalently connected interlayer heterostructures involving metals with low sulfidation activity, as well as the development of high-density integrated circuits.

This research presents LAX phases, innovative layered materials from late transition metals, as alternatives to MAX phases. Using crystal structure prediction and machine learning, we identified 207 stable LAX systems with superior mechanical properties. These findings open pathways for LXene synthesis, promising advancements in catalysis and materials innovation, and highlight the vital role of scientific exploration in shaping a sustainable future.

Abstract

Ternary MAX phases, characterized by the chemical formula M₂AX, represent a group of layered materials with hexagonal lattices. These MAX phases have been the subject of extensive experimental and theoretical studies. Formation energy and thermodynamic calculations indicate that MAX phases containing late transition metals, such as Rh, Ru, Pt, Pd, Co, and Ni, are unlikely to form. Here, we introduce an alternative family of orthorhombic and monoclinic materials, the LAX phases, which exhibit similarities to MAX phases in terms of their layered structure and A and X elements. However, LAX materials incorporate late transition metals in place of the early transition metals. Advanced techniques for predicting the crystal structure of materials, coupled with data-driven materials research and machine learning algorithms, were employed to investigate the stable structures containing transition metals from the last groups of the d-block elements. The analyses revealed 207 ternary LAX systems that demonstrate robust stability against decomposition, with 100 of these systems showing dynamic stability. An in-depth examination of the top 10 structures revealed five LAX systems that are phase stable and exhibit superior mechanical properties, outperforming MAX phase counterparts in Young's modulus, stiffness, and hardness. These findings indicate that many LAX phase structures are viable candidates for future synthesis, highlighting the potential of heuristic-based structure searches in material discovery.

npj 2D Materials and Applications, Published online: 17 February 2025; doi:10.1038/s41699-024-00506-4

Sr_{2- x} Ga₂GeO₇: x Tb³⁺ (0 mol%  ≤ x ≤ 10 mol%) phosphors with persistent luminescence are synthesized via a high-temperature solid-state reaction. The phosphor exhibited a 4.99 eV direct band gap, ≈7000 s luminescence lifetime, and 100 s afterglow. Defects enhanced luminescence. Applications include latent fingerprint detection and anticounterfeiting.

Abstract

A series of Sr_2-xGa₂GeO₇: x Tb³⁺ (0 mol%  ≤ x ≤ 10 mol%) phosphors exhibiting persistent luminescence is synthesized via a high-temperature solid-state reaction. Structural analysis and phase identification are conducted using X-ray powder diffraction and Rietveld refinement. The reflectance spectra revealed that the synthesized phosphor exhibited a direct bandgap with a value of 4.99 eV.  The photoluminescence excitation spectra displayed broad absorption bands corresponding to the 4f₈ → 4f₇5d₁ transition of the Tb³⁺ ion, along with narrow-band absorption peaks attributed to the 4f-4f transitions. The emission spectra featured peaks resulting from transitions from the excited energy-state (⁵D₃/⁵D₄) to the ground-state levels (⁷F_J). Among these transitions, the ⁵D₄ → ⁷F₅ transition is dominant, producing the green emission of the synthesized phosphor. Concentration quenching is observed, attributed to the radiative reabsorption process. Additionally, the synthesized phosphor demonstrated thermal stability up to 675 K. The kinetic scan and afterglow measurements showed that the persistent luminescence lifetime is ≈7000 s, and the afterglow persistence is up to 100 s. Thermoluminescence measurements revealed that besides the intrinsic defect, doping introduced the interstitial and vacancy defects that contributed to improving the persistent luminescence of the synthesized phosphor. The synthesized phosphor demonstrated a practical application for latent fingerprint detection and anticounterfeiting applications.

Single photon emitters (SPEs) lie at heart of quantum technologies. It is shown that ultralow energy electron beam (5 keV) irradiation can create SPEs in monolayer MoS₂. Spatially deterministic creation of SPEs with 50 nm accuracy using electron beam lithography is then demonstrated. This is a disruptive technology for creating SPEs, and can enable fundamental physics concerning defect-defect coupling and electron–matter interactions.

Abstract

Single photon emitters (SPEs) are building blocks of quantum technologies. Defect engineering of two-dimensional (2D) materials is ideal to fabricate SPEs, wherein spatially deterministic and quality-preserving fabrication methods are critical for integration into quantum devices and cavities. Existing methods use combination of strain and electron irradiation, or ion irradiation, which make fabrication complex, and limited by surrounding lattice damage. Here, only ultra-low energy electron beam (e-beam) irradiation (5 keV) is utilized to create dilute defect density in hBN-encapsulated monolayer MoS₂, with ultra-high spatial resolution (<50 nm, extendable to 10 nm). Cryogenic photoluminescence spectra exhibit sharp defect peaks, following power-law for finite density of single defects, and characteristic Zeeman splitting for MoS₂ defect complexes. The sharp peaks have low spectral jitter (<200 µeV), and are tunable with gate-voltage and e-beam energy. Use of low-momentum electron irradiation, ease of processing, and high spatial resolution, will disrupt deterministic creation of high-quality SPEs.

In this work, the controllable growth of monocrystalline MoS₂/polycrystalline ReS₂ lateral heterojunctions are provided via a two-step chemical vapor deposition method based on the systematically analysis of the competition between vertical stacking and lateral epitaxy. The as-grown lateral heterojunctions are then fabricated into photodetectors, revealing a responsivity and an external quantum efficiency of 2.65 A W⁻¹ and 506%, respectively.

Abstract

Photodetectors (PDs) based on 2D transition metal dichalcogenides (2D TMDCs) heterojunction have become a potential candidate for frontier technology applications such as visible light communication (VLC). However, the conventional 2D TMDCs heterojunction PDs are facing problems with excessive dark current and low photoelectric conversion efficiency, resulting in the performance of PDs not meeting application requirements. Herein, the controllable growth of monocrystalline MoS₂/polycrystalline ReS₂ lateral heterojunction via a two-step chemical vapor deposition (CVD) method has been proposed. According to the result of density functional theory (DFT) calculation and the characterization of multiple parallel experiments under different conditions, the controllable growth of lateral heterojunction, especially the competition mechanism between lateral epitaxy and vertical stacking is systematically analyzed from different perspectives. Based on the analysis above, a strategy for preparing monocrystalline MoS₂/polycrystalline ReS₂ lateral heterojunction with a large-scale epitaxy layer and a high-quality lateral structure is provided. Finally, PDs based on the as-grown lateral heterojunction with responsivity and external quantum efficiency (EQE) up to 2.65 A W⁻¹ and 506%  are successfully applied to the VLC demonstration. This work provides a potential approach for the design and fabrication of optoelectronic devices with the requirement of high responsivity and photoelectric conversion efficiency.

A novel strategy for reducing the lateral size of Metal–Organic Layers (MOLs) is developed through a time-resolved solvothermal synthesis method that utilizes formic acid (FA) to regulate the acidity of the system, enabling rapid nucleation and controlled growth of the MOLs.

Abstract

Metal–Organic Layers (MOLs), 2D analogs of Metal–Organic Frameworks (MOFs), feature monolayer structures with the potential for various applications. Controlling the lateral size of MOLs is essential for enhancing their dispersibility in solvents and optimizing performance. However, reducing lateral dimensions while preserving monolayer thickness presents a challenge due to the precise conditions required for monolayer formation. This study utilizes a time-resolved solvothermal synthesis method, employing flow chemistry to adjust reaction conditions dynamically during different stages of MOL growth. Fast nucleation is triggered initially to generate numerous nuclei, followed by a shift to slower growth rates, limiting further expansion and preventing the formation of amorphous structures. This approach effectively refines the lateral dimensions of nano-MOLs while maintaining monolayer integrity. The reduction in lateral dimensions has a direct effect on improving catalytic performance, demonstrating the potential for fine-tuned nanosized MOLs in advanced applications.

Nature, Published online: 17 February 2025; doi:10.1038/s41586-025-08755-z

Highlights

• A soft, untethered electronic robot that integrates magnetically responsive engineered composites, enabling reversible programming and a diverse range of motions and shapes.

• Seamless integration of a meticulously designed soft/flexible electronic system with the magnetic soft robot guarantees the stable and accurate execution of multi-modal electrical functions while preserving the integrity of its mechanical movement.

• The comprehensive demonstration illustrates the feasibility of the untethered, integrated magnetic soft robot, highlighting its stable operation, adaptability, and ability to perform complex tasks under diverse conditions.

Hydrogen-associated topotactic transition toward a new robust hydrogenated phase is uncovered in metastable VO₂ via introducing non-equilibrium conditions. Establishing correlated VO₂ at metastable status extensively broadens the adjustability in electronic orbital configuration, enabling the rational design of exotic electronic states, but also elevates the driving force of the proton evolution for extensively tuning the energy landscape of electron-correlated system.

Abstract

The discovery of hydrogen-associated topotactic phase modulations in correlated oxide system has emerged as a promising paradigm to explore exotic electronic states and physical functionality. Here hydrogen-induced Mott phase transitions are demonstrated for metastable VO₂ (B) toward new electron-itinerant hydrogenated phases via introducing non-equilibrium condition, delicately delivering a rich spectrum of hydrogen-associated electronic states. Of particular interest, the highly robust but reversible hydrogenated phase achievable in metastable VO₂ (B) significantly benefits protonic device applications, which is in contrast with well-known VO₂ (M1), where the metallic hydrogenated phase readily turns into insulating state with extensive hydrogen doping. Establishing correlated VO₂ at metastable status fundamentally surpasses the thermodynamic restrictions to expand the adjustability in their electronic structure, giving rise to new electronic states and a superior resistive switching of 10²–10⁵ to the counterparts in widely-reported VO₂ (M1). Utilizing the theoretical calculations and synchrotron radiation analysis, the hydrogen-associated phase modulation in metastable VO₂ (B) is dominantly driven by band-filling-controlled orbital reconfiguration, while the concurrent structural evolution unveils a strong ion-electron-lattice coupling. The present work provides fundamentally new tuning knob for adjusting the energy landscape of electron-correlated system, advancing the rational design of unachievable electronic states in hydrogen-related equilibrium phase diagram.

Schematic depicting topics of multifaceted applications of gallium liquid metal: a wide range of explorations from fundamental property research to innovative applications such as photodetectors and neuromorphic systems.

Abstract

Gallium (Ga) liquid metal has become highly suitable for the preparation of 2D materials due to its unique physical and chemical properties, such as high surface tension, low-melting-point, and ease of oxidization. Ga has a very low melting point and becomes a silver-white liquid at 29.76 °C. In the air, the surface of Ga can spontaneously undergo a Cabrera-Mott oxidation reaction to form an ultra-thin oxide layer. This self-formed oxide layer is considered a natural 2D material, and other 2D materials can be derived by post-processing the oxide layer. In recent years, advancements in surface oxidation techniques for Ga have led to the successful preparation of various Ga-based 2D materials. These materials possess unique electronic and optical properties along with a simple, low-cost preparation process, offering broad potential for advancing new electronic devices. This review examines recent research on the preparation of Ga-based 2D materials derived from Ga and its alloys. It discusses the potential applications of different kinds of Ga-based 2D devices across multiple fields. Therefore, it can be expected that Ga will play a more significant role in the development of material science in the future.

This work demonstrates a strategy for depositing VO _x using thermal atomic layer deposition (ALD) followed by thermal annealing to synthesize VO₂. The thin film and core/shell wire memristors exhibit excellent switching performance and are highly sensitive to ambient temperature. This ALD approach to preparing key memristor materials paves the way for future high-density hardware neural networks.

Vanadium dioxide (VO₂) is a well-known candidate for memristor applications due to its insulator-to-metal transition (IMT) characteristics. The fabrication of memristor devices requires highly controlled synthesis processes concerning the material chemistry and geometry. Atomic layer deposition (ALD) offers unique advantages for the fabrication of hardware neural networks, such as miniaturization, conformality, and sub-nm thickness control. Herein, an ALD process for non-stoichiometric vanadium oxide (VO _x ) using tetrakis(dimethylamino)vanadium (TDMAV) and water as precursors is presented. Subsequently, a tailor-made annealing process converts VO _x into VO₂, which exhibits an IMT of about three orders of magnitude at around 70 °C, rendering it a promising memristor material. VO₂ thin film and Si–Al₂O₃/VO₂ core/shell memristors are fabricated and analyzed, both of which exhibited I–V hysteresis loops, indicating their suitability for memristor applications in both 2D and 3D morphologies. Additionally, these memristors are sensitive to the operation temperature, with the hysteresis loops narrowing and shifting toward lower voltages as temperature increases, eventually disappearing beyond VO₂'s intrinsic phase transition temperature. This study highlights the viability of ALD-assisted VO₂ for memristor applications and demonstrates its potential for advancing the three-dimensionalization of neuromorphic chips.