Jing Zhang

Nature, Published online: 18 November 2022; doi:10.1038/d41586-022-03603-w

Soft robot that snaps its ‘wings’ overcomes the inefficiency of earlier swimming devices.

Surface charge plays key roles in regulating ionic transport within 2D nanofluidic membranes toward various applications involving energy and environment. This review introduces the surface charge modification principles and strategies of 2D nanofluidic membranes for the first time, which are of great significance for improving the ion regulation capability of membranes and realizing material design based on biomimetic nanochannels.

Abstract

2D nanofluidic membranes are capable of regulating ion transport toward various applications concerning energy and environment, which is primarily contributed by the excess charge on the interior surface of narrow nanoscale pores. However, there is still a lack of comprehensive summaries and discussions on the surface charge modification principles and strategies of 2D nanofluidic membranes, as well as the practical applications of charge-modified 2D nanofluidic membranes for regulating ion transport. In this review, the surface charge modification principles and charge modification methods of 2D nanofluidic membranes are first introduced in detail, which is of great significance for improving the ion regulation capability of membranes and realizing the design of nanochannel materials. Next, recent advances in the two typical applications of concentration cells and water treatment based on charge-modified 2D nanofluidic membranes are summarized. Finally, some challenges and prospects related to charge-modified 2D nanofluidic membranes are discussed to indicate directions for future research in this field. It is anticipated that this review will provide valuable strategies for the development of high-performance charge-modified 2D nanofluidic membranes toward energy and environment applications.

A new type of second near-infrared (NIR-II) (1532 nm) light responsive upconversion nanoparticles with enhanced single-band red upconversion emission and controllable phase and size is designed by introducing Er³⁺ as sensitizer and utilizing Mn²⁺ as energy manipulator. Moreover, NIR-II light activated red upconversion bioimaging and photodynamic therapy are successfully achieved for the first time.

Abstract

Lanthanide based upconversion (UC) nanoprobes have emerged as promising agents for biological applications. Extending the excitation light to the second near-infrared (NIR-II), instead of the traditional 980/808 nm light, and realizing NIR-II responsive single-band red UC emission is highly demanded for bioimaging application, which has not yet been explored. Here, a new type of NIR-II (1532 nm) light responsive UC nanoparticles (UCNPs) with enhanced single-band red UC emission and controllable phase and size is designed by introducing Er³⁺ as sensitizer and utilizing Mn²⁺ as energy manipulator. Through tuning the content of Mn²⁺ in NaLnF₄:Er/Mn, the crystal phase, size, and emitting color are readily controlled, and the red-to-green (R/G) ratio is significantly increased from ≈20 to ≈300, leading to NIR-II responsive single band red emission via efficient energy transfer between Er³⁺ and Mn²⁺. In addition, the single band red emitting intensity can be further improved by coating shell to avoid the surface quenching effect. More importantly, NIR-II light activated red UC bioimaging and photodynamic therapy through loading photosensitizer of zinc phthalocyanine are successfully achieved for the first time. These findings provide a new strategy of designing NIR-II light responsive single-band red emissive UCNPs for biomedical applications.

Highly crystalline single layer 2D polymers (SL-2DPs) are prepared and further used as an active layer in the memristor. The devices exhibit low variability, high reliability in terms of yield, stability and durability, nanometer scalability, as well as distinguished bending endurance, which verified the unambiguous role of SL-2DP film in diverse applications from high density information storage to ultra-thin flexible electronics.

Abstract

Large-scale growth of highly crystalline single layer 2D polymers (SL-2DPs) and their subsequent integration into memristors is key to advancing the development of high-density data storage devices. However, leakage problems resulting from the porous structure of 2DPs continue to make such advances extremely challenging. Herein, we overcome this issue by incorporating long alkoxy chains into key molecular building blocks to obtain a highly crystalline 2DP, as visualized by scanning tunneling microscopy, and prevent metal permeation in the subsequent device fabrication process. SL-2DP memristors constructed via direct evaporation of the top electrodes exhibit low variability (σ_Vset = 0.14) due to the single-monomer-thick feature together with the high regular structure and coordination ability which minimizes the stochastic spatial distribution of conductive filaments (CFs) in both vertical and lateral dimensions. The variability is further decreased to 0.04 by confining the formation and fracture of CFs to the interface through the utilization of bilayer junctions. Using peak force tunneling atomic force microscopy, the nanometer scalability (< 50 nm²) and low power consumption of these molecular memristor devices are demonstrated.

Chemical synthesis and functionalization of 2D germananes (hydrogen atom and covalent group(s) termination) via topotactical deintercalation offer customizable properties or new functionalities. The fundamentals from synthesis and exfoliation to properties; for optoelectronics, catalysis, energy conversion and storage, sensors, and biomedical applications are reviewed. The review presents the recent progress and challenges, and provides insight for future exploration of these materials.

Abstract

In the realm of 2D layered materials, the monoelemental group 14 Xene, germanene, as the germanium analog of graphene, has emerged as the next prospective candidate. Preceded by silicon, germanium is widely used in the semiconductor industry; thus, germanene is deemed compatible with existing semiconductor technologies. Germanene consists of mixed sp²–sp³-hybridized networks in a buckled hexagonal honeycomb structure. Chemical exfoliation of Zintl phases, such as CaGe₂, specifically the topotactical deintercalation in acidic media, removes the alkaline earth metal ions Ca²⁺, giving rise to layered germanane (germanene with the Ge centers covalently saturated with terminal hydrogen atoms). Diverse variants of functionalized germananes (with covalent group(s) termination) can be obtained by varying the topotactical deintercalation precursors, elevating the game with limitless functionalization possibilities for customizable properties or new functionalities. The preparation of Zintl phases to the details of functionalized and modified germananes and their properties, and the additional exfoliation step to achieve mono- or few-layer germananes, are comprehensively covered. The progress and challenges of 2D functionalized germananes in optoelectronics, catalysis, energy conversion and storage, sensors, and biomedical areas are reviewed. This review provides insight into designing and exploring this class of atomically thin semiconductors in realizing future nanoarchitectonics.

Post-synthesis doping of InAs nanocrystals with Zn enables the fabrication of heavy metal free, RoHS compliant nanocrystal-based field effect transistors, which exhibit either n- or p-type characteristics. Advanced structural characterization of the doped nanocrystals highlights the importance of Zn dopant chemistry on the doping efficiency. This study sets the stage for future development of nanocrystals-based opto-electronics applications.

Abstract

Doped heavy metal-free III–V semiconductor nanocrystal quantum dots (QDs) are of great interest both from the fundamental aspects of doping in highly confined structures, and from the applicative side of utilizing such building blocks in the fabrication of p–n homojunction devices. InAs nanocrystals (NCs), that are of particular relevance for short-wave IR detection and emission applications, manifest heavy n-type character poising a challenge for their transition to p-type behavior. The p-type doping of InAs NCs is presented with Zn – enabling control over the charge carrier type in InAs QDs field effect transistors. The post-synthesis doping reaction mechanism is studied for Zn precursors with varying reactivity. Successful p-type doping is achieved by the more reactive precursor, diethylzinc. Substitutional doping by Zn²⁺ replacing In³⁺ is established by X-ray absorption spectroscopy analysis. Furthermore, enhanced near infrared photoluminescence is observed due to surface passivation by Zn as indicated from elemental mapping utilizing high-resolution electron microscopy corroborated by X-ray photoelectron spectroscopy study. The demonstrated ability to control the carrier type, along with the improved emission characteristics, paves the way towards fabrication of optoelectronic devices active in the short-wave infrared region utilizing heavy-metal free nanocrystal building blocks.

In this work, a facile strategy base on bifunctional zwitterions is proposed that effectively modulates the crystallization kinetics of quantum wells—both suppressing the formation of low-n phases and restricting the growth of high-n phases—contributing to a narrow n distribution. Accordingly, high-performance sky-blue PeLEDs at 490 nm with a recorded EQE of 15.6% are realized.

Abstract

While quasi-two-dimensional (quasi-2D) perovskites have emerged as promising semiconductors for light-emitting diodes (LEDs), the broad-width distribution of quantum wells hinders their efficient energy transfer and electroluminescence performance in blue emission. In particular, the underlying mechanism is closely related to the crystallization kinetics and has yet to be understood. Here for the first time, the influence of bifunctional zwitterions with different coordination affinity on the crystallization kinetics of quasi-2D perovskites is systematically investigated. The zwitterions can coordinate with Pb²⁺ and also act as co-spacer organic species in quasi-2D perovskites, which collectively inhibit the aggregation of colloidal precursors and shorten the distance of quantum wells. Consequently, restricted nucleation of high-n phases and promoted growth of low-n phases are achieved with moderately coordinated zwitterions, leading to the final film with a more concentrated n distribution and improved energy transfer efficiency. It thus enables high-efficiency blue LEDs with a recorded external quantum efficiency of 15.6% at 490 nm, and the operation stability has also been prolonged to 55.3 min. These results provide useful directions for tuning the crystallization kinetics of quasi-2D perovskites, which is expected to lead to high-performance perovskite LEDs.

Prototypical gate-programmable memory that seamlessly integrates the functionality of both ferroelectric memristor and metal-oxide-semiconductor field effect transistor (MOS-FET), in a vertical fashion is demonstrated. Its memristive characteristics can be quenched (enabled), by setting the Fermi level of MoS₂ inside (outside) of its band gap via a top gate, yielding a gate programmable non-volatile memory for multi-bit data storage and more.

Abstract

Ferroelectricity, one of the keys to realize non-volatile memories owing to the remanent electric polarization, is an emerging phenomenon in the 2D limit. Yet the demonstrations of van der Waals (vdW) memories using 2D ferroelectric materials as an ingredient are very limited. Especially, gate-tunable ferroelectric vdW memristive device, which holds promises in future multi-bit data storage applications, remains challenging. Here, a gate-programmable multi-state memory is shown by vertically assembling graphite, CuInP₂S₆, and MoS₂ layers into a metal(M)-ferroelectric(FE)-semiconductor(S) architecture. The resulted devices seamlessly integrate the functionality of both FE-memristor (with ON–OFF ratios exceeding 10⁵ and long-term retention) and metal-oxide-semiconductor field effect transistor (MOS-FET). Thus, it yields a prototype of gate tunable giant electroresistance with multi-levelled ON-states in the FE-memristor in the vertical vdW assembly. First-principles calculations further reveal that such behaviors originate from the specific band alignment between the FE-S interface. Our findings pave the way for the engineering of ferroelectricity-mediated memories in future implementations of 2D nanoelectronics.

Nature Communications, Published online: 17 November 2022; doi:10.1038/s41467-022-34690-y

Publisher Correction: Towards highly efficient NIR II response up-conversion phosphor enabled by long lifetimes of Er³⁺

Nature Materials, Published online: 17 November 2022; doi:10.1038/s41563-022-01398-9

Low-power and compact active pixel sensor (APS) matrices are desired for resource-limited edge devices. Here, the authors report a small-footprint APS matrix based on monolayer MoS2 phototransistors arrays exhibiting spectral uniformity, reconfigurable photoresponsivity and de-noising capabilities at low energy consumption.

Nature Materials, Published online: 17 November 2022; doi:10.1038/s41563-022-01401-3

The authors report a crossover from easy-plane to easy-axis magnetic anisotropy in monolayer RuCl3, which they attribute to an in-plane distortion of the Cl atoms observed in electron diffraction that modify the non-Kitaev exchange terms. The results are useful for overcoming the challenge of realizing a quantum spin liquid.

Nature Electronics, Published online: 17 November 2022; doi:10.1038/s41928-022-00858-z

A van der Waals heterostructure that has a partial floating-gate field-effect transistor device architecture can function as both reconfigurable transistor and reconfigurable non-volatile memory, and can provide reconfigurable logic-in-memory capabilities.

Lattice-matched InSb/CdTe heterostructures are utilized to tailor the nonreciprocal charge transport up to room temperature. Benefiting from both the inversion symmetry breaking and interfacial Rashba spin–orbit coupling, this nonmagnetic hybrid system not only warrants a pronounced unidirectional magnetoresistance effect, but also enables highly efficient gate tuning of the rectification response, hence offering feasible strategies for controllable spin–orbit applications.

Abstract

Symmetry manipulation can be used to effectively tailor the physical order in solid-state systems. With the breaking of both the inversion and time-reversal symmetries, nonreciprocal magneto-transport may arise in nonmagnetic systems to enrich spin–orbit effects. Here, the observation of unidirectional magnetoresistance (UMR) in lattice-matched InSb/CdTe films is investigated up to room temperature. Benefiting from the strong built-in electric field of 0.13 V nm⁻¹ in the heterojunction region, the resulting Rashba-type spin–orbit coupling and quantum confinement result in a distinct sinusoidal UMR signal with a nonreciprocal coefficient that is 1–2 orders of magnitude larger than most non-centrosymmetric materials at 298 K. Moreover, this heterostructure configuration enables highly efficient gate tuning of the rectification response, wherein the UMR amplitude is enhanced by 40%. The results of this study advocate the use of narrow-bandgap semiconductor-based hybrid systems with robust spin textures as suitable platforms for the pursuit of controllable chiral spin–orbit applications.

Nature Communications, Published online: 16 November 2022; doi:10.1038/s41467-022-34043-9

The Su-Schrieffer-Heeger (SSH) model is a prototypical model of topological states, initially proposed to describe spinless electrons on a one-dimensional (1D) dimerized lattice. Here, the authors realize a 2D SSH model in a rectangular lattice of silicon atoms on a silver substrate, observing gapped Dirac cones by angle-resolved photoemission spectroscopy.

Nature Communications, Published online: 17 November 2022; doi:10.1038/s41467-022-34774-9

The scalability of neuromorphic devices depends on the dismissal of capacitors and additional circuits. Here Liu et al. report an artificial neuron based on the polarization and depolarization of an anti-ferroelectric film, avoiding additional elements and reaching 37 fJ/spike of power consumption.

Nature Synthesis, Published online: 14 November 2022; doi:10.1038/s44160-022-00182-6

Mechanical cleavage of layered materials to obtain two-dimensional (2D) sheets is restricted to materials with interlayer interactions dominated by van der Waals (vdW) forces. Here, calendering is used to weaken interlayer binding in non-vdW layered structures (metals, semiconductors and superconductors) allowing mechanical exfoliation to obtain 2D sheets with thickness-dependent properties.

Nature Physics, Published online: 14 November 2022; doi:10.1038/s41567-022-01812-8

A form of superconductivity where strong spin–orbit coupling combines with topological band inversions to produce strong robustness against magnetic fields is shown in a few-layer transition metal dichalcogenide.

Nature Physics, Published online: 14 November 2022; doi:10.1038/s41567-022-01824-4

Superconductivity with an anisotropy is revealed in a layered material. This result points towards a version of superconductivity where spin–orbit interactions produce a material that is resilient to external magnetic fields.

MXene, an emerging 2D material, exhibits fascinating optoelectronic properties and is considered a promising contender for the new-generation in-memory and neuromorphic computing technology. This review systematically summarizes the recent progress of MXene-based memristors in data storage, artificial synapses, neuromorphic computing, and logic operation. The challenges and development perspectives are also discussed.

Abstract

Confronted by the difficulties of the von Neumann bottleneck and memory wall, traditional computing systems are gradually inadequate for satisfying the demands of future data-intensive computing applications. Recently, memristors have emerged as promising candidates for advanced in-memory and neuromorphic computing, which pave one way for breaking through the dilemma of current computing architecture. Till now, varieties of functional materials have been developed for constructing high-performance memristors. Herein, the review focuses on the emerging 2D MXene materials-based memristors. First, the mainstream synthetic strategies and characterization methods of MXenes are introduced. Second, the different types of MXene-based memristive materials and their widely adopted switching mechanisms are overviewed. Third, the recent progress of MXene-based memristors for data storage, artificial synapses, neuromorphic computing, and logic circuits is comprehensively summarized. Finally, the challenges, development trends, and perspectives are discussed, aiming to provide guidelines for the preparation of novel MXene-based memristors and more engaging information technology applications.

An Ti₃C₂T _x  (MXene)-encapsulated magnetic liquid metal (MX–MLM) is synthesized for application to 3D-motion-adaptive synapses. The MX–MLM exhibits magnetic-field-induced shape deformability, locomotion, self-healability, recyclability, and nonwettability and has excellent potential for application to single-neural-network artificial-intelligence-based magnetic-path-tracking systems to simultaneously sense, learn, and adapt to different magnetic fields.

Abstract

Owing to their unique surface chemistry, room-temperature pseudoliquidity, and high electrical conductivity, gallium-based liquid metals (LMs) exhibit multifunctionality. To grant deformable and self-flowing characteristics to LMs, magnetic particles are incorporated for precisely controlling the LM motion and shape deformability. However, LM surface-adhesion and corrosivity hinders the integration of LMs into complex circuits and devices owing to potential alloying with other metals and contamination of their surroundings. In this study, a highly conductive Ti₃C₂T _x (MXene)-encapsulated magnetic LM (MX–MLM) is developed using a feasible fabrication method. The MX–MLM comprises magnetic particles suspended within its core and self-assembled MXene flakes on the surface to maintain the nonwettability and high electrical conductivity of a liquid droplet. The noncorrosivity and increased magnetism of the MX–MLM enable nonstick magnetic-field-induced locomotion and shape deformation on various surfaces including metals, oxides, and polymers. Furthermore, the MX–MLM exhibits recyclability and magnetic-field-induced self-healing. To demonstrate its functionality, the MX–MLM is employed as a magnetointeractive, shape-deformable, and locomotive top gate electrode in a transistor fabricated using a ferroelectric polymer gate insulator. The device exhibits excellent magnetointeractive synaptic capability for detecting and learning 3D path information.

Nature Electronics, Published online: 14 November 2022; doi:10.1038/s41928-022-00891-y

Author Correction: Bilayer tungsten diselenide transistors with on-state currents exceeding 1.5 milliamperes per micrometre