Jing Zhang

Nature Communications, Published online: 29 November 2022; doi:10.1038/s41467-022-35226-0

Potential application of Titanium carbide MXene in wearable devices is limited by the formation of voids during assembly. Here, the authors demonstrate a synergistic densification strategy by intercalating small flakes and interfacial bridging to obtain high-performance MXene films.

Nature Materials, Published online: 28 November 2022; doi:10.1038/s41563-022-01407-x

An apparent quirk of mathematics draws on a symmetry and resolves the issue of how to determine the equilibrium shape of crystals of two-dimensional materials with asymmetric terminations.

Nature, Published online: 28 November 2022; doi:10.1038/s41586-022-05384-8

Chiroptically active pinwheel assemblies on substrates are formed by tetrahedral gold nanoparticles from the effective ‘compression’ of a perovskite-like, low-density phase, thereby enabling the manufacture of metastructured coatings with special chiroptical characteristics as identified by photon-induced near-field electron microscopy and chirality measures.

Nature Electronics, Published online: 28 November 2022; doi:10.1038/s41928-022-00874-z

Semiconductor polymer films that are based on a lateral-phase-separation-induced micromesh can be used to create transistors, complementary inverters and bilayer heterojunction photodetectors that can function under applied strains of up to 50%.

The symmetry-adapted artificial neural networks are designed to predict the interlayer magnetic exchange interactions in the twisted bilayer CrI3 (TBCI). These make the magnetic state simulations for TBCIs with arbitrary twist angles possible. The simulation results show that the K and T type TBCIs contain both the interlayer ferromagnetic and antiferromagnetic domains, and the T-TBCIs have rich robust skyrmion lattices.

Abstract

Magnetic skyrmions are topologically protected spin swirling vertices, which are promising in device applications due to their particle-like nature and excellent controlability. Magnetic skyrmions are extensively studied in a variety of materials and proposed to exist in the extreme 2D limit, i.e., in twisted bilayer CrI₃ (TBCI). Unfortunately, the magnetic states of TBCIs with small twist angles are disorderly distributed ferromagnetic and antiferromagnetic (AFM) domains in recent experiments, and thus the method to get rid of disorders in TBCIs is highly desirable. Here, intralayer exchange interactions up to the third nearest neighbors without empirical parameters and very accurate interlayer exchange interactions are used to study the magnetic states of TBCIs. The functions of interlayer exchange interactions obtained using first-principles calculations and stored in symmetry-adapted artificial neural networks are proposed. Based on these, the subsequent Landau–Lifshitz–Gillbert equation calculations explain the disorderly distributed FM-AFM domains in TBCIs with small twist angles and predict the orderly distributed skyrmions in TBCIs with large twist angles. This novel twisted 2D bilayer magnet can be used to design memory devices, monochromatic spin wave generators and many kinds of skyrmion lattices.

2D molybdenum compounds, by virtue of their high surface-to-volume ratio, unique electronic structure, and physicochemical properties, show great potential in electrocatalytic energy conversion applications. This review provides a comprehensive overview of the strategies for the synthesis and modulation of 2D molybdenum compounds and their applications in various electrocatalytic reactions that involve the cycles of water, carbon, and nitrogen.

Abstract

The development of advanced nanomaterials is urgent for electrocatalytic energy conversion applications. Recently, 2D nanomaterial-derived heterogeneous electrocatalysts have shown great promise for both fundamental research and practical applications owing to their extremely high surface-to-volume ratio and tunable geometric and electronic properties. Because of their unique electronic structure and physicochemical properties, molybdenum (Mo)-based 2D nanomaterials are emerging as one of the most attractive candidates among the nonprecious materials for electrocatalysts. This review provides a comprehensive overview of the recent advances in the synthesis and modulation of 2D Mo compounds for applications in electrocatalytic energy conversion. The categories based on different compositions and corresponding synthetic approaches of 2D Mo compounds are first introduced. Subsequently, various atomic/plane/synergistic engineering strategies, along with catalytic optimization in the electrochemical process that involves the cycles of water, carbon, and nitrogen, are discussed in detail. Finally, the current challenges and future opportunities for the development of 2D Mo-based electrocatalysts are proposed with the goal of shedding light on these promising 2D nanomaterials for electrocatalytic energy conversion.

This review article presents advances in 2D nanomaterial supported single metal atom catalysts (SACs) toward photo/electrocatalysis, with the special emphasis on the superiorities of 2D nanosheets as host materials. Advanced ex/in situ microscopic and spectroscopic approaches as well as rational design strategies of 2D-SACs, are comprehensively summarized. The future challenges and opportunities on the 2D nanosheets-supported SACs for photo/electrocatalysis are highlighted.

Abstract

Single-atom catalysts (SACs) attract intensive attention owing to their unmatched catalytic activities and high atom utilization. Besides metal species themselves, the substrates play a key role for the improvement of their catalytic performance by optimizing metal–support interactions and coordination structures. In the past years, various 2D nanomaterials have been employed to anchor single metal atoms for renewable energy technologies and other important industrial processes. Tremendous progress has been achieved in the development of 2D supported SACs for advanced energy conversion reactions. This article provides a comprehensive and critical review of up-to-date advances in the field of 2D supported SACs. The state-of-the-art characterizations including ex/in situ microscopic and spectroscopic techniques are summarized with the emphasis on their specific superiorities in identifying the reactive sites and reaction mechanisms, combined with theoretical calculations and experimental results. A brief overview of various reactions including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), two-electron oxygen reduction reaction (2e-ORR), carbon dioxide reduction (CO₂RR), and nitrogen reduction reaction (NRR) under the framework of electrocatalysis and photocatalysis, is presented on basis of versatile 2D nanomaterial supports. Last, the key challenges and opportunities in this rising field are highlighted.

Laser-Induced Graphene

In article number 2205158, Young-Jin Kim and co-workers comprehensively review the recent advances in three-dimensional porous laser-induced graphene and its applications in flexible electronics.

Solution-processed high-performance p-type WSe₂ thin-film transistor is successfully fabricated by Br₂-doping with a field-effect hole mobility of more than 27 cm² V⁻¹ s⁻¹, and a high on/off current ratio of ≈10⁷. The resulting complementary inverters with patterned p-type WSe₂ and n-type MoS₂ layered films reaches an ultra-high gain of 1280 under a driving voltage (V _DD) of 7 V.

Abstract

Semiconducting ink based on 2D single-crystal flakes with dangling-bond-free surfaces enables the implementation of high-performance devices on form-free substrates by cost-effective and scalable printing processes. However, the lack of solution-processed p-type 2D semiconducting inks with high mobility is an obstacle to the development of complementary integrated circuits. Here, a versatile strategy of doping with Br₂ is reported to enhance the hole mobility by orders of magnitude for p-type transistors with 2D layered materials. Br₂-doped WSe₂ transistors show a field-effect hole mobility of more than 27 cm² V⁻¹ s⁻¹, and a high on/off current ratio of ≈10⁷, and exhibits excellent operational stability during the on-off switching, cycling, and bias stressing testing. Moreover, complementary inverters composed of patterned p-type WSe₂ and n-type MoS₂ layered films are demonstrated with an ultra-high gain of 1280 under a driving voltage (V _DD) of 7 V. This work unveils the high potential of solution-processed 2D semiconductors with low-temperature processability for flexible devices and monolithic circuitry.

Anomalous Hall Effect

In article number 2206685, Lingfei Wang, Wenbin Wu, and co-workers report on the role of Ru doping in enhancing the anomalous Hall effect of ferromagnetic La_2/3Sr_1/3MnO₃ thin films. The Ru dopants embedded in the perovskite-structured La_2/3Sr_1/3MnO₃ can cause significant spin frustration and asymmetric scattering of spin-polarized electrons, thus leading to the enlarged anomalous Hall effect.

Advanced Materials, Volume 34, Issue 47, November 24, 2022.

A step toward the optical generation and control of coherent THz spin and lattice dynamics in 2D antiferromagnets. A coherent hybrid phonon–magnon mode is triggered in the 2D antiferromagnet FePS₃ by pumping below the band gap in the presence of an external magnetic field.

Abstract

Coherent THz optical lattice and hybridized phonon–magnon modes are triggered by femtosecond laser pulses in the antiferromagnetic van der Waals semiconductor FePS₃. The laser-driven lattice and spin dynamics are investigated in a bulk crystal as well as in a 380 nm-thick exfoliated flake as a function of the excitation photon energy, sample temperature and applied magnetic field. The pump-probe magneto-optical measurements reveal that the amplitude of a coherent phonon mode oscillating at 3.2 THz decreases as the sample is heated up to the Néel temperature. This signal eventually vanishes as the phase transition to the paramagnetic phase occurs, thus revealing its connection to the long-range magnetic order. In the presence of an external magnetic field, the optically triggered 3.2 THz phonon hybridizes with a magnon mode, which is utilized to excite the hybridized phonon–magnon mode optically. These findings open a pathway toward the optical control of coherent THz photo–magnonic dynamics in a van der Waals antiferromagnet, which can be scaled down to the 2D limit.

Nature Chemistry, Published online: 21 November 2022; doi:10.1038/s41557-022-01085-x

Inelastic hydrogen atom scattering from surfaces provides a good benchmark for the validity of the Born–Oppenheimer approximation in surface chemistry. Now it has been shown that hydrogen atoms colliding with a semiconductor surface can efficiently excite electrons above the surface bandgap, representing a clear example of the failure of the approximation.

Nature Electronics, Published online: 21 November 2022; doi:10.1038/s41928-022-00869-w

An activity-difference training approach, which employs 64 × 64 memristor arrays with integrated complementary metal–oxide–semiconductor control circuitry, can be used to train a deep neural network to efficiently classify Braille words.

The successfully synthesized lead-free 2D manganese-based (Mn-based) all-inorganic perovskite exhibits high pure crystal with a high carrier transport performance. After optimization, the maximum hole mobility of 2D perovskite field effect transistor (PeFETs) is 24 cm² V⁻¹ s⁻¹, and the on/off ratio is 10⁵ surpassing all reported PeFETs.

Abstract

2D perovskite is an organic–inorganic hybrid material with good photoelectric properties, generally prepared by using organic groups as isolation molecules. In this study, using manganese chloride and potassium halide as raw materials, all-inorganic 2D lead-free perovskites are prepared by the Bridgeman melting and cooling method. Different from the 2D perovskites synthesized by organic spacer molecules, the prepared all-inorganic 2D perovskites have smaller layer spacings and good crystallization performance due to the use of potassium halide as spacer molecules. They are direct bandgap semiconductors and their energy bandgaps are tuned by the different types of potassium halides. High degree orientation crystal thin films with (001) lattice plane parallel to silicon wafer substrate are prepared by double-source evaporation. The physical morphology of the films is characterized by grazing angle X-ray diffraction, transmission electron microscopy, and electron diffraction. The field effect transistors prepared from these 2D films show excellent electronic characteristics. The mobility of the optimized device is ≈24 cm² v⁻¹ s⁻¹ and the on/off ratio reaches 10⁵. This study reveals the potential of lead-free manganese 2D perovskite as a high-performance perovskite field effect transistor.

Near-infrared (NIR) mechanoluminescence (ML) in Cr³⁺ doped gallate spinel (ZnGa₂O₄:Cr³⁺, Zn₃Ga₂GeO₈:Cr³⁺) and gallate magnetoplumbite (SrGa₁₂O₁₉:Cr³⁺) is developed. With excellent environmental resistance, SrGa₁₂O₁₉:Cr³⁺ shows a broadband NIR light-emitting under mechano-/thermal-/photo- stimulation and has great potential in the field of bio-medicine and multidimensional anti-counterfeiting. This study provides more insights into broadband NIR ML based on Cr³⁺-doped inorganic materials.

Abstract

Mechanoluminescence (ML), as an optical response to deformation stimuli, shows great potential in high-end stress sensing, ultrasonic field visualization, and multidimensional anti-counterfeiting. However, processive practical applications in bio-medicine are constrained by the discovery of near-infrared (NIR) ML materials. Unlike lanthanides (Ln³⁺) with sharp multiplets, two kinds of Cr³⁺-doped NIR ML materials, gallate spinel (ZnGa₂O₄:Cr³⁺, Zn₃Ga₂GeO₈:Cr³⁺) and gallate magnetoplumbite (SrGa₁₂O₁₉:Cr³⁺) are here reported. Owing to the intrinsic cation antisite defects and cation vacancies in the matrix, these materials exhibit bright NIR ML under a relatively low load (20 N). In particular for SrGa₁₂O₁₉:Cr³⁺ (750 nm, peak; 100 nm, FWHM) with low persistent luminescence (PersL) interference, the ML behavior can be further rejuvenated under UV and sunlight irradiation. SrGa₁₂O₁₉:Cr³⁺ also shows bright NIR emission under photo- and thermo-stimulation. Owing to their excellent tissue penetration and concealment capability, NIR ML materials show great potential in the fields of bio-medicine and anti-counterfeiting.

Nature Nanotechnology, Published online: 21 November 2022; doi:10.1038/s41565-022-01248-4

Interfacing graphene with an antiferromagnetic insulator CrOCl enables the observation of strong interfacial coupling in the quantum Hall regime.

Nature Nanotechnology, Published online: 22 November 2022; doi:10.1038/s41565-022-01271-5

By applying strain to artificially reduce the crystal symmetry of a non-centrosymmetric two-dimensional material, a very large bulk photovoltaic effect is uncovered with anisotropic properties that reflect its non-linear origins.

In this study, the relationship between excited-state processes and electroluminescence efficiencies in interface exciplex organic light-emitting diodes (OLEDs), is systematically investigated. Nearly 100% exciton utilization is observed when thermally activated delayed fluorescence (4CzPN) emitter is doped in the active layer of the interface exciplex OLEDs by simultaneously activating the Förster and Dexter energy transfer channels and suppressing the triplet-triplet annihilation process.

Abstract

Interface exciplex represents a promising host material for organic light-emitting diodes (OLEDs) with barrier-free charge injection and highly confined recombination region. However, the efficiency of radiative recombination in pristine exciplex is usually low and needs to be improved by doping various emitters. In this study, the interface exciplex OLEDs doped with fluorescence, phosphorescence, and thermally activated delayed fluorescence (TADF) emitters is fabricated to investigate the relationship between their excited-state properties and electroluminescence efficiencies. A maximum external quantum efficiency of 20% is achieved in interface exciplex OLEDs doped with TADF emitter, which corresponds to nearly 100% exciton utilization and is superior to those of fluorescence and phosphorescence emitters. Furthermore, optical spectroscopy and magneto-electroluminescence method are used to study the advantages of TADF emitter in interface exciplex host. The large dipole of TADF emitter is beneficial for harvesting energy from the charge-transfer state at the interface, and its reverse intersystem crossing avoids the accumulation of triplet excitons that leads to triplet-triplet annihilation in interface exciplex OLEDs. These results demonstrate that the photophysical process needs to be carefully considered in designing high-performance emitters for exciplex host materials, and it may bring in-depth understanding on improving exciton utilization and electroluminescence efficiency in interface exciplex OLEDs.

Inspired by brain-centered perception processes, a machine-learning-assistant early fire perception system is demonstrated that can demodulate multiple fire signals and achieve early warning, fire cause identification, and evacuation advice provides. To the best of authors knowledge, this is the first fire perception system featuring real-time processing abilities with achieving early warning, fire cause identification, and evacuation advice provides.

Abstract

The continuation of human civilization has always been accompanied by symbiosis and confrontation with fire. Particularly, humans can comprehensively recognize fire situations based on various sensory receptors in organs (eyes, skin, nose, etc.), further forming a sound fire perception system by in-the-brain recording, modeling, and understanding fire behaviors, leading to the most accurate fire treatments. If a sensing perception system can mimic human perceptual behavior and carry out real-time fire recognition, such an active defense system can achieve real fire safety. Here, inspired by the brain-centered perception system, an early-fire perception system enabled by a VO₂-based temperature-flame-modulated optical switch, and a machine-learning-assistant demodulation algorithm is reported. This approach creates real-time monitoring composed of early fire warning (1 s for candle flame and 4 s for 130 °C heat flow), fire cause recognition (95.7% accuracy in identification), and evacuation advice provision, advancing the technologies in the perception system that enable future sensors the comprehensive perception capability for fire state.

A self-encrypted all-optical memory with ultrahigh switching contrast is realized in Y₂O₃:Eu³⁺–Au. All-optical information revisible writing, reading, encryption, and re-writting are realized through a simple change of the irradiation light power. This work not only provides insight into the unique thermal response of the plasmon resonance in the composite structure but also offers good candidates for self-encrypted binary information storage.

Abstract

All-optical responsive nanomaterials, which can rapidly switch between two stable states, have been regarded as the next-generation memories due to their potential to realize binary information storage and implement on-chip, integrated photonic neuromorphic systems. Rare earth oxides are preeminent candidates owing to their extraordinary luminescent stability and narrow optical transitions. However, due to the lack of simple and effective optical switches, it is difficult to realize all-optical data storage, encoding, and retrieval by pure rare earth-doped luminescent nanoparticles. Here, a rapid and high-contrast of 10⁴ luminescent switching of Y₂O₃:Eu³⁺ nanoparticle between the enhancement and quenching states is achieved by employing the strong light confinement and ultrafast thermal response of localized surface plasmon resonance. A self-encrypted all-optical memory is presented with optical information writing, encryption, reading, and re-writing, and a high-sensitivity synaptic response of emitters to frequency and light intensity flux, which can be harnessed to encrypt information flows and promote convenient and high-security information encryption. Such a convenient and secure plasmonic thermally assisted self-encrypting luminescent switch paves the way for constructing high-performance stimuli-responsive rare earth oxide crystals on demand and expanding their applications in various data encryption, anti-counterfeiting, and rewritable colouration devices.

Combined real-space observation and anisotropic magnetoresistance (AMR) detection of dipolar skyrmion chains determine that AMR cannot distinguish the skyrmions with different helicities, AMR can detect a single skyrmion chain with the amplitude determined by the skyrmion count, and AMR can detect the presence of a single skyrmion.

Abstract

Magnetic skyrmions are localized particle-like nontrivial swirls that are promising in building high-performance topological spintronic devices. The read-out functions in skyrmionic devices require the translation of magnetic skyrmions to electrical signals. Here, combined real-space magnetic imaging and anisotropic magnetoresistance studies on dipolar skyrmions are reported. A single skyrmion chain and single skyrmion are observed using Lorentz transmission electron microscopy imaging. Meanwhile, the field, helicity, and skyrmion count dependence of anisotropic magnetoresistance of the Fe₃Sn₂ nanostructures are obtained simultaneously. These results demonstrate that the anisotropic magnetoresistance of skyrmions is independent of the helicity and proportional to the skyrmion count. This study promotes read-out operations in skyrmion-based spintronic devices.

Using van der Waals epitaxial method, ultrathin topological insulator Ag₂Te single crystals are synthesized. The Ag₂Te single crystals exhibit p-type conduction behavior with high carrier mobility of 3336 cm² V^–1 s^–1 at room temperature. A self-driven broad-spectrum high-performance photodetector with high responsivity, high on/off ratio, and fast response speed is obtained based Ag₂Te/WSe₂ heterojunction_.

Abstract

β-Ag₂Te has attracted considerable attention in the application of electronics and optoelectronics due to its narrow bandgap, high mobility, and topological insulator properties. However, it remains a significant challenge to synthesize 2D Ag₂Te because of the non-layered structure of Ag₂Te. Herein, the synthesis of large-size, ultrathin single crystal topological insulator 2D Ag₂Te via the van der Waals epitaxial method for the first time is reported. The 2D Ag₂Te crystal exhibits p-type conduction behavior with high carrier mobility of 3336 cm² V⁻¹ s⁻¹ at room temperature. Taking advantage of the high mobility and perfect electron structure of Ag₂Te, the Ag₂Te/WSe₂ heterojunctions are fabricated via mechanical stacking and show an ultrahigh rectification ratio of 2 × 10⁵. Ag₂Te/WSe₂ photodetector also exhibits self-driven properties with a fast response speed (40 µs/60 µs) in the near-infrared region. High responsivity (219 mA W⁻¹) and light ON/OFF ratio of 6 × 10⁵ are obtained under the photovoltaic mode. The overall performance of the Ag₂Te/WSe₂ photodetector is significantly competitive among all reported 2D photodetectors. These results indicate that 2D Ag₂Te is a promising candidate for future electronic and optoelectronic applications.

The rich theoretical framework of bandgaps is delineated in structure-borne-sound metamaterials and phononic crystals, while highlighting elastic bandgap engineering for contemporary applications such as surface acoustic wave devices, optomechanics, seismic wave control, and high Q-factor sensors. This review also provides a roadmap for future directions for these artificial functional materials.

Abstract

In solid state physics, a bandgap (BG) refers to a range of energies where no electronic states can exist. This concept was extended to classical waves, spawning the entire fields of photonic and phononic crystals where BGs are frequency (or wavelength) intervals where wave propagation is prohibited. For elastic waves, BGs are found in periodically alternating mechanical properties (i.e., stiffness and density). This gives birth to phononic crystals and later elastic metamaterials that have enabled unprecedented functionalities for a wide range of applications. Planar metamaterials are built for vibration shielding, while a myriad of works focus on integrating phononic crystals in microsystems for filtering, waveguiding, and dynamical strain energy confinement in optomechanical systems. Furthermore, the past decade has witnessed the rise of topological insulators, which leads to the creation of elastodynamic analogs of topological insulators for robust manipulation of mechanical waves. Meanwhile, additive manufacturing has enabled the realization of 3D architected elastic metamaterials, which extends their functionalities. This review aims to comprehensively delineate the rich physical background and the state-of-the art in elastic metamaterials and phononic crystals that possess engineered BGs for different functionalities and applications, and to provide a roadmap for future directions of these manmade materials.