Jing Zhang

A comprehensive review on nanoparticle assembly via the balance of interparticle interactions (e.g., van der Waals, colloidal, capillary, convection, and chemical forces) and nanoparticle-template interactions (e.g., physical confinement, chemical functionalization, additive layer-upon-layer) for broad applications of micropatterned surfaces.

Abstract

Nanoparticles form long-range micropatterns via self-assembly or directed self-assembly with superior mechanical, electrical, optical, magnetic, chemical, and other functional properties for broad applications, such as structural supports, thermal exchangers, optoelectronics, microelectronics, and robotics. The precisely defined particle assembly at the nanoscale with simultaneously scalable patterning at the microscale is indispensable for enabling functionality and improving the performance of devices. This article provides a comprehensive review of nanoparticle assembly formed primarily via the balance of forces at the nanoscale (e.g., van der Waals, colloidal, capillary, convection, and chemical forces) and nanoparticle-template interactions (e.g., physical confinement, chemical functionalization, additive layer-upon-layer). The review commences with a general overview of nanoparticle self-assembly, with the state-of-the-art literature review and motivation. It subsequently reviews the recent progress in nanoparticle assembly without the presence of surface templates. Manufacturing techniques for surface template fabrication and their influence on nanoparticle assembly efficiency and effectiveness are then explored. The primary focus is the spatial organization and orientational preference of nanoparticles on non-templated and pre-templated surfaces in a controlled manner. Moreover, the article discusses broad applications of micropatterned surfaces, encompassing various fields. Finally, the review concludes with a summary of manufacturing methods, their limitations, and future trends in nanoparticle assembly.

This study utilizes ferroelectric engineering to enhance the thermoelectric properties of Bi_0.5Sb_1.5Te₃ (BST) thin films. By adjusting the polarization direction and voltage of the Pb(Zr_0.52Ti_0.48)O₃ (PZT) substrate, the power factor of BST thin films increases by 26.7% to 15.2 µW cm⁻¹ K⁻². This work presents a new approach for enhancing thermoelectric thin films.

Abstract

The Bi_0.5Sb_1.5Te₃ (BST) thin film shows great promise in harvesting low-grade heat energy due to its excellent thermoelectric performance at room temperature. In order to further enhance its thermoelectric performance, specifically the power factor and output power, new approaches are highly desirable beyond the common “composition-structure-performance” paradigm. This study introduces ferroelectric polarization engineering as a novel strategy to achieve these goals. A Pb(Zr_0.52Ti_0.48)O₃/Bi_0.5Sb_1.5Te₃ (PZT/BST) hybrid film is fabricated via magnetron sputtering. Density functional theory calculations demonstrate PZT polarization's influence on charge redistribution and interlayer charge transfer at the PZT/BST interface, facilitating adjustable carrier transport behavior and power factor of the BST film. As a result, a 26.7% enhancement of the power factor, from unpolarized 12.0 to 15.2 µW cm⁻¹ K⁻², is reached by 2 kV out-of-plane downward polarization of PZT. Furthermore, a five-leg generator constructed using this PZT/BST hybrid film exhibits a maximum output power density of 13.06 W m⁻² at ΔT = 39 K, which is 20.8% higher than that of the unpolarized one (10.81 W m⁻²). The research presents a new approach to enhance thermoelectric thin films’ power factor and output performance by introducing ferroelectric polarization engineering.

Nature Communications, Published online: 30 September 2023; doi:10.1038/s41467-023-41874-7

Soft robots made of hydrogels with anisotropic and shape-change properties offer interesting design opportunities. Here, the authors report zwitterionic hydrogels and anisotropic cellulose nanocrystals composites in which the shear-induced alignment of cellulose nanocrystals allows for the development of shape-change programmable miniature robots.

Nature Communications, Published online: 04 October 2023; doi:10.1038/s41467-023-41831-4

The Kagome lattice consists of equilateral triangles occupying each edge of a hexagon, resembling a star with six-fold rotation symmetry. Here, using scanning tunnelling microscopy, Zhang et al observe the breaking of this six-fold rotation symmetry in the Kagome lattice plane of the planar antiferromagnet, FeSn.

Nature Materials, Published online: 28 September 2023; doi:10.1038/s41563-023-01671-5

A route to the rapid and batch production of 12 inch MoS2 monolayers is reported, which shows a synergistic optimization of scale–cost–performance metrics for a transition from lab to fab.

Nature Materials, Published online: 02 October 2023; doi:10.1038/s41563-023-01674-2

Ferroelectric dead layers can form at perovskite interfaces—a major challenge in integrating oxide thin films into devices. Here, by depositing an in-plane-polarized epitaxial buffer layer of Bi5FeTi3O15, out-of-plane polarization is demonstrated in ultrathin films down to the single-unit-cell level.

Nature Electronics, Published online: 28 September 2023; doi:10.1038/s41928-023-01034-7

A reconfigurable field-effect transistor based on a hexagonal boron nitride/rhenium diselenide/hexagonal boron nitride heterostructure can offer nonvolatile control of its channel conductivity via photoinduced trapping of electrons or holes at the bottom dielectric interface.

The advantages of active shell sensitization and the cryogenic field-induced cross relaxation suppression are combined in this study, which significantly promotes the upconversion emission brightness of Er³⁺-rich core–shell nanostructures 1–2 orders of magnitude. Based on the unique property of the material, a temperature-induced high-level information encryption application with QR code is successfully developed.

Abstract

Recent advances reveal that due to the cross-relaxation restriction, impressive upconversion (UC) enhancement (≈100-folds) can be achieved in cryogenic Er³⁺-rich core-inert shell nanostructures (e.g., NaErF₄@NaYF₄), which opens up exciting opportunities in diverse frontier applications. However, further promotion of UC intensity is still highly desired, in which the rational design of nanostructures can play a key role. Herein, it is demonstrated that adopting an active shell design will constantly benefit the UC within a wide temperature range (40–300 K). Specifically, through constructing the luminescent core@active shell@inert shell sandwich nanostructure (e.g., NaErF₄@NaYbF₄@NaYF₄), 8.3–73-folds UC enhancement will be achieved (taking the corresponding core@inert shell structures as competitors). Moreover, from spectral-domain and time-domain spectroscopic experiments, the relevant UC enhancement is convincingly attributed to a temperature-dependent energy injection process (from the active shell to the luminescent core). More interestingly, the unique property of the material makes a temperature-induced high-level encryption application possible, which is obtained by employing the nanomaterials on a quick response (QR) code. These results not only deepen the UC mechanism in multi-layer nanostructures, but also introduce an expanded dimension (via low temperatures) in information security.

A novel approach for generating reflective full-color structural colors with high purity and brightness by utilizing an asymmetric F-P structure based on an ultra-thin bilayer absorber Ni/GSST is proposed. The proposal of applying GSST films to the relevant fields in the visible light band is groundbreaking. These brightly colored devices can cater to various fields such as micro-nano displays.

Abstract

This study proposes a general strategy for constructing an asymmetric Fabry–Perot structure based on an ultra-thin composite absorber, Ni/Ge₂Sb₂Se₄Te₁, to produce reflective full-color structural colors with high brightness and purity. The composite absorber effectively enhances the strong interference effect of thin film, which can significantly reduce the reflection bandwidth of the target band and the reflectivity of the non-target band. Under the premise of optimizing the five-layer base structure, full-color structural colors can be tuned by only changing the thickness of the LaTiO₃ layer. Using the ion-assisted electron beam evaporation technique, a simple and efficient film deposition process, six color devices (namely red, orange, yellow, green, blue, and purple) are successfully prepared with reflection peaks exceeding 90%. The chromaticity coordinates of the proposed high-purity red, green, and blue (RGB) samples are (0.554, 0.339), (0.280, 0.600), and (0.164, 0.075), respectively. These coordinates are fairly close to the standard RGB color coordinates used in liquid crystal displays. This device has a simple structure with a novel material combination and a low production cost, which makes it feasible for mass production using just one coating run process. It has excellent application potential in various fields such as micro-nano displays, anti-counterfeiting measures, reflective color filters, and decorations.

Nonlinear Dispersion Relation and Out-of-Plane Second Harmonic Generation in MoSSe and WSSe Janus Monolayers

In article number 2300958, Marko M. Petrić, Sefaattin Tongay, Giancarlo Soavi, Matteo Barbone, and colleagues investigate second and third harmonic generation in MoSSe and WSSe Janus monolayers. They map the full second-order susceptibility tensor, including out-of-plane components, additionally revealing the nonlinear dispersion near exciton resonances. This sets a bedrock for understanding the nonlinear optical properties of Janus transition metal dichalcogenides and probing their use in the next-generation on-chip multifaceted photonic devices.

In this work, the issue of efficiency loss due to increased cell size for indoor perovskite photovoltaics by developing an in situ pre-nucleation strategy is addressed. A trace amount of β-alaninamide hydrochloride (AHC) is introduced into the perovskite precursor solution, which spontaneously reacts with PbI₂ to form 2D perovskite seed crystals to facilitate 3D perovskite growth.

Abstract

With 40% efficiency under room light intensity, perovskite solar cells (PSCs) will be promising power supplies for low-light applications, particularly for Internet of Things (IoT) devices and indoor electronics, shall they become commercialized. Herein, β-alaninamide hydrochloride (AHC) is utilized to spontaneously form a layer of 2D perovskite nucleation seeds for improved film uniformity, crystallization quality, and solar cell performance. It is found that the AHC addition indeed improves film quality as demonstrated by better uniformity, lower trap density, smaller lattice stress, and, as a result, a 10-fold increase in charge carrier lifetime. Consequently, not only does the small-area (0.09 cm²) PSCs achieve a power conversion efficiency of 42.12%, the large-area cells (1.00 cm², and 2.56 cm²) attain efficiency as high as 40.93%, and 40.07% respectively. All of these are the highest efficiency values for indoor photovoltaic cells with similar sizes, and more importantly, they represent the smallest efficiency loss due to area scale-up. This work provides a new method to fabricate high-performance indoor PSCs (i-PSCs) for IoT devices with great potential in large-area printing technology.

Targeting a scalable and energy-efficient thermal neural network, a novel class of spiking oscillators termed “thermal neuristors” is engineered based on the insulator-to-metal transition (IMT) in vanadium dioxide. Solely through thermal interactions, a wide variety of reconfigurable functionalities mirroring biological neurons are demonstrated, including cascaded information flow, as well as excitatory and inhibitory interactions, without relying on traditional CMOS-based circuits.

Abstract

While the complementary metal-oxide semiconductor (CMOS) technology is the mainstream for the hardware implementation of neural networks, an alternative route is explored based on a new class of spiking oscillators called “thermal neuristors”, which operate and interact solely via thermal processes. Utilizing the insulator-to-metal transition (IMT) in vanadium dioxide, a wide variety of reconfigurable electrical dynamics mirroring biological neurons is demonstrated. Notably, inhibitory functionality is achieved just in a single oxide device, and cascaded information flow is realized exclusively through thermal interactions. To elucidate the underlying mechanisms of the neuristors, a detailed theoretical model is developed, which accurately reflects the experimental results. This study establishes the foundation for scalable and energy-efficient thermal neural networks, fostering progress in brain-inspired computing.

This review highlights three emerging applications of 2D materials in the post-artificial intelligence (AI) era. 2D-based smart fibers demonstrate diverse functionalities, ranging from healthcare monitoring to antipathogenic protection in a wearable manner. Soft robotics addresses the limitations of conventional robotics by introducing 2D-hybridized soft actuators and sensors. Single atom catalysts supported on 2D materials contribute sustainable energy storage and conversion.

Abstract

Recent consecutive discoveries of various 2D materials have triggered significant scientific and technological interests owing to their exceptional material properties, originally stemming from 2D confined geometry. Ever-expanding library of 2D materials can provide ideal solutions to critical challenges facing in current technological trend of the fourth industrial revolution. Moreover, chemical modification of 2D materials to customize their physical/chemical properties can satisfy the broad spectrum of different specific requirements across diverse application areas. This review focuses on three particular emerging application areas of 2D materials: smart fibers, soft robotics, and single atom catalysts (SACs), which hold immense potentials for academic and technological advancements in the post-artificial intelligence (AI) era. Smart fibers showcase unconventional functionalities including healthcare/environmental monitoring, energy storage/harvesting, and antipathogenic protection in the forms of wearable fibers and textiles. Soft robotics aligns with future trend to overcome longstanding limitations of hard-material based mechanics by introducing soft actuators and sensors. SACs are widely useful in energy storage/conversion and environmental management, principally contributing to low carbon footprint for sustainable post-AI era. Significance and unique values of 2D materials in these emerging applications are highlighted, where the research group has devoted research efforts for more than a decade.

Luminescence lifetime sensing suffers from loss of precision and reliability in situations of low signal-to-noise ratio. It is shown how the use of neural networks can overcome this limitation, hence enabling precise and reliable luminescence lifetime nanothermometry in extreme measurement conditions.

Abstract

Luminescence lifetime-based sensing is ideally suited to monitor biological systems due to its minimal invasiveness and remote working principle. Yet, its applicability is limited in conditions of low signal-to-noise ratio (SNR) induced by, e.g., short exposure times and presence of opaque tissues. Herein this limitation is overcome by applying a U-shaped convolutional neural network (U-NET) to improve luminescence lifetime estimation under conditions of extremely low SNR. Specifically, the prowess of the U-NET is showcased in the context of luminescence lifetime thermometry, achieving more precise thermal readouts using Ag₂S nanothermometers. Compared to traditional analysis methods of decay curve fitting and integration, the U-NET can extract average lifetimes more precisely and consistently regardless of the SNR value. The improvement achieved in the sensing performance using the U-NET is demonstrated with two experiments characterized by extreme measurement conditions: thermal monitoring of free-falling droplets, and monitoring of thermal transients in suspended droplets through an opaque medium. These results broaden the applicability of luminescence lifetime-based sensing in fields including in vivo experimentation and microfluidics, while, hopefully, spurring further research on the implementation of machine learning (ML) in luminescence sensing.

A newly developed approach enabling custom-made photoresists suited for additive manufacturing using two-photon lithography is introduced. The approach permits the production of 3D alkaline-earth perovskite (BaZrO₃, CaZrO₃, and SrZrO₃) microarchitectures with sub-micrometer precision. The optical properties of such perovskite architectures are investigated using cathodoluminescence and wide-field photoluminescence emission to understand the defects and determine the photoluminescence lifetimes.

Abstract

3D ceramic architectures are captivating geometrical features with an immense demand in optics. In this work, an additive manufacturing (AM) approach for printing alkaline-earth perovskite 3D microarchitectures is developed. The approach enables custom-made photoresists suited for two-photon lithography, permitting the production of alkaline-earth perovskite (BaZrO₃, CaZrO₃, and SrZrO₃) 3D structures shaped in the form of octet-truss lattices, gyroids, or inspired architectures like sodalite zeolite, and C₆₀ buckyballs with micrometric and nanometric feature sizes. Alkaline-earth perovskite morphological, structural, and chemical characteristics are studied. The optical properties of such perovskite architectures are investigated using cathodoluminescence and wide-field photoluminescence emission to estimate the lifetime rate and defects in BaZrO₃, CaZrO₃, and SrZrO₃. From a broad perspective, this AM methodology facilitates the production of 3D-structured mixed oxides. These findings are the first steps toward dimensionally refined high-refractive-index ceramics for micro-optics and other terrains like (photo/electro)catalysis.

Based on lattice-matched epitaxial growth process, a stepwise seeded growth strategy for precise synthesis of organic bilayer heterostructures with tailored heterojunction surface areas is demonstrated. Furthermore, the relative position and length ratio of component microwires can be finely modulated by controlling the crystallization time of seeded crystals. Notably, these prepared organic heterostructures can be applied in two-dimensional photonic encryption.

Abstract

Organic multilayer heterostructures with accurate spatial organization demonstrate strong light-matter interaction from excitonic responses and efficient carrier transfer across heterojunction interfaces, which are considered as promising candidates toward advanced optoelectronics. However, the precise regulation of the heterojunction surface area for finely adjusting exciton conversion and energy transfer is still formidable. Herein, organic bilayer heterostructures (OBHs) with controlled face-to-face heterojunction via a stepwise seeded growth strategy, which is favorable for efficient exciton propagation and conversion of optical interconnects are designed and synthesized. Notably, the relative position and overlap length ratio of component microwires (L _DSA/L _BPEA = 0.39–1.15) in OBHs are accurately regulated by modulating the crystallization time of seeded crystals, resulting into a tailored heterojunction surface area (R = L _overlap/L _BPEA = 37.6%–65.3%). These as-prepared OBHs present the excitation position-dependent waveguide behaviors for optical outcoupling characteristics with tunable emission colors and intensities, which are applied into two-dimensional (2D) photonic barcodes. This strategy opens a versatile avenue to purposely design OBHs with tailored heterojunctions for efficient energy transfer and exciton conversion, facilitating the application possibilities of advanced integrated optoelectronics.

The crystal polarity has been revealed dependent on the dimension of lamellar crystals. Hence, the altered polarization of P3HT-wrapped MoS₂ upon unveiled adjustable phase interactions with underneath ferroelectric lamellar crystals has been illustrated to significantly decline the binding energy of photo-induced P3HT excitons and enlarge thermodynamic driving forces of electron transition at solid/liquid interfaces, promoting photocatalytic hydrogen evolution reactions therefore.

Abstract

Unveiled as a unique feature of polymer ferroelectric crystals, oriented coalescence within monolayers of poly(vinylidenefluoride-co-trifluoroethylene)(PVDF-TrFE) ferroelectric crystals has been found regulable upon monolayer roughness, which is accompanied by the adjustment of piezoelectric responses, and thus phase polarity. Simply with the deposition of poly(3-hexylthiophene (P3HT)-wrapped molybdenum disulfide (MoS₂) sheets, piezoelectric responses of polymer ferroelectric crystals are surprisingly enhanced further. Also dependent on the degrees of phase polarity, the binding energy of P3HT excitons declines to a level comparable to that of inorganic excitons, together with the alteration of work functions. These results suggest mutual polarization between ferroelectric lamellar crystals and originally nonpolar P3HT-wrapped MoS₂ sheets as a result of dipole-induced dipole phase interactions. As the Fermi levels and driving forces of interfacial electron transition are also adjustable upon involved phase interactions, P3HT-wrapped MoS₂ sheets can photocatalyze hydrogen evolution with an average production rate reaching 4.474 mmol g⁻¹ h⁻¹, which is 1.6 times higher than the results without the aid of phase interactions. Accordingly, amplifying phase interactions has been elucidated feasible, and able to serve as a promising approach to generally promote photocatalytic reactions.

Combining magnetic Kerr microscopy and density functional theory calculations, a successful imaging of antiferromagnetic-ferromagnetic (AFM-FM) phase transition in van der Waals (vdW) AFM CrSBr based on its unique magneto-optic property is demonstrated. These findings reveal enormous prospects for magnetism imaging and control in 2D spintronics with vdW AFM.

Abstract

The advent of van der Waals (vdW) ferromagnetic (FM) and antiferromagnetic (AFM) materials offers unprecedented opportunities for spintronics and magneto-optic devices. Combining magnetic Kerr microscopy and density functional theory calculations, the AFM-FM transition is investigated and a surprising abnormal magneto-optic anisotropy in vdW CrSBr associated with different magnetic phases (FM, AFM, or paramagnetic state) is discovered. This unique magneto-optic property leads to different anisotropic optical reflectivity from different magnetic states, permitting direct imaging of the AFM Néel vector orientation and the dynamic process of the AFM-FM transition within a magnetic field. Using Kerr microscopy, not only the domain nucleation and propagation process is imaged but also the intermediate spin-flop state in the AFM-FM transition is identified. The unique magneto-optic property and clear identification of the dynamics process of the AFM-FM phase transition in CrSBr demonstrate the promise of vdW magnetic materials for future spintronic technology.

A nonvolatile electrical control of the proximity-induced magnetism in SrIrO₃ heterostructures is demonstrated. A giant variation of the anomalous Hall conductivity and Hall angle as function of the applied gate voltage V_g by up to 700% is achieved. The Curie temperature and magnetic anisotropy of the system remain essentially unaffected hinting to gating-induced changes of the anomalous Berry curvature.

Abstract

With its potential for drastically reduced operation power of information processing devices, electric field control of magnetism has generated huge research interest. Recently, novel perspectives offered by the inherently large spin–orbit coupling of 5d transition metals have emerged. Here, nonvolatile electrical control of the proximity-induced magnetism in SrIrO₃ based back-gated heterostructures is demonstrated. Up to a 700% variation of the anomalous Hall conductivity (σ_AHE) and Hall angle (Θ_AHE) as function of the applied gate voltage V _g is reported. In contrast, the Curie temperature T _C ≈ 100 K and magnetic anisotropy of the system remain essentially unaffected by V _g indicating a robust ferromagnetic state in SrIrO₃ which strongly hints to gating-induced changes of the anomalous Berry curvature. The electric-field induced ferroelectric-like state of SrTiO₃ enables nonvolatile switching behavior of σ_AHE and Θ_AHE below 60 K. The large tunability of this system, opens new avenues toward efficient electric-field manipulation of magnetism.

A two-terminal near-infrared (NIR) synaptic device based on multilayer MoSe₂ moiré superlattice can effectively achieve NIR light response and highly parallel sensing and memory functions. The 10 × 10 integrated retinal morphological device array reflects the ability of high-fidelity image under NIR illumination and demonstrates great potential in the field of NIR bionic eye application.

Abstract

Near-infrared (NIR) synaptic devices have attracted great attention in the field of NIR vision sensors due to their highly parallel sensing and memory functions, which emulate the basic biomimetic behaviors of the human visual system. However, it is a great challenge for the 2D material to achieve NIR light response and integration, which obstructs the progress of NIR synaptic devices. Hence, a two-terminal NIR synaptic device based on a multilayer MoSe₂ moiré superlattice is reported. The moiré structure dominated by interlayer excitons significantly enhances the interlayer coupling of multilayer MoSe₂, resulting in a narrower band gap nearly to that of bulk to achieve NIR light response and broadband absorption from 240 nm to 1700 nm. The existence of Se vacancies in MoSe₂ moiré superlattice makes the device show the fundamental synaptic performance. Furthermore, a 10×10 integrated retinal morphologic device array is constructed. Under the 100 s light pulse stimulation of 1060 nm, the pattern obtained after attenuation of 50 s still has a memory level of 14.84%, reflecting the excellent storage function under NIR illumination. This research opens up a new avenue for the realization of NIR artificial retina and bionic eye based on 2D materials.

This work employs a composite material consisting of halide perovskite and organic ferroelectric material to develop a new photoferroelectric synapse, and the photoferroelectricity and some synaptic plasticity are investigated. The classical conditioning in Pavlov's dog experiment can be replicated in the photoferroelectric synapse to realize the learning function of the brain, including memory loss and recovery.

Abstract

Halide perovskite is an emerging material with excellent optoelectronic properties, and also widely used in neuromorphic devices. Recently, halide perovskite has been redefined as exhibiting extraordinary multifunction, e.g., photoferroelectricity. Herein, this work employs a composite material consisting of halide perovskite and organic ferroelectric material to develop a new photoferroelectric synapse, and the photoferroelectricity and some synaptic plasticity are investigated. By the corresponding test analysis, it is demonstrated that photoelectricity and ferroelectricity can reinforce each other in this photoferroelectric composite material. Versatile synaptic behaviors of the nervous system, including paired-pulse facilitation/paired-pulse depression, post-tetanic potentiation /post-tetanic depression, and spiking-rate-dependent plasticity, are successfully simulated. Particularly, the classical conditioning in Pavlov's dog experiment can be replicated in the photoferroelectric synapse to realize the learning function of the brain, including memory loss and recovery. This work could be conducive to the application of multifunctional perovskite materials in synapse devices and neuromorphic computing.

Schematic of the CoFe₂O₄ (CFO) thin film transfer process from Au/CFO/α-MoO₃/STO onto flexible (polyethylene terephthalate) substrate via mechanical exfoliation by breaking weak van der Waals force between MoO₃ sheets. A cross-sectional transmission electron microscopy image of the detached α-MoO₃ on CFO and supporting Au.

Abstract

Integration of functional thin films onto flexible substrates is driven by the need to improve the performance and durability of flexible electronic devices. A van der Waals epitaxy technology that accomplishes the transfer of oxide or metal thin films via exfoliation or dissolution of sacrificial α-MoO₃ layers produced by sputtering is presented. The α-MoO₃ thin films, consisting of weakly bonded 2D layers, grow epitaxially on SrTiO₃ (001) substrates, exhibiting mosaic domains rotated by 90°. Metallic Au films grown on the α-MoO₃ are transferred by mechanical exfoliation or by dissolving the α-MoO₃ in water at 45 °C. Spinel-structured CoFe₂O₄ thin films grown on α-MoO₃ layers are easily transferred to flexible substrates via mechanical exfoliation, and the magnetic anisotropy of the transferred CoFe₂O₄ films is modulated by bending.

Spray-coated liquid metal resistive sensors embedded in an elastomer membrane enable precise detection and computation of object compliance, in the 0.1 to 1 mm N⁻¹ range, compatible with that of biological tissues.

Abstract

Haptic perception of softness is a unique feature of the human skin that relies on the concurrent measurements of the lateral deformation and compression of the skin during object manipulation. This is challenging to implement in robotics because of combined requirements in sensing modalities, skin format, robotic structures, and synthetic materials. A soft sensory skin supporting distributed and bimodal mechanical sensing over large surface area and suitable for robotic hand manipulation is reported. Resistive pressure and strain sensors are prepared with spray-coated liquid metal films embedded in a silicone matrix. Object softness is computed through a calibrated model based on both sensor response curves and the stiffness of the carrier robot. The soft sensory skin enables localization and discrimination of softness that promise interesting future implementation for robotic palpation or precise teleoperation.

Acoustic devices play an increasingly important role in modern society for information technology and intelligent systems. In this review, the recent progress of acoustic devices based on suspended 2D materials and their composites, especially applications in the audio frequency, static pressure, and ultrasonic frequency range, is briefly summarized, emphasizing the advantageous properties of suspended 2D materials and related outstanding device performance.

Abstract

Acoustic devices play an increasingly important role in modern society for information technology and intelligent systems, and recently significant progress has been made in the development of communication, sensing, and energy transduction applications. However, conventional material systems, such as polymers, metals and silicon, show limitations to fulfill the evolving requirements for high-performance acoustic devices of small size, low power consumption, and multifunctional capabilities. 2D materials hold the promise in overcoming the development bottleneck of acoustic devices aforementioned, given their atomic-thin thickness, extensive surface area, superior physical properties, and remarkable layer-stacking tunability. By suspending the 2D materials, mechanical and thermal disruption from substrate will be eliminated, which will enable the development of new classes of acoustic devices with unprecedented sensitivity and accuracy. In this review, the recent progress of acoustic devices based on suspended 2D materials and their composites, especially applications in the audio frequency, static pressure, and ultrasonic frequency range, is briefly summarized, emphasizing the advantageous properties of suspended 2D materials and related outstanding device performance. Together with the development of 2D membrane synthesis, transfer, as well as microelectromechanical fabrication process, suspended 2D materials will shed light on the next-generation high-performance acoustic devices.

In this work, back focal plane (BFP) technique is used to recognize the second harmonic generation (SHG) emission dipole orientation, confirming the in-plane emission dipole of NbOI₂. Furthermore, with increasing hydrostatic pressure, NbOI₂ undergoes a process of increasing, decreasing, and disappearing SHG intensity, corresponding to structural distortion and ferroelectric-paraelectric phase transition, respectively.

Abstract

2D in-plane ferroelectric NbOI₂ exhibits strong second harmonic generation (SHG) and ultrahigh effective susceptibility. To push forward their applications in nonlinear photonics and optoelectronics, it is highly desirable to understand the emission dipole orientation and tunability of SHG, which is not achieved. Here, by integrating tight focusing from parabolic mirror with back focal plane (BFP) imaging technique, for the first time it is demonstrated that SHG emission of NbOI₂ presents purely in-plane dipole orientation in consistent with numerical simulations, suggesting the in-plane components of the SHG susceptibility tensor in NbOI₂ dominate the emission. Moreover, with the aid of ab-initio calculations, it is found that the hydrostatic pressure can dramatically change the structure and resultant SHG intensity of NbOI₂. Explicitly, SHG intensity endures a slight increase due to the distortion of octahedral at low pressure pressure, and then monotonously decreases due to the improvement of structural symmetry with further increasing pressure, and drastically quenching resulting from the ferroelectric to paraelectric phase transition. This work unambiguously demonstrates the dipole emission behavior of SHG and the relationship between structural evolution and SHG intensity, which provides an avenue for tunable nonlinear optics and optoelectronics.

A novel bionic tactile E-skin combining the characteristics of three coupling elements (Stratum spinosum, Meissner corpuscle, and Piezo2 protein) is developed by direct ink writing. Under the coupling enhancement effect, the fabricated E-skin exhibits high sensitivity, low hysteresis, fast response, etc., and it is expanded to a sensor array for the machine learning-assisted intellisense system with brain-like recognition ability.

Abstract

In the pursuit of tactile sensation resembling human skin, the electronic skin (E-skin) has long been a subject of interest and inspires the exploration of various biomimetic structures. Nevertheless, the exceptional functionality of living organisms arises from the synergistic interplay of multiple internal factors, i.e. the coupling enhancement effect, which has received limited attention in existing studies. Here, a tactile E-skin featuring a multicoupled biomimetic structure that mimics three coupling elements found in the skin: Stratum spinosum, Meissner corpuscle, and Piezo2 protein, is proposed. By amalgamating their distinguishing characteristics, this bionic E-skin surpasses the performance of conventional counterparts such as sensitivity as high as 388.5 kPa⁻¹, hysteresis as low as 0.76%, and response times as short as 10 ms. Furthermore, its fabrication methodology of efficient 3D printing shows great advantages in terms of production cost and customization. Finally, the sensor is expanded to a 9 × 9 pixels array for a machine learning-assisted intellisense system to recognize the fruits as a human does, achieving an accuracy of 91.4%. All of these prove the promising potential of this multicoupled biomimetic structure in wearable electronics, human–machine interface, soft robotics, and artificial sensing.

Nature Nanotechnology, Published online: 28 September 2023; doi:10.1038/s41565-023-01513-0

A reagentless, wireless, wearable aptamer nanobiosensor interfaced with a gold nanoparticle-MXene-based electrode enables the selective, automatic and non-invasive analysis of the female hormone oestradiol in sweat during menstrual cycles with subpicomolar sensitivity.

Nature Nanotechnology, Published online: 05 October 2023; doi:10.1038/s41565-023-01520-1

Pentalayer graphene in the rhombohedral stacking order exhibits rich phases including a correlated insulator, isospin-polarized metals and Chern insulators. These findings demonstrate electron-correlated and topological states in crystalline 2D materials without the need for a moiré superlattice.

Nature Nanotechnology, Published online: 05 October 2023; doi:10.1038/s41565-023-01515-y

An integrated transducer based on a planar superconducting resonator coupled to a silicon photonic cavity through a mechanical oscillator made from lithium niobate achieves a transduction efficiency of 0.9%.

Nature Nanotechnology, Published online: 05 October 2023; doi:10.1038/s41565-023-01521-0

Solution-processable CdS ‘bulk’ nanocrystals show efficient on-chip lasing under quasi-continuous-wave conditions with excellent beam quality and pump thresholds.