Jing Zhang

This work reports on a new strategy, using semiconducting monolayers of Si₂Te₂ and Sb₂Te₃, for the epitaxial growth of high-density lateral heterojunction arrays with tunable interfacial band alignment. Scanning tunneling microscopy/spectroscopy measurements demonstrate the continuous lattice of the two-dimensional Si₂Te₂/Sb₂Te₃ lateral heterojunctions and directly reveal the tailored type-II band bending at the interface.

Abstract

Two-dimensional (2D) lateral heterojunction arrays, characterized by well-defined electronic interfaces, hold significant promise for advancing next-generation electronic devices. Despite this potential, the efficient synthesis of high-density lateral heterojunctions with tunable interfacial band alignment remains a challenging. Here, a novel strategy is reported for the fabrication of lateral heterojunction arrays between monolayer Si₂Te₂ grown on Sb₂Te₃ (ML-Si₂Te₂@Sb₂Te₃) and one-quintuple-layer Sb₂Te₃ grown on monolayer Si₂Te₂ (1QL-Sb₂Te₃@ML-Si₂Te₂) on a p-doped Sb₂Te₃ substrate. The site-specific formation of numerous periodically arranged 2D ML-Si₂Te₂@Sb₂Te₃/1QL-Sb₂Te₃@ML-Si₂Te₂ lateral heterojunctions is realized solely through three epitaxial growth steps of thick-Sb₂Te₃, ML-Si₂Te₂, and 1QL-Sb₂Te₃ films, sequentially. More importantly, the precisely engineering of the interfacial band alignment is realized, by manipulating the substrate's p-doping effect with lateral spatial dependency, on each ML-Si₂Te₂@Sb₂Te₃/1QL-Sb₂Te₃@ML-Si₂Te₂ junction. Atomically sharp interfaces of the junctions with continuous lattices are observed by scanning tunneling microscopy. Scanning tunneling spectroscopy measurements directly reveal the tailored type-II band bending at the interface. This reported strategy opens avenues for advancing lateral epitaxy technology, facilitating practical applications of 2D in-plane heterojunctions.

The crystal structure and optical properties of the van der Waals layered CuInP₂Se₆ are systematically studied. A dual-function detector based on 2D CuInP₂Se₆, exhibiting an ultralow and stable dark current, is fabricated. This detector demonstrates remarkable sensitivity in detecting UV-vis light and X-rays, and it is successfully employed in high-resolution image sensing applications.

Abstract

Metal thio(seleno)phosphates are renowned for their multifaceted physical characteristics and versatile applications, particularly in optoelectronics. In detection applications, a low and stable dark current is crucial, enhancing the sensitivity and signal-to-noise ratio of detectors. Herein, a van der Waals layered material has synthesized, CuInP₂Se₆. Despite its nanometric scale, 2D CuInP₂Se₆ detector transcends the conventional absorption inefficiencies tied to ultrathin materials. It delivers exceptional ultraviolet–visible detection, characterized by an ultralow, stable dark current of 150 fA, and a noise power density of 27.7 fA Hz^−1/2 at room temperature. The in-depth investigation reveals a responsivity of 4.47 A W⁻¹, an external quantum efficiency of 1369%, a special detectivity of 1.44 × 10¹³ Jones, and a rapid response speed of 280 µs, positioning it at the pinnacle of 2D photodetector performance. The CuInP₂Se₆’s ultralow, stable dark current paves the way for X-ray detection, achieving an unprecedented sensitivity of 1.32 × 10⁵ µC Gy_air ⁻¹ cm⁻² and a low detection limit of 0.15 µGy_air s⁻¹. Furthermore, 2D CuInP₂Se₆ detector exhibits a remarkable image-sensing capability, adeptly capturing intricate patterns with high resolution. This discovery indicates its promise in revolutionizing integrated micro/nano optoelectronic devices, opening avenues for advancements in light and X-ray detection and imaging technologies.

In this paper, the coexistence of superconductivity and topological band structure is reported in ANbS₂ (A = In, Bi, and Pb). The superconductivity is evidenced by electrical transport and magnetization behavior. First-principles calculations reveal the topological semimetal properties of ANbS₂. The coexistence positions ANbS₂ as a promising platform for exploring topological superconductors.

Abstract

The research on systems with coexistence of superconductivity and nontrivial band topology has attracted widespread attention. However, the limited availability of material platforms severely hinders the research progress. Here, it reports the first experimental synthesis and measurement of high-quality single crystal van der Waals transition-metal dichalcogenide InNbS₂, revealing it as a topological nodal line semimetal with coexisting superconductivity. The temperature-dependent measurements of magnetization susceptibility and electrical transport show that InNbS₂ is a type-II superconductor with a transition temperature T _c of 6 K. First-principles calculations predict multiple topological nodal ring states close to the Fermi level in the presence of spin–orbit coupling. Similar features are also observed in the as-synthesized BiNbS₂ and PbNbS₂ samples. This work provides new material platforms ANbS₂ (A = In, Bi, and Pb) and uncovers their intriguing potential for exploring the interplay between superconductivity and band topology.

Nature Electronics, Published online: 02 February 2024; doi:10.1038/s41928-024-01118-y

Polycrystalline thin films of elemental bismuth exhibit a room-temperature nonlinear transverse voltage due to geometric effects of surface electrons that is tunable and can be extended to efficient high-harmonic generation at terahertz frequencies.

The molybdenum telluride (MoTe₂) based photoelectrochemical photodetector is fabricated by liquid phase exfoliation accompanied by the electrophoretic deposited method. This MoTe₂-based photodetector shows a broadband detection in ultraviolet–near-infrared band, long-term stability within 18 000 s, and fast response in millisecond-level. More importantly, this photodetector shows excellent flexibility and folding resistance, as well as omnidirectional detection capability.

Abstract

Flexible broadband photodetectors are desired but challenging to be fabricated for next-generation wearable intelligent optoelectronic devices. Considering the narrow bandgap and strong light absorption, molybdenum telluride (MoTe₂) based photoelectrochemical photodetectors are successfully assembled by liquid phase exfoliation accompanied with the electrophoretic deposited method. This MoTe₂-based photodetector shows a broadband detection in ultraviolet–near-infrared band, long-term stability within 18000 s, and fast response in millisecond-level (response time≈19 ms, recovery time≈26 ms). More importantly, even though the MoTe₂ photodetector is bent and twisted at a high degree for several hundred times, it still shows excellent flexibility with stable on-off switching characteristics. Additionally, this photodetector displays a good response for rotation angles in the range from 0° to 360°, and the extracted I _ph maintain almost the same value approximately 0.97 µA cm⁻², suggesting an omnidirectional detection capability. This work demonstrates the proposed flexible photoanode shows a great potential in future broadband omnidirectional detection systems.

A BiOCl-assisted chemical vapor deposition method is established to synthesize ultrathin p-type semiconductor α-In₂Te₃ nanoflakes at low temperature. With strong second harmonic generation and a narrow bandgap, it displays a high mobility of 18 cm² V⁻¹s⁻¹ and a broadband photoresponse ranging from 405 nm to 1064 nm, with response time of τ _rise = 1 ms.

Abstract

2D A2IIIB3VI${\mathrm{A}}_2^{{\mathrm{III}}}{\mathrm{B}}_3^{{\mathrm{VI}}}$ compounds (A = Al, Ga, In, and B = S, Se, and Te) with intrinsic structural defects offer significant opportunities for high-performance and functional devices. However, obtaining 2D atomic-thin nanoplates with non-layered structure on SiO₂/Si substrate at low temperatures is rare, which hinders the study of their properties and applications at atomic-thin thickness limits. In this study, the synthesis of ultrathin, non-layered α-In₂Te₃ nanoplates is demonstrated using a BiOCl-assisted chemical vapor deposition method at a temperature below 350 °C on SiO₂/Si substrate. Comprehensive characterization results confirm the high-quality single crystal is the low-temperature cubic phase α-In₂Te₃ , possessing a noncentrosymmetric defected ZnS structure with good second harmonic generation. Moreover, α-In₂Te₃ is revealed to be a p-type semiconductor with a direct and narrow bandgap value of 0.76 eV. The field effect transistor exhibits a high mobility of 18 cm² V⁻¹ s⁻¹, and the photodetector demonstrates stable photoswitching behavior within a broadband photoresponse from 405 to 1064 nm, with a satisfactory response time of τ_rise = 1 ms. Notably, the α-In₂Te₃ nanoplates exhibit good stability against ambient environments. Together, these findings establish α-In₂Te₃ nanoplates as promising candidates for next-generation high-performance photonics and electronics.

In this review, luminescent properties of 2D tin halide perovskites are focused on. A unique dual emission phenomenon in 2D tin halide perovskites with several types of possible reasons is highlighted and summarized. In addition, recent progress in 2D tin-halide-perovskite-based light-emitting diodes are overviewed. Some possible approaches for solving the problems of oxidation inhibition and for improving efficiency in 2D tin halide perovskites are also put forward.

Abstract

Lead halide perovskites are widely used and intensively studied in optoelectronic devices due to their superior properties. However, the toxicity of Pb hinders the industrialization of perovskite optoelectronic devices. Sn has a similar electronic structure to Pb, thus has been widely studied as an alternative to Pb-based perovskite optoelectronics in recent years. In this review, the research progress in luminescent properties and synthesis methods of 2D tin halide perovskites are summarized. It is also highlight a unique dual emission phenomenon in 2D tin halide perovskites and summarize several types of possible luminous mechanisms. At last, the recent development of 2D tin halide perovskites based light-emitting diodes are also overviewed, and the challenges of oxidative inhibition and efficiency improvement in 2D tin halide perovskites are discussed. This review is expected to provide a comprehensive perspective on luminescent properties and light-emitting diode applications of 2D tin halide perovskites.

The morphology of ZnSe epilayers on InP NCs is controlled, ranging from tetrapod to spherical InP/ZnSe heterostructured NCs, under the guidance of DFT calculations. The expanded morphology envelope permits InP/ZnSe heterostructured NCs to customize their photophysical characteristics from stable and pure emission to environment-sensitive ones, which will prompt their practical use in a range of photonic applications.

Abstract

The morphology of heterostructured semiconductor nanocrystals (h-NCs) dictates the spatial distribution of charge carriers and their recombination dynamics and/or transport, which are the main performance indicators of photonic applications utilizing h-NCs. The inability to control the morphology of heterovalent III-V/II-VI h-NCs composed of heavy-metal-free elements hinders their practical use. As a case study of III-V/II-VI h-NCs, the growth control of ZnSe epilayers on InP NCs is demonstrated here. The anisotropic morphology in InP/ZnSe h-NCs is attributed to the facet-dependent energy costs for the growth of ZnSe epilayers on different facets of InP NCs, and effective chemical means for controlling the growth rates of ZnSe on different surface planes are demonstrated. Ultimately, this article capitalizes on the controlled morphology of InP/ZnSe h-NCs to expand their photophysical characteristics from stable and pure emission to environment-sensitive one, which will facilitate their use in a variety of photonic applications.

This review provides a comprehensive and systematic overview of advancements in 2D transition metal dichalcogenides (2D TMDs) surface-enhanced Raman scattering (SERS) substrates, detailing the enhancement mechanisms, material exploration, material engineering techniques, and practical applications. It also discusses the challenges and future prospects of creating high-performance 2D TMDs SERS substrates and outlines potential directions for achieving significant breakthroughs in practical applications.

Abstract

Surface-enhanced Raman spectroscopy (SERS) is an ultrasensitive surface analysis technique that is widely used in chemical sensing, bioanalysis, and environmental monitoring. The design of the SERS substrates is crucial for obtaining high-quality SERS signals. Recently, 2D transition metal dichalcogenides (2D TMDs) have emerged as high-performance SERS substrates due to their superior stability, ease of fabrication, biocompatibility, controllable doping, and tunable bandgaps and excitons. In this review, a systematic overview of the latest advancements in 2D TMDs SERS substrates is provided. This review comprehensively summarizes the candidate 2D TMDs SERS materials, elucidates their working principles for SERS, explores the strategies to optimize their SERS performance, and highlights their practical applications. Particularly delved into are the material engineering strategies, including defect engineering, alloy engineering, thickness engineering, and heterojunction engineering. Additionally, the challenges and future prospects associated with the development of 2D TMDs SERS substrates are discussed, outlining potential directions that may lead to significant breakthroughs in practical applications.

An in-depth examination of 2D FeFET advancements over recent years is provided in this review, including the working mechanism, structural evolution, as well as the diverse applications. Moreover, a summary of ongoing research efforts and offers further perspectives on the emerging opportunities for 2D FeFET is concluded.

Abstract

The rapid development in information technologies necessitates rapid advancements of their supporting hardware. In particular, new computing paradigms are needed to overcome the bottleneck of traditional von Neumann architecture. Bottom-up innovation, especially at the materials and devices level, has the potential to disrupt existing technologies through their emergent phenomena. As a new type of conceptual device, 2D ferroelectric field-effect transistor (FeFET) is highly sought after due to its potential integration with modern semiconductor processes. Its low power consumption, area efficiency, and ultra-fast operation provide an extra edge over traditional technologies. This review highlights recent developments in 2D FeFET, covering their device construction, working mechanisms, 2D ferroelectric polarization mechanism, multi-functional applications and prospects. In particular, the combination of 2D semiconductor and ferroelectric dielectric materials for multi-functionality applications is discussed. This includes non-volatile memories (NVM), neural network computing, non-volatile logic operation, and photodetectors. As a novel device platform, 2D semiconductor and ferroelectric interfaces are bestowed with a plethora of emergent physical mechanisms and applications.

Room-temperature Néel skyrmions in Fe₃GaTe₂ are observed through Lorentz transmission electron microscopy . Upon an optimized field cooling procedure, zero-field skyrmion lattices are successfully generated in nanoflakes with an extended thickness range. Significantly, these skyrmion lattices remain stable up to 355 K, setting a new record for the highest temperature at which skyrmions can be hosted.

Abstract

2D van der Waals (vdW) ferromagnetic crystals are a promising platform for innovative spintronic devices based on magnetic skyrmions, thanks to their high flexibility and atomic thickness stability. However, room-temperature skyrmion-hosting vdW materials are scarce, which poses a challenge for practical applications. In this study, a chemical vapor transport (CVT) approach is employed to synthesize Fe₃GaTe₂ crystals and room-temperature Néel skyrmions are observed in Fe₃GaTe₂ nanoflakes above 58 nm in thickness through in situ Lorentz transmission electron microscopy (L-TEM). Upon an optimized field cooling procedure, zero-field hexagonal skyrmion lattices are successfully generated in nanoflakes with an extended thickness range (30–180 nm). Significantly, these skyrmion lattices remain stable up to 355 K, setting a new record for the highest temperature at which skyrmions can be hosted. The research establishes Fe₃GaTe₂ as an emerging above-room-temperature skyrmion-hosting vdW material, holding great promise for future spintronics.

This study presents the epitaxial growth and stacking sequences of InTe, an intriguing material within III–VI metal chalcogenides. Utilizing aberration-corrected STEM, the interlayer stacking modes are directly revealed, leading to the identification of a new polytype. STEM analysis provided evidence for strong interlayer coupling in the new polytype, with layer-by-layer deposition identified as the mechanism behind the unconventional stacking order.

Abstract

III–VI metal chalcogenides have garnered considerable research attention as a novel group of layered van der Waals materials because of their exceptional physical properties and potential technological applications. Here, the epitaxial growth and stacking sequences of InTe is reported, an essential and intriguing material from III–VI metal chalcogenides. Aberration-corrected scanning transmission electron microscopy (STEM) is utilized to directly reveal the interlayer stacking modes and atomic structure, leading to a discussion of a new polytype. Furthermore, correlations between the stacking sequences and interlayer distances are substantiated by atomic-resolution STEM analysis, which offers evidence for strong interlayer coupling of the new polytype. It is proposed that layer-by-layer deposition is responsible for the formation of the unconventional stacking order, which is supported by ab initio density functional theory calculations. The results thus establish molecular beam epitaxy as a viable approach for synthesizing novel polytypes. The experimental validation of the InTe polytype here expands the family of materials in the III–VI metal chalcogenides while suggesting the possibility of new stacking sequences for known materials in this system.

Resolving interlayer coupling in 2D heterostructures is difficult, especially in the presence of disorders. Femtosecond nano-probe imaging combining coherent four-wave mixing and incoherent two-photon photoluminescence is applied to resolve the interlayer coupling in WSe₂ /graphene heterostructures. Using hBN spacer layers, it is discovered that energy transfer dominates the interlayer coupled response, with a timescale of ≈0.35 ps.

Abstract

The emergent electronic, spin, and other quantum properties of 2D heterostructures of graphene and transition metal dichalcogenides are controlled by the underlying interlayer coupling and associated charge and energy transfer dynamics. However, these processes are sensitive to interlayer distance and crystallographic orientation, which are in turn affected by defects, grain boundaries, or other nanoscale heterogeneities. This obfuscates the distinction between interlayer charge and energy transfer. Here, nanoscale imaging in coherent four-wave mixing (FWM) and incoherent two-photon photoluminescence (2PPL) is combined with a tip distance-dependent coupled rate equation model to resolve the underlying intra- and inter-layer dynamics while avoiding the influence of structural heterogeneities in mono- to multi-layer graphene/WSe₂ heterostructures. With selective insertion of hBN spacer layers, it is shown that energy, as opposed to charge transfer, dominates the interlayer-coupled optical response. From the distinct nano-FWM and -2PPL tip-sample distance-dependent modification of interlayer and intralayer relaxation by tip-induced enhancement and quenching, an interlayer energy transfer time of τET≈(0.35−0.15+0.65)$\tau _{\rm ET} \approx (0.35^{+0.65}_{-0.15})$ ps consistent with recent reports is derived. As a local probe technique, this approach highlights the ability to determine intrinsic sample properties even in the presence of large sample heterogeneity.

Nature Photonics, Published online: 26 January 2024; doi:10.1038/s41566-024-01377-3

An optical readout technique for the chemical potential of an arbitrary two-dimensional material is realized using a monolayer transition metal dichalcogenide semiconductor sensor whose optical response sharply depends on the chemical potential.

Nature Communications, Published online: 26 January 2024; doi:10.1038/s41467-024-44972-2

Here, the authors report the characterization of stable few-layer PdSe2 transistors encapsulated in hexagonal boron nitride, showing field effect mobilities up to 700 cm2/Vs at room temperature and signatures of an 8-fold spin-valley degeneracy of the magnetotransport quantum oscillations at cryogenic temperatures.

Current-induced magnetic skyrmion motion is directly visualized in 2D van der Waals (vdW) ferromagnet Fe₃GaTe₂ (FGaT) at room temperature. The electrical pulse can thermally generate the skyrmions under an external magnetic field. In addition, magnetic skyrmions are effectively driven by electrical current. The results demonstrate the feasibility of operating skyrmion devices at room temperature using 2D materials.

Abstract

The recent discovery of room-temperature ferromagnetism in 2D van der Waals (vdW) materials, such as Fe₃GaTe₂ (FGaT), has garnered significant interest in offering a robust platform for 2D spintronic applications. Various fundamental operations essential for the realization of 2D spintronics devices are experimentally confirmed using these materials at room temperature, such as current-induced magnetization switching or tunneling magnetoresistance. Nevertheless, the potential applications of magnetic skyrmions in FGaT systems at room temperature remain unexplored. In this work, the current-induced generation of magnetic skyrmions in FGaT flakes employing high-resolution magnetic transmission soft X-ray microscopy is introduced, supported by a feasible mechanism based on thermal effects. Furthermore, direct observation of the current-induced magnetic skyrmion motion at room temperature in FGaT flakes is presented with ultra-low threshold current density. This work highlights the potential of FGaT as a foundation for room-temperature-operating 2D skyrmion device applications.

A strategy to achieve 100% activation is reported of atoms on the basal plane of 2D layered materials by constructing an interlayer biatomic bridge. New gap states at the Fermi level are introduced and interlayer conductivity is enhanced in this catalyst. Exposed basal plane atoms are optimized to a state favorable for adsorbing catalytic intermediates.

Abstract

2D layered materials are regarded as prospective catalyst candidates due to their advantageous atomic exposure ratio. Nevertheless, the predominant population of atoms residing on the basal plane with saturated coordination, exhibit inert behavior, while a mere fraction of atoms located at the periphery display reactivity. Here, a novel approach is reported to attain complete atom activation in 2D layered materials through the construction of an interlayer biatomic pair bridge. The atoms in question have been strategically optimized to achieve a highly favorable state for the adsorption of intermediates. This optimization results from the introduction of new gap states around the Fermi level. Moreover, the presence of the interlayer bridge facilitates the electron transfer across the van der Waals gap, thereby enhancing the reaction kinetics. The hydrogen evolution reaction exhibits an impressive ultrahigh current density of 2000 mA cm⁻² at 397 mV, surpassing the pristine MoS₂ by approximately two orders of magnitude (26 mA cm⁻² at 397 mV). This study provides new insights for enhancing the efficacy of 2D layered catalysts.

A new persistent photocurrent mechanism based on ion motion and ion-exciton coupling is proposed in two dimensional perovskites. The special charge carrier dynamics lead to the bio-plausible synaptic characteristics of the photodetectors. The light-tunable synaptic plasticity enables not only to realize image preprocessing, but also effectively recognizes target images by learning critical features.

Abstract

Neuromorphic visual sensors (NVS) based on photonic synapses hold a significant promise to emulate the human visual system. However, current photonic synapses rely on exquisite engineering of the complex heterogeneous interface to realize learning and memory functions, resulting in high fabrication cost, reduced reliability, high energy consumption and uncompact architecture, severely limiting the up-scaled manufacture, and on-chip integration. Here a photo-memory fundamental based on ion-exciton coupling is innovated to simplify synaptic structure and minimize energy consumption. Due to the intrinsic organic/inorganic interface within the crystal, the photodetector based on monolithic 2D perovskite exhibits a persistent photocurrent lasting about 90 s, enabling versatile synaptic functions. The electrical power consumption per synaptic event is estimated to be≈1.45 × 10⁻¹⁶ J, one order of magnitude lower than that in a natural biological system. Proof-of-concept image preprocessing using the neuromorphic vision sensors enabled by photonic synapse demonstrates 4 times enhancement of classification accuracy. Furthermore, getting rid of the artificial neural network, an expectation-based thresholding model is put forward to mimic the human visual system for facial recognition. This conceptual device unveils a new mechanism to simplify synaptic structure, promising the transformation of the NVS and fostering the emergence of next generation neural networks.

This work has constructed a novel intelligent programmable photonic gel composed of cellulose nanocrystals and acrylamide, which can achieve reversible switching of mechanical properties and optical signals as required. This is a successful example of the application of cellulose nanocrystals chiral structure in switchable supramolecular network materials.

Abstract

The microscopically structural switching of supramolecular networks endows programmable gel materials with dynamic hiding properties and functionalities. However, the reconstruction of supramolecular network will destroy the programming information imprinted on the original network structure, making it difficult to restore to the original state. Here, a novel intelligent programmable photonic gel composed of cellulose nanocrystals (CNC) and acrylamide is constructed. The mechanical properties and optical signals of gel can be switched reversibly on demand by reasonably designing the winding and compression between molecular structures. Under this conversion mechanism, the rigid “skeleton” constructed from the CNC chiral structure perfectly acts as the coding substrate. Importantly, even after multiple dynamic switching of the supramolecular network, the encoded information can be displayed completely and accurately on the CNC chiral structure in the stretched state. In addition, the 5D controllable conversion of stiffness, transparency, stretchability, color, and shape greatly improves the security and confidentiality of the encoded information inside the gel. This is a successful example of the application of CNC chiral structure in switchable supramolecular network materials. It is believed that the flexible variability and advanced camouflage give the intelligent gel the potential to be used in a wider range of practical scenarios.

2D materials are emerging as promising candidates for fabricating high-performance photodetectors. In this review, recent progress on 2D materials-based photothermoelectric detectors is reviewed. The physical detection mechanism and the photothermoelectric properties of 2D materials are summarized. Strategies to improve the photodetection performance of PTE detectors are reviewed. Finally, the challenges and prospects for future research are also provided.

Abstract

2D materials, with outstanding optical, thermal, and electric properties, are emerging as promising candidates for fabricating high-performance photodetectors. Recently, impressive progresses have been made in this area and some challenges are remaining to improve the properties of photodetectors. As one important part in the mainstream photodetection mechanisms, photothermoelectric (PTE) effect is showing unique priorities in fabricating advanced photodetectors, especially broadband detection operating in the mid-infrared and terahertz spectral regime. Here, recent progress on PTE photodetectors based on layered 2D materials is reviewed. The physical mechanism of PTE effect is first discussed and then the optical and thermoelectric properties of various 2D materials are analyzed. Furthermore, strategies to improve the photodetection performance of PTE detectors are summarized in two major categories including enhanced photothermal conversion and thermoelectric conversion processes. Finally, the challenges and prospects for future research in 2D thermoelectric materials and PTE detectors are also provided.

A fully memristive elementary motion detector (M-EMD) is proposed to emulate the biological vision system. Inspired by the structure and function of the biological motion-detecting neural circuit, the detector achieves agile and efficient motion detection using a simple configuration composed only of memristors. The proposed detector is applicable to a motion-detecting element for edge-level neuromorphic computing.

Abstract

Insects can efficiently perform object motion detection via a specialized neural circuit, called an elementary motion detector (EMD). In contrast, conventional machine vision systems require significant computational resources for dynamic motion processing. Here, a fully memristive EMD (M-EMD) is presented that implements the Hassenstein–Reichardt (HR) correlator, a biological model of the EMD. The M-EMD consists of a simple Wye (Y) configuration, including a static resistor, a dynamic memristor, and a Mott memristor. The resistor and dynamic memristor introduce different signal delays, enabling spatio-temporal signal integration in the subsequent Mott memristor, resulting in a direction-selective response. In addition, a neuromorphic system is developed employing the M-EMDs to predict a lane-changing maneuver by vehicles on the road. The system achieved a high accuracy (> 87%) in predicting future lane-changing maneuvers on the Next Generation Simulation (NGSIM) dataset while reducing the computational cost by 92.9% compared to the conventional neuromorphic system without the M-EMD, suggesting its strong potential for edge-level computing.

The multi-output state of the resistance is acquired by a pure current strategy based on the manipulation of domain wall number by pulse current under zero magnetic field in the 2D ferromagnet Fe₃GeTe₂. The multi-output properties can be utilized in the pattern recognition in the neuron computing trained by National Institute of Standards and Technology dataset.

Abstract

Controlling the multi-state switching is significantly essential for the extensive utilization of 2D ferromagnet in magnetic racetrack memories, topological devices, and neuromorphic computing devices. The development of all-electric functional nanodevices with multi-state switching and a rapid reset remains challenging. Herein, to imitate the potentiation and depression process of biological synapses, a full-current strategy is unprecedently established by the controllable resistance-state switching originating from the spin configuration rearrangement by domain wall number modulation in Fe₃GeTe₂. In particular, a strong correlation is uncovered in the reduction of domain wall number with the corresponding resistance decreasing by in-situ Lorentz transmission electron microscopy. Interestingly, the magnetic state is reversed instantly to the multi-domain wall state under a single pulse current with a higher amplitude, attributed to the rapid thermal demagnetization by simulation. Based on the neuromorphic computing system with full-current-driven artificial Fe₃GeTe₂ synapses with multi-state switching, a high accuracy of ≈91% is achieved in the handwriting image recognition pattern. The results identify 2D ferromagnet as an intriguing candidate for future advanced neuromorphic spintronics.

A novel strategy is employed to achieve a giant negative photoconductance (NPC) effect in a graphene/AgBiP₂Se₆/graphene van der Waals vertical heterostructure device by applying a high drain-source voltage bias. Remarkably, this device demonstrates an exceptionally high negative responsivity (R) of 4.9 × 10⁵ A W⁻¹, surpassing the previous records for NPC photodetectors.

Abstract

The positive photoconductive (PPC) effect is a well-established primary detection mechanism employed by photodetectors. In contrast, the negative photoconductive (NPC) effect is not extensively investigated thus far, and research on the NPC effect is still in its early stage. Herein, a quaternary van der Waals material, AgBiP₂Se₆ atomic layers, is discovered to achieve a giant NPC effect. Through experimental observations in a Graphene/AgBiP₂Se₆/ Graphene-based vertical photodetector, an irreversible conversion is identified from common PPC photoresponse to atypical NPC photoresponse. Notably, this device demonstrates an exceptionally high negative responsivity (R) of 4.9 × 10⁵ A W⁻¹, surpassing the previous records for NPC photodetectors. Additionally, it exhibits remarkable optoelectronic performances, including an external quantum efficiency of 1.3 × 10⁸% and a detectivity (D) of 3.60 × 10¹² Jones. The exceptionally high NPC photoresponse observed in this device can be attributed to the swift suppression of photogenerated free carriers at robust recombination centers situated at significant depths, induced by the elevated drain-source voltage bias. The remarkably high NPC photoresponse also positions AgBiP₂Se₆ as a promising 2D material for multifunctional optoelectronic devices and an excellent platform for systematic exploration of the NPC effect.

Nature Communications, Published online: 22 January 2024; doi:10.1038/s41467-024-44840-z

Methanol on under-coordinated Pt sites at surface Te vacancies on layered PtTe2 decomposes at a probability >90 % which ultimately produces gaseous molecular hydrogen, methane, water and formaldehyde.

Nature Electronics, Published online: 22 January 2024; doi:10.1038/s41928-024-01120-4

Creating 3D hardware with stacked 2D devices

The key to tuning the carrier character of a Fe/SrTiO₃ interface is the oxidation state of the Fe overlayer. For Fe and FeO, hole bands emerge in the empty bandgap region of STO due to hybridization of Ti- and Fe-derived states across the interface, while for Fe₃O₄ overlayers, a 2D electron system is formed.

Abstract

Oxide electronics provide the key concepts and materials for enhancing silicon-based semiconductor technologies with novel functionalities. However, a basic but key property of semiconductor devices still needs to be unveiled in its oxidic counterparts: the ability to set or even switch between two types of carriers—either negatively (n) charged electrons or positively (p) charged holes. Here, direct evidence for individually emerging n- or p-type 2D band dispersions in STO-based heterostructures is provided using resonant photoelectron spectroscopy. The key to tuning the carrier character is the oxidation state of an adjacent Fe-based interface layer: For Fe and FeO, hole bands emerge in the empty bandgap region of STO due to hybridization of Ti- and Fe- derived states across the interface, while for Fe₃O₄ overlayers, an 2D electron system is formed. Unexpected oxygen vacancy characteristics arise for the hole-type interfaces, which as of yet had been exclusively assigned to the emergence of 2DESs. In general, this finding opens up the possibility to straightforwardly switch the type of conductivity at STO interfaces by the oxidation state of a redox overlayer. This will extend the spectrum of phenomena in oxide electronics, including the realization of combined n/p-type all-oxide transistors or logic gates.