Jing Zhang

This study demonstrates that rhombohedral layers of binary compounds exhibit polarization saturation beyond a critical stack thickness. The underlying saturation mechanism points to a purely electronic redistribution involving bandgap closure that allows for cross-stack charge transfer and the emergence of free surface charge. The findings, which are of general nature, should be accounted for when designing switching and/or conductive devices based on ferroelectric layered materials.

Abstract

Van der Waals polytypes of broken inversion and mirror symmetries  have been recently shown to exhibit switchable electric polarization even at the ultimate two-layer thin limit. Their out-of-plane polarization has been found to accumulate in a ladder-like fashion with each successive layer, offering 2D building blocks for the bottom-up construction of 3D ferroelectrics. Here, it is demonstrated experimentally that beyond a critical stack thickness, the accumulated polarization in rhombohedral polytypes of molybdenum disulfide saturates. The underlying saturation mechanism, deciphered via density functional theory and self-consistent Poisson–Schrödinger calculations, point to a purely electronic redistribution involving: 1. Polarization-induced bandgap closure that allows for cross-stack charge transfer and the emergence of free surface charge; 2. Reduction of the polarization saturation value, as well as the critical thickness at which it is obtained, by the presence of free carriers. The resilience of polar layered structures to atomic surface reconstruction, which is essentially unavoidable in polar 3D crystals, potentially allows for the design of new devices with mobile surface charges. The findings, which are of general nature, should be accounted for when designing switching and/or conductive devices based on ferroelectric layered materials.

Wireless technologies and wearable sensors provide a distinctive approach to remotely and continuously monitor vital signals without any physical contact. This review aims to provide an overview of the latest advanced wireless technologies utilized in wearable sensors, with a specific focus on emerging functional nanomaterials. The review also introduces system-level integration and representative applications via on-skin and implantable sensing systems.

Abstract

Wireless and wearable sensors attract considerable interest in personalized healthcare by providing a unique approach for remote, noncontact, and continuous monitoring of various health-related signals without interference with daily life. Recent advances in wireless technologies and wearable sensors have promoted practical applications due to their significantly improved characteristics, such as reduction in size and thickness, enhancement in flexibility and stretchability, and improved conformability to the human body. Currently, most researches focus on active materials and structural designs for wearable sensors, with just a few exceptions reflecting on the technologies for wireless data transmission. This review provides a comprehensive overview of the state-of-the-art wireless technologies and related studies on empowering wearable sensors. The emerging functional nanomaterials utilized for designing unique wireless modules are highlighted, which include metals, carbons, and MXenes. Additionally, the review outlines the system-level integration of wireless modules with flexible sensors, spanning from novel design strategies for enhanced conformability to efficient transmitting data wirelessly. Furthermore, the review introduces representative applications for remote and noninvasive monitoring of physiological signals through on-skin and implantable wireless flexible sensing systems. Finally, the challenges, perspectives, and unprecedented opportunities for wireless and wearable sensors are discussed.

The demand for flexible and high-performance devices is increasing with the development of flexible electronics. This study proposes a novel CVD-processable polymer dielectric, Parylene-OH, as a crucial alternative to brittle inorganic dielectrics. Parylene-OH offers a high-quality smooth film with high dielectric constant and photopatternability, positioning it as a promising choice for future flexible devices.

Abstract

The development of flexible and stretchable devices is crucial for realizing future electronics. In particular, for dielectric layer, conventional inorganic materials are limited by their brittle nature, while organic materials suffer from a low dielectric constant. Here, a novel intrinsically photopatternable high-k Parylene-based thin film (Parylene-OH) is fabricated via a chemical vapor deposition process based on the Gorham method, which provides pin-hole free, conformal polymeric film on any type of surface. Parylene-OH can be photo-patterned by UV crosslinking without further lithography processes and dielectric constant of Parylene-OH increases from 6.05 to 7.53 after crosslinking, without degrading other parameters, making it comparable to conventional high-k dielectric, Al₂O₃. Flexible In─Ga─Zn─O (IGZO) thin-film transistors (TFTs) with patterned dielectric layers can withstand higher strain owing to the localized pattern of each unit. A CMOS inverter integrated with n-type IGZO and p-type Te TFTs is successfully fabricated. Parylene-OH can be used in the future of state-of-the-art flexible electronic devices.

Nature Electronics, Published online: 24 April 2024; doi:10.1038/s41928-024-01158-4

A method for integrating polycrystalline molybdenum disulfide using processes in a 200 mm fab facility can create transistors with high robustness and performance comparable with single-crystalline devices.

Nature, Published online: 24 April 2024; doi:10.1038/s41586-024-07306-2

The iconic 6502 microprocessor designed in two key thin-film transistor technologies by independent foundries is used to demonstrate and expand the multi-project wafer approach for flexible electronics.

Nature Photonics, Published online: 24 April 2024; doi:10.1038/s41566-024-01432-z

Holographic waveguides using shallow etching of silicon-on-insulator waveguides makes designing integrated, preset optical vector matrix multiplication computationally tractable and commercially available.

Nature, Published online: 18 April 2024; doi:10.1038/d41586-024-01163-9

Single-atom-thick sheet of gold is probably the first 2D metal. Plus, some bumblebees can survive up to a week underwater and what crackdowns on smoking and vaping will do for public health.

Nature Physics, Published online: 22 April 2024; doi:10.1038/s41567-024-02487-z

Controlling orbital magnetic moments for applications can be difficult. Now local probes of a kagome material, TbV6Sn6, demonstrate how the spin Berry curvature can produce a large orbital Zeeman effect that can be tuned with a magnetic field.

A polymerizable monomer, 4-acryloylmorpholine (ACMO), is introduced into the direct in situ photolithography of perovskite quantum dots, which can act as a solvent to dissolve the perovskite precursor and as a monomer to form a polymer matrix by photo-crosslinking, facilitating the in situ crystallization and growth of PQDs, thus resulting in highly luminescent and uniform perovskite quantum dot patterns.

Abstract

The heavy use of toxic and volatile solvents such as dimethylformamide (DMF) and dimethylsulfoxide (DMSO), in the chemical synthesis of perovskites is known to pose several sustainability challenges that significantly hinder their mass production for commercial applications. Herein, a polymerizable monomer solvent (4-acryloylmorpholine, ACMO) is introduced that permits the growth and optical lithography of perovskite quantum dots (PQDs) through in situ polymerization. Morphological, structural, and optical analyses show that this polymerizable monomer can act both as a solvent to dissolve the perovskite precursor and as a monomer for photopolymerization reactions, allowing direct in situ fabrication and patterning of PQDs. By direct photolithography, colorful PQD patterns with high photoluminescent quantum yields, high resolution (minimum size of 5 µm), and excellent fluorescence uniformity, are successfully demonstrated. The work provides a new sustainable way of in situ patterning PQDs using polymerizable monomer solvents, leading to significant advances in various integrated applications, such as photonic, energy harvesting, and optoelectronic devices.

Nature Nanotechnology, Published online: 19 April 2024; doi:10.1038/s41565-024-01650-0

Plasmonic tunnel junctions integrated with a monolayer semiconductor are found to emit photons with energies exceeding the input electrical potential. This peculiar phenomenon is ascribed to being triggered by inelastic electron tunnelling dipoles inducing optically forbidden transitions in the carrier injection electrode.

ErAs:InGaAlBiAs is a semiconductor nanocomposite that is engineered for a photoconductive switch material that is designed for the detection of THz pulses using telecom wavelength excitation. The band engineering allows a bandgap compatible with a 1550 nm pump while having an effective Fermi level deep in the bandgap to have high dark resistance.

Abstract

Terahertz technology has the potential to have a large impact in myriad fields, such as biomedical science, spectroscopy, and communications. Making these applications practical requires efficient, reliable, and low-cost devices. Photoconductive switches (PCS), devices capable of emitting and detecting terahertz pulses, are a technology that needs more efficiency when working at telecom wavelength excitation (1550 nm) to exploit the advantages this wavelength offers. ErAs:InGaAs is a semiconductor nanocomposite working at this energy; however, high dark resistivity is challenging due to a high electron concentration as the Fermi level lies in the conduction band. To increase dark resistivity, ErAs:InGaAlBiAs material is used as the active material in a PCS detecting Terahertz pulses. ErAs nanoparticles reduce the carrier lifetime to subpicosecond values required for short temporal resolution, while ErAs pins the effective Fermi level in the host material bandgap. Unlike InGaAs, InGaAlBiAs offers enough freedom for band engineering to have a material compatible with a 1550 nm pump and a Fermi level deep in the bandgap, meaning low carrier concentration and high dark resistivity. Band engineering is possible by incorporating aluminum to lift the conduction band edge to the Fermi level and bismuth to keep a bandgap compatible with 1550 nm excitation.

Based on prevalent responsive function of natural creatures, smart actuators based on different functional materials with magnetic/chemical/light/electric-responsive features, including hydrogel, liquid crystal elastomer, dielectric elastomer, shape memory materials, and their composites, are systematically summarized for the application of soft robots, sensors, and grippers.

Abstract

Intelligent actuators have attracted intensive attention due to their broad application scenarios, ranging from precision manufacturing and autonomous robotics to adaptive medical devices. Therein, simplifying structure design and streamlining fabrication processes for responsive materials is crucial for achieving multifunctionality in intelligent actuators. Drawing inspiration from nature, diverse stimuli-responsive materials have been developed, enabling the creation of a broad spectrum of intelligent actuators. Herein, the study aims to provide a systematic overview of smart actuators with different stimuli-responsive materials based on biomimetic strategies. The study commences by describing typical stimulus-response organisms in nature, subsequently categorizing nascent stimuli-responsive materials, and summarizing their respective responsive mechanisms. Potential applications of smart actuators integrated into all-in-one systems are presented for grippers, soft robots, and sensors. Finally, the study ends with an advancement summary together with personal insight into current challenges and future directions.

Electrostatic Nanoparticle Coating

In article 2313299, Doeun Kim, Hyeon-Ho Jeong, and co-authors demonstrate a scalable “one-shot” self-limiting nanoparticle assembly inspired by the underwater adhesion observed in mussels. This technique facilitates the formation of mono-layered nanoparticle assemblies, extending from micro-patterns to covering an entire 2-inch wafer. The authors illustrate this capability through the creation of disordered plasmonic metasurfaces, highlighting their features in full-color painting and charge-sensitive “pick-and-place” nanoparticle patterning.

An information encryption strategy based on the printed total internal reflection structural color and the machine learning algorithm, is developed. This strategy possesses the advantages of low-cost, high precision, high capacity, and dynamic modulation, which is highly promising for a range of applications such as information encryption, data storage, and anti-counterfeiting.

Abstract

Stimuli-responsive structural-color materials have received widespread attention in information encryption due to the significant color changes under different stimuli. However, the trade-off between the capacity of information input, security level, cost, and large-area manufacturing greatly limits the application of structural colors in encryption. Herein, dynamic high-capacity and high-resolution encryption are achieved by implementing printed total internal reflection (TIR) structural color and computer-aided image recognition. The printed TIR microstructures are prepared with relative humidity (RH) responsive polymer, which form a heterogeneous wettability system, and can exhibit vibrant color variation with humidity. As the implemented RH is changed, the printed microstructures will expand or shrink precisely, enabling a full-color modulation across the visible light range. With the color change, each structural-color pixel can be specifically encoded, allowing for this to encrypt dynamic information within the same pattern at different RHs. Furthermore, This study can precisely integrates tremendous different pixels and easily prepare various encrypted patterns, which guarantee the high-capacity information input in a low-cost way. Moreover, through computer programming and algorithm reading, the structural-color patterns can be decoded and decrypted in real-time, thus offering great potential for further encryption, anti-counterfeiting, multiplexing encoding, and data storage.

Strong and anisotropic second- and third-harmonic generation (SHG and THG) processes are observed in a novel 2D material, niobium oxide dibromide (NbOBr₂). Both SHG and THG processes in NbOBr₂ are significantly enhanced up to hundreds of times by coupling with a Fabry-Pérot (F-P) microcavity. The enhancement factor is anisotropic and reaches maximum along the crystal b–axis.

Abstract

2D materials are burgeoning as promising candidates for investigating nonlinear optical effects due to high nonlinear susceptibilities, broadband optical response, and tunable nonlinearity. However, most 2D materials suffer from poor nonlinear conversion efficiencies, resulting from reduced light-matter interactions and lack of phase matching at atomic thicknesses. Herein, a new 2D nonlinear material, niobium oxide dibromide (NbOBr₂) is reported, featuring strong and anisotropic optical nonlinearities with scalable nonlinear intensity. Furthermore, Fabry-Pérot (F-P) microcavities are constructed by coupling NbOBr₂ with air holes in silicon. Remarkable enhancement factors of ≈630 times in second harmonic generation (SHG) and 210 times in third harmonic generation (THG) are achieved on cavity at the resonance wavelength of 1500 nm. Notably, the cavity enhancement effect exhibits strong anisotropic feature tunable with pump wavelength, owing to the robust optical birefringence of NbOBr₂. The ratio of the enhancement factor along the b– and c–axis of NbOBr₂ reaches 2.43 and 5.27 for SHG and THG at 1500 nm pump, respectively, which leads to an extraordinarily high SHG anisotropic ratio of 17.82 and a 10° rotation of THG polarization. The research presents a feasible and practical strategy for developing high-efficiency and low-power-pumped on-chip nonlinear optical devices with tunable anisotropy.

A high-quality room-temperature ferromagnetic material Fe₃GaTe₂ is synthesized by the chemical vapor transport method. An unconventional room-temperature antisymmetric magnetoresistance is observed in 2D Fe₃GaTe₂ devices with the planar symmetry breaking. This work provides new routes to achieve magnetic random storage and logic devices by utilizing the room-temperature thickness-controlled antisymmetric magnetoresistance.

Abstract

Van der Waals (vdW) ferromagnetic materials have emerged as a promising platform for the development of 2D spintronic devices. However, studies to date are restricted to vdW ferromagnetic materials with low Curie temperature (T _c) and small magnetic anisotropy. Here, a chemical vapor transport method is developed to synthesize a high-quality room-temperature ferromagnet, Fe₃GaTe₂ (c-Fe₃GaTe₂), which boasts a high T _c = 356 K and large perpendicular magnetic anisotropy. Due to the planar symmetry breaking, an unconventional room-temperature antisymmetric magnetoresistance (MR) is first observed in c-Fe₃GaTe₂ devices with step features, manifesting as three distinctive states of high, intermediate, and low resistance with the sweeping magnetic field. Moreover, the modulation of the antisymmetric MR is demonstrated by controlling the height of the surface steps. This work provides new routes to achieve magnetic random storage and logic devices by utilizing the room-temperature thickness-controlled antisymmetric MR and further design room-temperature 2D spintronic devices based on the vdW ferromagnet c-Fe₃GaTe₂.

This review explores latest development of leveraging flat-optics to generate ultra-compact quantum light sources with improved efficiency and added functionalities. It highlights photon-pair sources with nonlinear metasurfaces and single-photon emitters in 3D and 2D materials integrated with metasurfaces. The review also discusses current challenges and provide insights into the potential future directions for advancing flat-optics quantum light sources.

Abstract

Quantum light sources are essential building blocks for many quantum technologies, enabling secure communication, powerful computing, and precise sensing and imaging. Recent advancements have witnessed a significant shift toward the utilization of “flat” optics with thickness at subwavelength scales for the development of quantum light sources. This approach offers notable advantages over conventional bulky counterparts, including compactness, scalability, and improved efficiency, along with added functionalities. This review focuses on the recent advances in leveraging flat optics to generate quantum light sources. Specifically, the generation of entangled photon pairs through spontaneous parametric down-conversion in nonlinear metasurfaces, and single photon emission from quantum emitters including quantum dots and color centers in 3D and 2D materials are explored. The review covers theoretical principles, fabrication techniques, and properties of these sources, with particular emphasis on the enhanced generation and engineering of quantum light sources using optical resonances supported by nanostructures. The diverse application range of these sources is discussed and the current challenges and perspectives in the field are highlighted.

Nature Synthesis, Published online: 16 April 2024; doi:10.1038/s44160-024-00518-4

Atomically thin gold nanosheets are predicted to have interesting properties but their synthesis is challenging. Here the exfoliation of two-dimensional single-atom-thick gold, termed goldene, is achieved through wet-chemically etching Ti3C2 from Ti3AuC2. The synthesized goldene has promising properties as a heterocatalyst.

Nature Photonics, Published online: 17 April 2024; doi:10.1038/s41566-024-01423-0

Wide-field mid-infrared photothermal imaging is developed to supress the resolution degradation caused by photo-thermal heat diffusion. By employing a single-objective synthetic-aperture imaging with synchronized subnanosecond mid-infrared and visible light sources, spatial resolution of 120 nm is obtained.

Nature Photonics, Published online: 17 April 2024; doi:10.1038/s41566-024-01422-1

Random-access wide-field mesoscopy enables the imaging of in vivo biodynamics in mice over an area of 160 mm2 and at a subcellular spatial resolution of about 2 μm.

A highly realistic bionic bimodal electronic skin (BB-Skin) is designed via 3d printing and magnetron sputtering methods, which consists of sensing, heating, and tribo-electrode modules. By utilizing the thermal conductivity and electronegativity of materials, it allows for real-time temperature monitoring, contributes to precise artificial intelligent object recognition and enables remote temperature sensing feedback.

Abstract

Skin contacts with objects with different thermal conductivity and tactile perception will produce different temperature and tactile sensations. Here, an innovative creation is presented known as the BB-Skin, a highly realistic bionic bimodal electronic skin, meticulously designed to mirror the thermal sensitivity and tactile perception found in human skin. This technology allows for precise object recognition and offers remote temperature sensing feedback. The BB-Skin comprises temperature sensing, heating, and tribo-electrode modules. Through the utilization of machine learning algorithms that measure the thermal conductivity and electronegativity of materials, a bimodal bionic robot object recognition system is developed, achieving an impressive accuracy rate exceeding 98.11%. The bimodal nature of the system, based on different types of electrical signals that operate independently, significantly enhances the reliability of the device. Moreover, harnessing the inherent capabilities of the BB-Skin, a novel remote temperature sensing and feedback system is successfully implemented. This system adeptly replicates the temperature perception when remotely touching objects and provides users with feedback through gloves embedded with heating and cooling modules.

This work discusses the electrical properties of domains with varying conductance in strained SrMnO₃ thin films, as probed by conducting atomic force microscopy (cAFM) and complemented by scanning electron microscopy. The temporal evolution of the domains is revealed through AFM and X-ray diffraction analysis. The microstructural analysis by transmission electron microscopy provides an understanding of their formation and stabilization.

Abstract

Domains and domain wall engineering have been extensively explored in ferroic materials for a wide range of applications in nanoelectronics and spintronics. Complex oxides exhibiting strongly correlated properties are model platforms for such studies where response to strain or external stimuli such as electric field, temperature and light can be probed. Here, domains in strained SrMnO₃ films, grown on a degenerate semiconductor, allowing for conduction in an out-of-plane geometry, are studied using a combination of microscopy probes. Using conductive atomic force microscopy, electrically isolated domains with varying conductance are found and their temporal evolution is investigated. Further, their formation and microstructure are studied using scanning transmission electron microscopy and secondary electron contrast in scanning electron microscopy. An important contribution is establishing that the observed domains are formed by cracks, driven by inhomogeneous strain relaxation throughout the film, resulting in significantly high strain planes. The potential of secondary electrons to detect domain dependent contrast over a large area, ensuing due to the use of a degenerate semiconductor correlates with the conductive properties of the domains and serves as a new direction to probe domains and domain walls in ferroic materials.

Nature Nanotechnology, Published online: 16 April 2024; doi:10.1038/s41565-024-01645-x

A single-walled carbon nanotube spring stores three times more mechanical energy than a lithium-ion battery, while offering wide temperature stability and posing no explosion risk.