Jing Zhang

Nature, Published online: 22 May 2024; doi:10.1038/s41586-024-07406-z

We develop a low-temperature, damage-free process using van der Waals lamination to integrate multiple circuit tiers into a monolithic three-dimensional device, incorporating unique multi-tier functionality and resolving legacy issues with the layering technology.

This work successfully realizes the tunable full-color ML in BSZLn (50B₂O₃-45SiO₂-5ZnO-0.5Ln₂O₃; Ln = Tb, Tm, Eu) transparent amorphous glass system. The rare earth-doped transparent amorphous glass can produce ML under stress stimulations when in direct contact with polydimethylsiloxane (PDMS) or mixed with PDMS to prepare the ML elastomers. Thanks to the excellent ML performance of the transparent amorphous glass, the detection of automotive brake tribo-force of BSZLn can be achieved.

Abstract

Mechanoluminescence (ML) with the unique mechanical-to-optical energy conversion attracts wide attention for stress sensing. However, the development of ML materials is primarily based on crystalline material due to the crystal structure can provide an appropriate crystal field environment for emission center, which limits the expansion of ML materials and affects the deeper understanding of ML mechanism. Herein, the tunable full-color ML can be achieved in transparent amorphous glass system. The rare earth-doped transparent amorphous glass can produce ML under stress stimulations when in direct contact with polydimethylsiloxane (PDMS) or mixed with PDMS to prepare the ML elastomers. Based on the excellent ML performance of amorphous glass, an advanced device regarding the visualized detection of automotive brake tribo-force has been developed. The findings provide profound insights into the triboelectric potential induced ML phenomenon, which offers the guiding significance in the mechanics-related visualized detection and the design of multi-color ML materials in the future.

A novel flexible synaptic transistor based on MXene floating gates is proposed, which can emulate various synaptic plasticity phenomena. The device exhibits excellent mechanical flexibility and operates at low voltages, enhancing its suitability for wearable applications. It can mimic Pavlovian conditioning under stress and achieve high accuracy in handwritten digit recognition using an FCNN model.

Abstract

Neuromorphic computing, inspired by the functionality of biological neural networks, has emerged as a promising paradigm for artificial intelligence applications, especially in the field of flexible electronics. Among the various artificial synaptic devices, floating-gate synaptic transistors exhibit long-term synaptic plasticity, but they face the challenge of achieving flexible compatibility. In this work, the first demonstration of a flexible MXene floating-gate synaptic transistor is reported, which uses multiple layers of MXene as floating gates and MXene nanosheets as charge state modulators. The device shows excellent mechanical flexibility and can operate at low voltages, which improves its suitability for wearable electronic devices. It can also emulate Pavlovian conditioned reflexes under external stress, suggesting its potential for cognitive learning. Moreover, the device is utilized for handwritten digit recognition by simulating a fully connected neural network, achieving a high recognition accuracy of 92.0%. This demonstrates its practical applicability in neuromorphic computing. Besides, this research achieves the patterning of MXene and its application in flexible floating-gate transistors. It provides a new solution for the integrated fabrication of flexible artificial synaptic devices.

This review summarizes recent advances in graphene field effect transistor (GFET)-based biosensors, focusing on i) fundamental concepts of FETs and the specific electrical properties of GFETs relevant to biosensing; ii) recent schemes to improve the performance of GFET biosensors from several aspects, such as the principle of operation and stability, sensitivity, and specificity; and iii) multi-detection strategies for GFET biosensors.

Abstract

Recently, field-effect transistors (FETs) have emerged as a novel type of multiparameter, high-performance, highly integrated platform for biochemical detection, leveraging their classical three-terminal structure, working principles, and fabrication methods. Notably, graphene materials, known for their exceptional electrical and optical properties as well as biocompatibility, serve as a fundamental component of these devices, further enhancing their advantages in biological detection. This review places special emphasis on recent advancements in graphene field-effect transistor (GFET)-based biosensors and focuses on four main areas: i) the basic concepts of FETs and the specific electrical properties of GFETs; ii) various state-of-the-art approaches to enhance the performance of GFET-based biosensors in terms of operating principles and the “3S”—stability, sensitivity, and specificity; iii) multiplexed detection strategies for GFET-based biosensors; and iv) the current challenges and future perspectives in the field of GFET-based biosensors. It is hoped that this article can profoundly elucidate the development of GFET biosensors and inspire a broader audience.

The double perovskite material of Cs₂NaRECl₆-type, utilizing rare-earth ions as trivalent element, has attracted widespread interest due to its unique optoelectronic properties and wide range of applications. In this article, recent advancements are discussed and challenges in lead-free halide double perovskite compounds. This includes crystal structure, material preparation, optoelectronic performance, various applications, and future research directions.

Abstract

The double perovskite material of Cs₂NaRECl₆-type, utilizing rare-earth (RE) ions as trivalent element, has attracted widespread interest due to its unique optoelectronic properties and wide range of applications. It displays rich optical properties, including visible and infrared light emission through down-shifting, as well as up-conversion emission and radiation-induced emission. These exceptional optical properties make it a promising material for optoelectronic devices such as detectors, light-emitting diodes, lasers and energy storage batteries but also show unique advantages in anti-counterfeiting technology and imaging. In this article, the latest progress is reported and challenges in the crystal structure, material preparation, optoelectronic performance, and various applications of lead-free halide double perovskite (HLDPs) compounds. This is also outline prospective research directions of existing materials, with the aim of facilitating the discovery of new HLDPs materials.

This literature review examines the pivotal roles and applications of autofluorophores—endogenous fluorescent compounds intrinsic to all tissues. The utility of their assessment is explored in non-invasive, label-free clinical assessments for disease detection, surgical guidance, and continuous in vivo tissue characterization, highlighting their significance in biomedical research and clinical practice.

Abstract

Autofluorophores are endogenous fluorescent compounds that naturally occur in the intra and extracellular spaces of all tissues and organs. Most have vital biological functions – like the metabolic cofactors NAD(P)H and FAD⁺, as well as the structural protein collagen. Others are considered to be waste products – like lipofuscin and advanced glycation end products – which accumulate with age and are associated with cellular dysfunction. Due to their natural fluorescence, these materials have great utility for enabling non-invasive, label-free assays with direct ties to biological function. Numerous technologies, with different advantages and drawbacks, are applied to their assessment, including fluorescence lifetime imaging microscopy, hyperspectral microscopy, and flow cytometry. Here, the applications of label-free autofluorophore assessment are reviewed for clinical and health-research applications, with specific attention to biomaterials, disease detection, surgical guidance, treatment monitoring, and tissue assessment – fields that greatly benefit from non-invasive methodologies capable of continuous, in vivo characterization.

Nature Materials, Published online: 22 May 2024; doi:10.1038/s41563-024-01904-1

The authors demonstrate a programmable topological photonic chip with large-scale integration of silicon photonic nanocircuits and microresonators that can be rapidly reprogrammed to implement diverse multifunctionalities.

Copper-coated nanotextured steel is fabricated using electrochemical processes. The combined effects of the nano protrusions on steel and the copper coating exhibit dual anti-bacterial activity for both Gram-negative and Gram-positive. The underlying mechanism involves the generation of reactive oxygen species, induction of oxidative stress, and membrane depolarization depending on whether the nanotexture or the copper dominates the response.

Abstract

Bacterial adhesion to stainless steel, an alloy commonly used in shared settings, numerous medical devices, and food and beverage sectors, can give rise to serious infections, ultimately leading to morbidity, mortality, and significant healthcare expenses. In this study, Cu-coated nanotextured stainless steel (nSS) fabrication have been demonstrated using electrochemical technique and its potential as an antibiotic-free biocidal surface against Gram-positive and negative bacteria. As nanotexture and Cu combine for dual methods of killing, this material should not contribute to drug-resistant bacteria as antibiotic use does. This approach involves applying a Cu coating on nanotextured stainless steel, resulting in an antibacterial activity within 30 min. Comprehensive characterization of the surface revealing that the Cu coating consists of metallic Cu and oxidized states (Cu²⁺ and Cu⁺), has been performed by this study. Cu-coated nSS induces a remarkable reduction of 97% in Gram-negative Escherichia coli and 99% Gram-positive Staphylococcus epidermidis bacteria. This material has potential to be used to create effective, scalable, and sustainable solutions to prevent bacterial infections caused by surface contamination without contributing to antibiotic resistance.

Nature Electronics, Published online: 22 May 2024; doi:10.1038/s41928-024-01167-3

This Review examines the development of van der Waals opto-spintronic devices, highlighting the importance of light–matter interactions in van der Waals magnetic materials and the control of their magnetization via external stimuli, as well as exploring potential opto-spintronic device architectures and applications.

A 4D printed electromagnetic architecture (EMA) with ultra-fast (0.007 s) deformation rates and ultra-sensitive (0.4 Pa) stress detection limits is produced. Further, by integrating the EMA with an MCU and an external power source, a smart trapping device that can sense then response to diverse external stimuli is obtained, which can be used to distinguish and capture aimed objects of a particular mass.

Abstract

4D printing is widely used in soft actuators, flexible electronic devices, and soft robotics. However, existing 4D printed architectures suffer from drawbacks such as long shape-deformation response time or low sensitivity to external stimuli, which greatly limit their applications. To address these shortcomings, 4D printed electromagnetic architectures (EMAs) with both ultra-fast shape-deformation and highly-sensitive detection capabilities have been proposed in this study. The EMA is composed of a 4D printed polymeric scaffold, along with magnetic and conductive parts. Experiments show that the EMA exhibits not only an ultra-fast shape-deformation response time as low as 0.007 s but also a high sensitivity to detect an external pressure down to 0.4 Pa, which is beyond records of all current 4D printing reports. Numerical simulation reveals the rapid shape-deformation and sensing mechanism of EMAs. The effects of cell structures on the performances of EMAs are investigated by parameter optimization. Finally, a “sensing-to-deforming” system has been demonstrated, which can smartly distinguish objects by pressures and then trap or release them by the shape deformation. This work realized the effective coupling of ultra-rapid shape-deformation and ultra-low stress sensing of 4D printed architectures and provided an effective method for integrated development of smart devices in deformation and sensing.

A novel micropatterning technique that harnesses controlled fracture of 2D Ruddlesden–Popper perovskites are developed, enabling precise control over size and shape variations. Pixelated light-emitting diodes (LEDs) are fabricated by using this method, showcasing minimal degradation even as pixel sizes decrease. Additionally, patterning strategies that can be easily adapted for constructing heterostructures and future optoelectronic devices are presented.

Abstract

Quasi-2D Ruddlesden–Popper perovskite (RPP) have surfaced as a promising candidate for light emitting diodes (LEDs) due to its outstanding optoelectronic properties. However, a reliable approach for patterning RPPs remains elusive due to the use of polar solvents in lithographic processes, which can damage the RPP. Here, a reliable and damage-free dry micropatterning method of RPPs is reported, which also offers a cost/time advantage compared to conventional patterning methods. The sharp edges of high aspect ratio silicon micropillars are used to cut RPPs to a pre-defined shape and then the cut RPPs are delaminated to obtain a patterned array of RPPs. The resultant patterned array exhibits no sign of degradation or discernable difference between adjacent pixels, achieving a ≈100% yield. The obtained array is utilized to fabricate a pixelated LED where a sharp electroluminescence (EL) spectrum peaking at 410 nm with full-width-at-half-maximum (FWHM) of 10 nm is observed. The pixelated devices demonstrate the potential to suppress EQE drops as the pixel size decreases, attributed to both the damage-free micropatterning process and the defect tolerance of RPPs. Moreover, further improvements of the patterning method are demonstrated to avoid parasitic emission and suggest a promising strategy to fabricate pixel-accessible micro-LEDs.

A scalable process of black phosphorus-based ink films for multicolored optoelectronic device applications in mid-infrared wavelength. Through the reduction of black phosphorus particle size distribution, the optical bandgap systematically blueshifts, reaching up to 0.8 eV (λ = 1.5 µm). Conversely, alloying black phosphorus with arsenic induces a redshift in the bandgap to 0.28 eV (λ = 4.4 µm).

Abstract

Black phosphorus (bP) based ink with a bulk bandgap of 0.33 eV (λ = 3.7 µm) has recently been shown to be promising for large-area, high performance mid-wave infrared (MWIR) optoelectronics. However, the development of multicolor bP inks expanding across the MWIR wavelength range has been challenging. Here a multicolor ink process based on bP with spectral emission tuned from 0.28 eV (λ = 4.4 µm) to 0.8 eV (λ = 1.5 µm) is demonstrated. Specifically, through the reduction of bP particle size distribution (i.e., lateral dimension and thickness), the optical bandgap systematically blueshifts, reaching up to 0.8 eV. Conversely, alloying bP with arsenic (bP_{1− x} As _x ) induces a redshift in the bandgap to 0.28 eV. The ink processed films are passivated with an infrared-transparent epoxy for stable infrared emission in ambient air. Utilizing these multicolor bP-based inks as an infrared light source, a gas sensing system is demonstrated that selectively detects gases, such as CO₂ and CH₄ whose absorption band varies around 4.3 and 3.3 µm, respectively. The presented ink formulation sets the stage for the advancement of multiplex MWIR optoelectronics, including spectrometers and spectral imaging using a low-cost material processing platform.

Exploring the mechanical degree of freedom, we demonstrates pressure sensors based on 2D non-layered material β-In₂S₃. These devices exhibit remarkable features including broad range, high linearity, and fast response, facilitating efficient sensing over a wide pressure range. Furthermore, we establish the frequency scaling law for β-In₂S₃ nanomechanical resonators, which can enable future wafer-scale design and production of integrated sensors.

Abstract

Two-dimensional (2D) non-layered materials, along with their unique surface properties, offer intriguing prospects for sensing applications. Introducing mechanical degrees of freedom is expected to enrich the sensing performances of 2D non-layered devices, such as high frequency, high tunability, and large dynamic range, which could lead to new types of high performance nanosensors. Here, we demonstrate 2D non-layered nanomechanical resonant sensors based on β-In₂S₃, where the devices exhibit robust nanomechanical vibrations up to the very high frequency (VHF) band. We show that such device can operate as pressure sensor with broad range (from 10⁻³ Torr to atmospheric pressure), high linearity (with a nonlinearity factor as low as 0.0071), and fast response (with an intrinsic response time less than 1 μs). We further unveil the frequency scaling law in these β-In₂S₃ nanomechanical sensors and successfully extract both the Young's modulus and pretension for the crystal. Our work paves the way towards future wafer-scale design and integrated sensors based on 2D non-layered materials.

This work presents a zero-voltage-writing artificial nervous system (ZANS) that integrates a bio-source-sensing device (BSSD) for ion-based sensing and power generation with a hafnium-zirconium oxide-ferroelectric tunnel junction (HZO-FTJ) for the continuously adjustable resistance state. Moreover, by connecting it to the sciatic nerve of the rabbit's leg, precise control of the rabbit's leg muscles with zero-voltage-writing capability is successfully realized.

Abstract

The artificial nervous system proves the great potential for the emulation of complex neural signal transduction. However, a more bionic system design for bio-signal transduction still lags behind that of physical signals, and relies on additional external sources. Here, this work presents a zero-voltage-writing artificial nervous system (ZANS) that integrates a bio-source-sensing device (BSSD) for ion-based sensing and power generation with a hafnium-zirconium oxide-ferroelectric tunnel junction (HZO-FTJ) for the continuously adjustable resistance state. The BSSD can use ion bio-source as both perception and energy source, and then output voltage signals varied with the change of ion concentrations to the HZO-FTJ, which completes the zero-voltage-writing neuromorphic bio-signal modulation. In view of in/ex vivo biocompatibility, this work shows the precise muscle control of a rabbit leg by integrating the ZANS with a flexible nerve stimulation electrode. The independence on external source enhances the application potential of ZANS in robotics and prosthetics.

Nature Chemistry, Published online: 17 May 2024; doi:10.1038/s41557-024-01525-w

Liquid droplets form in cells to concentrate specific biomolecules (while excluding others) in order to perform specific functions. The molecular mechanisms that determine whether different macromolecules undergo co-partitioning or exclusion has so far remained elusive. Now, two studies uncover key principles underlying this selectivity.

Silicon-based avalanche photodetectors (APDs) have emerged as crucial devices in imaging and optical communication systems. For challenges such as silicon bandgap, high operating voltage, and large noise, an innovative approach to fabricate highly sensitive multilayer graphene/epitaxial silicon near-infrared (NIR) APDs is introduced. This study also offers the opportunity to develop CMOS-compatible room temperature NIR image sensors and signal receivers.

Abstract

2D materials and their heterostructures exhibit considerable potential in the development of avalanche photodetectors (APDs) with high gain, response, and signal-to-noise ratio. These materials hold promise in addressing inherent technical challenges associated with APDs, such as low light absorption coefficient, elevated noise current, and substantial power consumption due to high bias resulting in only moderate current gain. In this work, a macro-assembled graphene nanofilm (nMAG)/epitaxial silicon (epi-Si) vertical heterostructure photodetector with a responsivity of 0.38 A W⁻¹ and a response time of 1.4 µs is reported. The photodetectors use high-quality nMAG as the absorption layer and a lightly-doped epi-Si layer as the multiplication region under the avalanche mode to provide a high responsivity (2.51 mA W⁻¹) and detectivity (2.67 × 10⁹ Jones) at 1550 nm, which can achieve high-resolution imaging. In addition, the APD displays a weak noise level and an avalanche gain of M = 1123. It can work with relatively low avalanche turn-on voltages and achieve self-quenching by switching from illumination to dark during avalanche multiplication, with a real-time data transfer rate of 38 Mbps in near-infrared light communication data links. The proposed structure enables the fabrication of high-performance APDs in the infrared range using complementary-metal-oxide-semiconductor (CMOS)-compatible processes.

This article presents the distinct thickness-related properties of boron nitride nanosheets (BNNSs), encompassing Raman signatures, unique adsorption behavior, mechanical properties, thermal conductivity, and thermal expansion coefficients. It delves into the mechanisms governing thickness effects and explores BNNS applications in surface-enhanced Raman spectroscopy, metal-enhanced fluorescence, and thermal management.

Abstract

Owing to its exceptional properties and wide-ranging potential applications from aerospace to medicine, hexagonal boron nitride (h-BN) has garnered considerable attention over the past decades. Boron nitride nanosheets (BNNSs), atomically thin h-BN, not only inherit most of the outstanding properties of h-BN but also exhibit superior characteristics compared to their bulk counterpart due to their reduced thickness, such as special adsorption behaviors and enhanced thermal conductivity. Furthermore, BNNSs display distinct thickness-dependent properties from graphene and other 2D materials, such as unique mechanical response under indentation. This feature article provides an overview of the thickness-related special properties of BNNSs, primarily derived from mechanically exfoliated h-BN single crystals. These properties span various domains, including Raman signatures, molecule adsorption-induced conformational changes, mechanical properties, thermal conductivity, and thermal expansion coefficients. Moreover, the feature article explores the underlying mechanisms governing these atomic-scale thickness effects. Leveraging their unique properties, the feature article investigates diverse applications of BNNSs, encompassing surface-enhanced Raman spectroscopy, metal-enhanced fluorescence, and isotropic thermal management.

Deterministic integration of phase-pure 2D perovskite nanosheets leads to novel dual-peak emission phenomenon and dual-band photoresponse characteristic modulated by comprising quantum wells. By combining the modulated dual-band photoresponse with the double-beam irradiation mode and the encryption algorithm, secure light communication system is constructed to explore the potential of heterostructure-based PDs in advanced functional optoelectronic fields.

Abstract

Deterministic integration of phase-pure Ruddlesden–Popper (RP) perovskites has great significance for realizing functional optoelectronic devices. However, precise fabrications of artificial perovskite heterostructures with pristine interfaces and rational design over electronic structure configurations remain a challenge. Here, the controllable synthesis of large-area ultrathin single-crystalline RP perovskite nanosheets and the deterministic fabrication of arbitrary 2D vertical perovskite heterostructures are reported. The 2D heterostructures exhibit intriguing dual-peak emission phenomenon and dual-band photoresponse characteristic. Importantly, the interlayer energy transfer behaviors from wide-bandgap component to narrow-bandgap component modulated by comprising quantum wells are thoroughly revealed. Functional nanoscale photodetectors are further constructed based on the 2D heterostructures. Moreover, by combining the modulated dual-band photoresponse characteristic with double-beam irradiation modes, and introducing an encryption algorithm mechanism, a light communication system with high security and reliability is achieved. This work can greatly promote the development of heterogeneous integration technologies of 2D perovskites, and could provide a competitive candidate for advanced integrated optoelectronics.

This review highlights the recent developments in electronic skin (e-skin) caused by various new materials and functions. The topics covered include material properties, functional integration, and applications. The current application status and future development directions and challenges of e-skin in the field of health monitoring are discussed.

Abstract

Electronic skin (e-skin), a skin-like wearable electronic device, holds great promise in the fields of telemedicine and personalized healthcare because of its good flexibility, biocompatibility, skin conformability, and sensing performance. E-skin can monitor various health indicators of the human body in real time and over the long term, including physical indicators (exercise, respiration, blood pressure, etc.) and chemical indicators (saliva, sweat, urine, etc.). In recent years, the development of various materials, analysis, and manufacturing technologies has promoted significant development of e-skin, laying the foundation for the application of next-generation wearable medical technologies and devices. Herein, the properties required for e-skin health monitoring devices to achieve long-term and precise monitoring and summarize several detectable indicators in the health monitoring field are discussed. Subsequently, the applications of integrated e-skin health monitoring systems are reviewed. Finally, current challenges and future development directions in this field are discussed. This review is expected to generate great interest and inspiration for the development and improvement of e-skin and health monitoring systems.

Nature Nanotechnology, Published online: 17 May 2024; doi:10.1038/s41565-024-01664-8

A single monolayer semiconductor integrated into a plasmonic tunnel junction exhibits electroluminescence with photon energies that exceed the excitation electron potential. This phenomenon is shown to be indirectly triggered by inelastically tunnelling electrons.

In this review, it is described how methods from materials science are being used to understand and control the behavior of biological cells in elastic and structured environments. This field currently moves from single cells to cell collectives and organoids, and from 2D to 3D environments. Special emphasis is placed on the role of mathematical modeling.

Abstract

With the advent of mechanobiology, cell shape and forces have emerged as essential elements of cell behavior and fate, in addition to biochemical factors such as growth factors. Cell shape and forces are intrinsically linked to the physical properties of the environment. Extracellular stiffness guides migration of single cells and collectives as well as differentiation and developmental processes. In confined environments, cell division patterns are altered, cell death or extrusion might be initiated, and other modes of cell migration become possible. Tools from materials science such as adhesive micropatterning of soft elastic substrates or direct laser writing of 3D scaffolds have been established to control and quantify cell shape and forces in structured environments. Herein, a review is given on recent experimental and modeling advances in this field, which currently moves from single cells to cell collectives and tissue. A very exciting avenue is the combination of organoids with structured environments, because this will allow one to achieve organotypic function in a controlled setting well suited for long-term and high-throughput culture.

Mechanical Metamaterials

In article number 2301133, Martin Wegener, Martin Bastmeyer, Motomu Tanaka, and co-workers design and manufacture microstructured bio-metamaterials based on an elastic photoresist and two-photon laser printing. The differential responses of human mesenchymal stem cells, both on the cellular level and the sub-cellular level, correlate with the calculated effective elastic properties of the bio-metamaterials, suggesting the potential of bio-metamaterials towards mechanical regulation of cells by the arrangement of unit cells.

Mesenchymal stem cells experience and respond to the effective elastic properties of three types of metamaterials made from an elastomer-like photoresist manufactured by two-photon laser printing both on the cellular and the subcellular level. These findings suggest the potential of “bio-metamaterials” toward mechanical regulation of cell behavior by the design of unit cells without changing the base material.

Abstract

Cell behaviors significantly depend on the elastic properties of the microenvironments, which are distinct from commonly used polymer-based substrates. Artificial elastic materials called metamaterials offer large freedom to adjust their effective elastic properties as experienced by cells, provided (i) the metamaterial unit cell is sufficiently small compared to the biological cell size and (ii) the metamaterial is sufficiently soft to deform by the active cell contraction. Thus, metamaterials targeting bio-applications (bio-metamaterials) appear as a promising path toward the mechanical control of stem cells. Herein, human mesenchymal stem cells (hMSCs) are cultured on three different types of planar periodic elastic metamaterials. To fulfill the above two key requirements, microstructured bio-metamaterials have been designed and manufactured based on a silicon elastomer-like photoresist and two-photon laser printing. In addition to the conventional morphometric and immunocytochemical analysis, the traction force that hMSCs exert on metamaterials are inferred by converting the measured displacement-vector fields into force-vector fields. The differential responses of hMSCs, both on the cellular level and the sub-cellular level, correlate with the calculated effective elastic properties of the bio-metamaterials, suggesting the potential of bio-metamaterials toward mechanical regulation of cell behaviors by the arrangement of unit cells.

Large-area continuous thin films of metastable trigonal Cr₂S₃ are grown by ultralow gas-flow governed dynamic transport methods. The anisotropic SHG response of as-prepared Cr₂S₃ demonstrated effective second-order nonlinearity of 48.0 pm V⁻¹, in which sulfur vacancies and dangling bonds could break the surface central-symmetry and contribute nonlinear optical polarizabilities, providing a new understanding of SHG for nonlayered 2D materials.

Abstract

As for nonlayered 2D polymorphic materials, especially for Cr-based chalcogenides, large-area thin film growth with phase control is considered the most important synthesis challenge for magnetic, electronic, and optoelectronic devices. However, the synthesis methods of large continuous thin films for nonlayered 2D materials are still limited and rarely reported, also for the phase control growth, which is inhibited by isotropic 3D growth and similar Gibbs free energy for different phases. Herein, enhanced mass transport chemical vapor deposition is established to achieve the control synthesis of trigonal Cr₂S₃ thin films, in which the stable boundary layer supplies the continuous reaction species and tunes the reaction kinetics. The trigonal phase formation is confirmed by atomic structure characterization, optical absorption and piezoelectric measurements, demonstrating unique physical properties different from rhombohedral phase. The trigonal Cr₂S₃ thin films show obvious layer independent and dissimilar angle-resolved harmonic generation, indicating the surface broken symmetry that can be understood by the combination of negligible piezoelectric response for bulk. The work presents the large-area synthesized strategy by the modification of mass transport for nonlayered 2D materials with new phase formation and establishes the surface symmetry breaking dominated SHG mechanism for future nonlinear optical materials.

Electrochemical analysis is a highly sensitive, cost-effective, and rapidly advancing technique with broad applicability. Its integration with diverse signal modes like light, magnetic, and thermal offers biosensors with enhanced capabilities. By combining multi-modes/signals, detection accuracy improves dramatically, reducing false positives or negatives.

Abstract

Electrochemical (EC) analysis has emerged as a high-sensitivity, reliable, cost-effective, and rapidly evolving technique that has garnered significant attention across diverse domains. Furthermore, EC-based techniques hold great potential for miniaturization and integration. The integration of EC techniques with diverse mode/signal (such as light, magnetic, and thermal signals, etc.) provides unique opportunities for biosensors to acquire more information through a single sensing platform. By coupling multiple signals or processing them logically, the detection accuracy can be further improved, and the probability of false positives or negatives can be minimized. In this review, a thorough analysis of multi- mode/signal sensors in the field of EC sensing is conducted, along with their integration with various sensing techniques (e.g., fluorescence, photothermal, colorimetry, microfluidic, etc.). The aim is to delve into the latest advances, potential applications, as well as challenges in multi-mode/signal biosensors, where the utilization of multiple sensing modalities helps enhance accuracy, sensitivity, and selectivity. This review provides new insight into the synergistic effects of integrating EC sensing with other techniques, aiming to shed light on the near-future developments in EC-integrated multi-mode/signal biosensors.

2D Janus TMDs have garnered significant attention for their quantum properties, stemming from their unique asymmetric structure. This work identifies the most stable point defects in Janus WSeS${\mathrm{W}}_{{\mathrm{Se}}}^{\mathrm{S}}$ using HR-STEM, DFT, and PL spectroscopy, and establishes their impact on structural and optical properties. The findings introduce a defect genome for Janus TMDs, providing essential guidelines for assessing their structural quality and device functionality.

Abstract

2D Janus Transition Metal Dichalcogenides (TMDs) have attracted much interest due to their exciting quantum properties arising from their unique two-faced structure, broken-mirror symmetry, and consequent colossal polarization field within the monolayer. While efforts are made to achieve high-quality Janus monolayers, the existing methods rely on highly energetic processes that introduce unwanted grain-boundary and point defects with still unexplored effects on the material's structural and excitonic properties Through high-resolution scanning transmission electron microscopy (HRSTEM), density functional theory (DFT), and optical spectroscopy measurements; this work introduces the most encountered and energetically stable point defects. It establishes their impact on the material's optical properties. HRSTEM studies show that the most energetically stable point defects are single (V _S and V _Se) and double chalcogen vacancy (V _S −V _Se), interstitial defects (M_i), and metal impurities (M_W) and establish their structural characteristics. DFT further establishes their formation energies and related localized bands within the forbidden band. Cryogenic excitonic studies on h-BN-encapsulated Janus monolayers offer a clear correlation between these structural defects and observed emission features, which closely align with the results of the theory. The overall results introduce the defect genome of Janus TMDs as an essential guideline for assessing their structural quality and device properties.

2D polarization materials are promising for miniaturized devices due to their unique properties. However, strategies for creating 2D polarization through new mechanisms are rare. This work introduces a 2D Janus structure with both vertical and planar polarization, achieved by applying force with a nanoprobe. This technique breaks symmetry at the atomic level, inducing polarization and paving the way for new 2D polarization materials' development and design.

Abstract

2D polarization materials have emerged as promising candidates for meeting the demands of device miniaturization, attributed to their unique electronic configurations and transport characteristics. Although the existing inherent and sliding mechanisms are increasingly investigated in recent years, strategies for inducing 2D polarization with innovative mechanisms remain rare. This study introduces a novel 2D Janus state by modulating the puckered structure. Combining scanning probe microscopy, transmission electron microscopy, and density functional theory calculations, this work realizes force-triggered out-of-plane and in-plane dipoles with distorted smaller warping in GeSe. The Janus state is preserved after removing the external mechanical perturbation, which could be switched by modulating the sliding direction. This work offers a versatile method to break the space inversion symmetry in a 2D system to trigger polarization in the atomic scale, which may open an innovative insight into configuring novel 2D polarization materials.

Nature Nanotechnology, Published online: 15 May 2024; doi:10.1038/s41565-024-01672-8

FRETfluors—nanostructures with Cy3 and Cy5 dyes and a DNA scaffold—are used to generate distinct spectroscopic signals from different configurations and mixtures of mRNA, dsDNA and proteins in an anti-Brownian electrokinetic trap for single-molecule multiplexed sensing.