Jiuxiang Dai

Miniature robots have great prospects to transform targeted drug delivery. Here, a miniature soft robot is proposed, which can dispense four types of drugs with reprogrammable drug-dispensing sequence and dosage. This soft robot can inspire unprecedented, targeted combination therapy, where multiple drugs must be delivered to various disease sites, each with a specific sequence and dosage of drugs.

Abstract

Miniature robots are untethered actuators, which have great prospects to transform targeted drug delivery because they can potentially deliver high concentrations of medicine to the disease site(s) with minimal complications. However, existing miniature robots cannot perform advanced targeted combination therapy; majority of them can at most transport one type of drug, while those that can carry multiple drugs are unable to change their drug-dispensing sequence and dosage. Furthermore, the latter robots cannot transport more than three types of drugs, selectively dispense their drugs, maintain their mobility, or release their drugs at multiple sites. Here, a millimeter-scale soft robot is proposed, which can be actuated by alternating magnetic fields to dispense four types of drugs with reprogrammable drug-dispensing sequence and dosage (dispensing rates: 0.0992–0.231 µL h⁻¹). This robot has six degrees-of-freedom motions, and it can deliver its drugs to multiple desired sites by rolling and two-anchor crawling across unstructured environments with negligible drug leakage. Such dexterity is highly desirable and unprecedented for miniature robots with drug-dispensing capabilities. The soft robot therefore has great potential to enable advanced targeted combination therapy, where four types of drugs must be delivered to various disease sites, each with a specific sequence and dosage of drugs.

Achieving controllable oxidation of single-crystal Bi₂O₂Se through the development of large-scale UV-assisted intercalative oxidation allowed for the construction of β-Bi₂SeO₅/Bi₂O₂Se heterostructures. The β-Bi₂SeO₅/Bi₂O₂Se memristor exhibited remarkable self-rectifying memristive performance, including ultra-high ON/OFF and rectification ratios, and nonlinearity. The scalable production of self-rectifying memristor arrays is successfully demonstrated, showcasing sub-pA sneak currents, desirable to minimize cross-talk effects in high-density memristor arrays.

Abstract

Smart memristors with innovative properties are crucial for the advancement of next-generation information storage and bioinspired neuromorphic computing. However, the presence of significant sneak currents in large-scale memristor arrays results in operational errors and heat accumulation, hindering their practical utility. This study successfully synthesizes a quasi-free-standing Bi₂O₂Se single-crystalline film and achieves layer-controlled oxidation by developing large-scale UV-assisted intercalative oxidation, resulting β-Bi₂SeO₅/Bi₂O₂Se heterostructures. The resulting β-Bi₂SeO₅/Bi₂O₂Se memristor demonstrates remarkable self-rectifying resistive switching performance (over 10⁵ for ON/OFF and rectification ratios, as well as nonlinearity) in both nanoscale (through conductive atomic force microscopy) and microscale (through memristor array) regimes. Furthermore, the potential for scalable production of self-rectifying β-Bi₂SeO₅/Bi₂O₂Se memristor, achieving sub-pA sneak currents to minimize cross-talk effects in high-density memristor arrays is demonstrated. The memristors also exhibit ultrafast resistive switching (sub-100 ns) and low power consumption (1.2 pJ) as characterized by pulse-mode testing. The findings suggest a synergetic effect of interfacial Schottky barriers and oxygen vacancy migration as the self-rectifying switching mechanism, elucidated through controllable β-Bi₂SeO₅ thickness modulation and theoretical ab initio calculations.

This perspective article insights the fundamental of pyroelectricity in 2D materials that exhibits giant pyroelectric responses. It is spotlighting the potential merits to envision the scope of effective transient waste thermal energy harvesting, IR imaging, photodetectors, temperature sensors, bio-medical therapeutics, wastewater treatment, green hydrogen production and CO₂ reduction.

Abstract

Polar 2D materials hold the emerging functionalities such as ferro-, piezo-, and pyro-electric properties. On account of infrared-active low bandgap and polar nature at reduced dimensionality, they served as an ideal choice of pyroelectric material. It can cover up a diverse range of applications, such as waste thermal energy harvesting, IR imaging, photodetector, temperature sensors, and several catalytic processes due to the abundance of dynamic thermal fluxes. Recently, 2D pyroelectric materials have manifested a substantial role in thermal energy harvesting. Consequently, it is realized that there are plenty of scopes available to diversify its applicability. Thus, the challenges are spotlighted in this perspective to envision the desired 2D pyroelectric materials to achieve the effective thermal energy harvesting, sensing, and catalytic efficacy. Particularly, the emphasis is given to elucidate the role of spontaneous polarization in 2D materials to ascertain the giant pyroelectricity.

The growth via chemical vapor deposition of decoupled graphene on crystalline Cu(111) films deposited on sapphire is introduced. The resulting graphene is lying atop a thin Cu₂O layer and is charge neutral, low strained, and easy to transfer. Electrical transport measurements reveal excellent room temperature carrier mobilities, exceeding 10⁵ cm² V⁻¹ s⁻¹ upon encapsulation in hexagonal boron nitride, thus opening realistic pathways for high-performance next-generation applications.

Abstract

The growth of high-quality graphene on flat and rigid templates, such as metal thin films on insulating wafers, is regarded as a key enabler for technologies based on 2D materials. In this work, the growth of decoupled graphene is introduced via non-reducing low-pressure chemical vapor deposition (LPCVD) on crystalline Cu(111) films deposited on sapphire. The resulting film is atomically flat, with no detectable cracks or ripples, and lies atop of a thin Cu₂O layer, as confirmed by microscopy, diffraction, and spectroscopy analyses. Post-growth treatment of the partially decoupled graphene enables full and uniform oxidation of the interface, greatly simplifying subsequent transfer processes, particularly dry-pick up — a task that proves challenging when dealing with graphene directly synthesized on metallic Cu(111). Electrical transport measurements reveal high carrier mobility at room temperature, exceeding 10⁴ cm² V⁻¹ s⁻¹ on SiO₂/Si and 10⁵ cm² V⁻¹ s⁻¹ upon encapsulation in hexagonal boron nitride (hBN). The demonstrated growth approach yields exceptional material quality, in line with micro-mechanically exfoliated graphene flakes, and thus paves the way toward large-scale production of pristine graphene suitable for high-performance next-generation applications.

A range of inkjet-printable 2D material inks is prepared for the fabrication of inkjet-printed, ultra-flexible and machine-washable 2D material heterostructure-based textile micro-supercapacitors. Such micro-supercapacitors demonstrate higher energy (≈18.06 µWh cm^‒2) and power densities (≈4333.33 µW cm^‒2), as well as ≈82.48% higher areal capacitance with excellent capacitance retention (≈95% after 1000 cycles).

Abstract

Wearable electronic textiles (e-textiles) have emerged as promising healthcare solutions, offering point-of-care diagnostics while maintaining breathability, comfort, durability, and environmental stability with strong mechanical performance. However, the lack of thin and flexible power supplies hinders their practical adoption. In this regard, textile-based micro-energy storage devices present an appealing solution. Inkjet printing offers the capability to produce high-quality prints with sharp details and versatile substrate compatibility, making it an ideal choice for a wide array of printing applications. Here, the preparation of a range of inkjet-printable 2D material inks is reported for the fabrication of ultra-flexible and machine-washable textile micro-supercapacitors. Then 2D material heterostructures are proposed to enhance the performance of textile supercapacitors. This study reveals that a unique combination of highly conductive graphene with an insulator hexagonal boron nitride (h-BN) can enhance the areal capacitance of graphene-based textile supercapacitors by ≈82.48%. The heterostructure-based supercapacitors also demonstrate higher energy (≈18.06 µWh cm⁻²) and power densities (≈4333.33 µW cm⁻²) with excellent capacitance retention (≈95% after 1000 cycles). These findings on inkjet-printed heterostructure-based supercapacitors may herald a new era for the future application of high-performance micro-supercapacitors within textile-based wearable technology.

Nature Materials, Published online: 10 September 2024; doi:10.1038/s41563-024-01993-y

Second-order superlattices emerging in magic-angle twisted bilayer graphene aligned with hexagonal boron nitride are visualized in real space through cryogenic nano-imaging, revealing the impact of strain and twist-angle variations.

The magnetically torque-driven all-terrain microrobot (MTMR) designed in this study demonstrates exceptional mobility over various complex terrains. The microrobot also features precise cargo manipulation capabilities, making it potentially valuable for medical applications such as thrombus removal and minimally invasive hemostasis in cases of internal bleeding. This capability offers advanced solutions for minimally invasive surgery in complex environments.

Abstract

All-terrain microrobots possess significant potential in modern medical applications due to their superior maneuverability in complex terrains and confined spaces. However, conventional microrobots often struggle with adaptability and operational difficulties in variable environments. This study introduces a magnetic torque-driven all-terrain multiped microrobot (MTMR) to address these challenges. By coupling the structure's multiple symmetries with different uniform magnetic fields, such as rotating and oscillating fields, the MTMR demonstrates various locomotion modes, including rolling, tumbling, walking, jumping, and their combinations. Experimental results indicate that the robot can navigate diverse terrains, including flat surfaces, steep slopes (up to 75°), and gaps over twice its body height. Additionally, the MTMR performs well in confined spaces, capable of passing through slits (0.1 body length) and low tunnels (0.25 body length). The robot shows potential for clinical applications like minimally invasive hemostasis in internal bleeding and thrombus removal from blood vessels through accurate cargo manipulation capability. Moreover, the MTMR can carry temperature sensors to monitor environmental temperature changes in real time while simultaneously manipulating objects, displaying its potential for in-situ sensing and parallel task implementation. This all-terrain microrobot technology demonstrates notable adaptability and versatility, providing a solid foundation for practical applications in interventional medicine.

npj 2D Materials and Applications, Published online: 11 September 2024; doi:10.1038/s41699-024-00495-4

Metastable square Bismuth allotrope oriented by six-fold symmetric mica

Nature, Published online: 11 September 2024; doi:10.1038/s41586-024-07925-9

A molecular aggregate formed in a two-dimensional organic–inorganic hybrid perovskite superlattice with a near-equilibrium distance is shown to have a near-unity photoluminescence quantum yield like that of single molecules, despite being in an aggregated state.

Nature, Published online: 11 September 2024; doi:10.1038/s41586-024-07792-4

The charge carrier polarity and concentrations in an emissive perovskite semiconductor can be adjusted by incorporating a molecular dopant widely used for the passivation and structural control of optoelectronic perovskite materials.

Nature, Published online: 11 September 2024; doi:10.1038/d41586-024-02659-0

A family of semiconductors known as perovskites has great promise for use in optoelectronic devices. A much-needed strategy for adjusting the density of charge carriers in these materials unleashes their potential.

Atomic force microscopy reveals the elusive structure of the aluminum oxide surface

Iron oxychloride (FeOCl) is introduced as a novel cocatalyst simply grafted on BiVO₄ to construct an integrated photoanode, enhancing PEC performance. The formation of FeOCl/BiVO₄ heterojunction can simultaneously promote the transfer of photogenerated electrons, and improve the separation efficiency and light absorption efficiency.

Abstract

Bismuth vanadate (BiVO₄), as a promising photoanode for photoelectrochemical (PEC) water splitting, suffers from poor charge separation efficiency and light absorption efficiency. Herein, iron oxychloride (FeOCl) is introduced as a novel cocatalyst simply grafted on BiVO₄ to construct an integrated photoanode, enhancing PEC performance. The optimized FeOCl/BiVO₄ photoanode exhibits a superior photocurrent density value of 5.23 mA cm⁻² at 1.23 V versus reversible hydrogen electrode (RHE) under AM 1.5G illuminations. From experimental analysis, such high PEC performance is ascribed to the unique properties of FeOCl, facilitating charge transport, increasing light absorption efficiency, and promoting water oxidation kinetics. Density functional theory calculations further confirm that FeOCl optimizes the Gibbs free energy of H and O-containing intermediates (OOH^*) during PEC processes, boosting the catalytic kinetics of PEC water splitting. This work presents FeOCl as a promising catalyst for constructing high efficient PEC water-splitting photoanodes.

This work demonstrates the odd-even layer-dependence of out-of-plane ferroelectricity in ε-InSe. The device based on the ε-InSe achieves an on/off ratio of 10⁴ in ferroelectric tunneling junction and ultrafast bulk photovoltaic response in photodetector in the near-infrared band. Moreover, the photoresponse in ε-InSe can even exceed graphene in the same conditions, confirming the possibility of application in multifunctional devices.

Abstract

2D sliding ferroelectric semiconductors have greatly expanded the ferroelectrics family with the flexibility of bandgap and material properties, which hold great promise for ultrathin device applications that combine ferroelectrics with optoelectronics. Besides the induced different resistance states for non-volatile memories, the switchable ferroelectric polarizations can also modulate the photogenerated carriers for potentially ultrafast optoelectronic devices. Here, it is demonstrated that the room temperature sliding ferroelectricity can be used for ultrafast switchable photovoltaic response in ε-InSe layers. By first-principles calculations and experimental characterizations, it is revealed that the ferroelectricity with out-of-plane (OOP) polarization only exists in even layer ε-InSe. The ferroelectricity is also demonstrated in ε-InSe-based vertical devices, which exhibit high on-off ratios (≈10⁴) and non-volatile storage capabilities. Moreover, the OOP ferroelectricity enables an ultrafast (≈3 ps) bulk photovoltaic response in the near-infrared band, rendering it a promising material for self-powered reconfigurable and ultrafast photodetector. This work reveals the essential role of ferroelectric polarization on the photogenerated carrier dynamics and paves the way for hybrid multifunctional ferroelectric and optoelectronic devices.

The defect reduction efficiency via a facile “growth-repair” strategy for MoS₂ wafers is quantitatively investigated. A low sulfur defect density of 4.28 × 10¹² cm⁻² is achieved, which is caused by dramatic increase of defect formation energy neighboring substitutional oxygen atoms. The repaired MoS₂ shows enhanced electrical and optical properties, paving the way toward future electronic and optoelectronic devices.

Abstract

Atomic chalcogen vacancy is the most commonly observed defect category in two dimensional (2D) transition-metal dichalcogenides, which can be detrimental to the intrinsic properties and device performance. Here a low-defect density, high-uniform, wafer-scale single crystal epitaxial technology by in situ oxygen-incorporated “growth-repair” strategy is reported. For the first time, the oxygen-repairing efficiency on MoS₂ monolayers at atomic scale is quantitatively evaluated. The sulfur defect density is greatly reduced from (2.71 ± 0.65) × 10¹³ down to (4.28 ± 0.27) × 10¹² cm⁻², which is one order of magnitude lower than reported as-grown MoS₂. Such prominent defect deduction is owing to the kinetically more favorable configuration of oxygen substitution and an increase in sulfur vacancy formation energy around oxygen-incorporated sites by the first-principle calculations. Furthermore, the sulfur vacancies induced donor defect states is largely eliminated confirmed by quenched defect-related emission. The devices exhibit improved carrier mobility by more than three times up to 65.2 cm² V⁻¹ s⁻¹ and lower Schottky barrier height reduced by half (less than 20 meV), originating from the suppressed Fermi-level pinning effect from disorder-induced gap state. The work provides an effective route toward engineering the intrinsic defect density and electronic states through modulating synthesis kinetics of 2D materials.

A novel supramolecular scaffold with precisely positioned structure-forming and functional units (electrical dipoles and magnetic spins) is designed so that self-assembly results in functional unit organization. The xerogel derived from this organogel exhibits the highest magnetoelectric coupling coefficient (α_ME ≈ 216 mV Oe⁻¹ cm⁻¹) reported to date for organic materials. This organic multiferroic material efficiently captures and utilizes stray magnetic fields for sustainable energy harvesting.

Abstract

Magnetoelectric materials are highly desirable for technological applications due to their ability to produce electricity under a magnetic field. Among the various types of magnetoelectric materials studied, their organic counterparts provide an opportunity to develop solution-processable, flexible, lightweight, and wearable electronic devices. However, there is a rare choice of solution-processable, flexible, lightweight magnetoelectric materials which has tremendous technological interest. A supramolecular scaffold with precisely positioned structure-forming and functional units (electrical dipoles and magnetic spins) is designed so that self-assembly results in functional unit organization. Structure-forming segments allow these scaffolds to self-assemble into hierarchically ordered structures in nonpolar solvents, creating nanofibrous organogel networks. In particular, the xerogel derived from this organogel exhibits the highest magnetoelectric coupling coefficient (α_ME ≈ 216 mV Oe⁻¹ cm⁻¹) reported to date for organic materials. This is even greater than commonly envisioned composite materials made of piezoelectric polymers and inorganic magnets. This single-component organic multiferroic material displays ferroelectricity (T_c ≈ 46 °C) and paramagnetic behavior at room temperature. With this, it is demonstrated that the possibilities of effectively harvesting stray magnetic fields that are copiously available in the surroundings and wasted otherwise.

Herein, a fast and convenient laser patterning method for preparing patterned 2D lateral/vertical metal/semiconducting VS₂/MoS₂ (VSe₂/WSe₂) heterostructures is developed. The obtained patterned vertical van Waals heterostructures (vdWHs) show a similar channel length of ≈420  nm and high-quality contact interfaces. Based on the patterned vdWHs, vdW-contacted MoS₂ (WSe₂) transistors with relatively high performance can be readily fabricated.

Abstract

2D metal/semiconducting heterostructures have attracted extensive attention for potential applications in future electronic and optoelectronic devices. However, the simple and fast preparation of patterned metal/semiconducting heterostructures with controllable channel lengths still faces challenges. Here, a simple and reliable laser patterning method for preparing patterned lateral/vertical 1T/2H VS₂/MoS₂ metal/semiconducting heterostructures is reported. Specifically, site-selective etching of VS₂ can be realized through the combination of laser radiation and acid solution etching. Further, pre-patterned VS₂ nanoplates with edge dangling bonds can offer effective nucleation points for the lateral epitaxial growth of MoS₂, thus generating patterned VS₂-MoS₂ lateral heterostructures. The laser processing method can further be used to create patterned VS₂/MoS₂ vertical van der Waals (vdWHs), which can only selectively etch the upper layer VS₂ while maintaining the intrinsic structure of the bottom layer MoS₂. The obtained patterned VS₂/MoS₂ vdWHs show a similar channel length of ≈420 nm, and the VS₂ vdW contact MoS₂ transistor is fabricated, delivering an On-state current of 4.01 µA/µm, and carrier mobility of 3.56 cm² s⁻¹ V⁻¹. This approach is also general for preparing patterned VSe₂, VSe₂/WSe₂ heterostructures.

2D magnetic materials with high spin polarization and Curie temperature are ideal for ultrathin spintronic devices. This study, integrating first-principles calculations with machine learning methods, demonstrates that Cr₂CO _x MXene consistently exhibits high spin polarization and elevated Curie temperatures across various O adsorption configurations. These findings highlight Cr₂CO _x MXene as a promising candidate for advanced ultrathin spintronic applications.

Abstract

2D magnetic materials with high spin polarization and Curie temperature are highly desirable for ultrathin spintronic devices. This study utilizes first-principles methods to systematically investigate 225 O adsorption configurations, demonstrating that Cr₂CO _x MXene consistently maintains a long-range-ordered ferromagnetic arrangement with high spin polarization, irrespective of the O adsorption configuration. Most configurations also display Curie temperature (T _C) exceeding room temperature, with the possibility of further enhancement by reducing O coverage. Machine learning models are developed to accurately predict O adsorption configurations, exchange interaction energies, and T _C. A novel approach of stripping F and OH groups to create Cr₂CO _x on Cr-based MXene surfaces is proposed to address the difficulty in achieving long-range-ordered magnetic structures by manipulating surface adsorbates in MXene. This approach enhances the ability to control the magnetic properties of MXenes and paves the way for their application in ultrathin spintronic devices.

The formation process of nano-patterned biologically-formed silica is investigated using in situ electron microscopy that allows for 3D visualization at the nanometer scale. The data show a two-step process that yields a hexagonal lattice based on the sequential formation of parallel rods, followed by their connection via evenly spaced bridges.

Abstract

Organisms are able to control material patterning down to the nanometer scale. This is exemplified by the intricate geometrical patterns of the silica cell wall of diatoms, a group of unicellular algae. Theoretical and modeling studies propose putative physical and chemical mechanisms to explain morphogenesis of diatom silica. Nevertheless, direct investigations of the underlying formation process are challenging because this process occurs within the confines of the living cell. Here, a method is developed for in situ 3D visualization of silica development in the diatom Stephanopyxis turris, using electron microscopy slice-and-view techniques. The formation of an isotropic hexagonal pattern made of nanoscale pores is documented. Surprisingly, these data reveal a directional process that starts with elongation of silica rods along one of the three equivalent orientations of the hexagonal lattice. Only as a secondary step, these rods are connected by crisscrossing bridges that give rise to the complete hexagonal pattern. These in situ observations combine two known properties of diatom silica, close packing of pores and branching of rods, to a unified process that yields isotropic patterns from an anisotropic background. Future research into diatom morphogenesis should focus on rod elongation and branching as the key for pattern formation.

A novel type of spatially indirect exciton in two-dimensional Bi₂S₂Te monolayer due to its unique structure is identified. The spin-singlet excitons are dipole/parity allowed and feature with small effective mass and large binding energy. High-temperature excitonic Bose–Einstein condensation and superfluidity can be anticipated, offering a fascinating platform for exploring excitonic condensation and the development of excitonic dissipationless nanodevices.

Abstract

Exploration of high-temperature bosonic condensation is of significant importance for the fundamental many-body physics and applications in nanodevices, which, however, remains a huge challenge. Here, in combination of many-body perturbation theory and first-principles calculations, a new-type spatially indirect exciton can be optically generated in two-dimensional (2D) Bi₂S₂Te because of its unique structure feature. In particular, the spin-singlet spatially indirect excitons in Bi₂S₂Te monolayer are dipole/parity allowed and reveal befitting characteristics for excitonic condensation, such as small effective mass and satisfied dilute limitation. Based on the layered Bi₂S₂Te, the possibility of the high-temperature excitonic Bose–Einstein condensation (BEC) and superfluid state in two dimensions, which goes beyond the current paradigms in both experiment and theory, are proved. It should be highlighted that record-high phase transition temperatures of 289.7 and 72.4 K can be theoretically predicted for the excitonic BEC and superfluidity in the atomic thin Bi₂S₂Te, respectively. It therefore can be confirmed that Bi₂S₂Te featuring bound bosonic states is a fascinating 2D platform for exploring the high-temperature excitonic condensation and applications in such as quantum computing and dissipationless nanodevices.