Jing Zhang

Nature Materials, Published online: 23 June 2022; doi:10.1038/s41563-022-01291-5

A competitive-chemical-reaction-based growth mechanism by controlling the kinetic parameters can easily realize the growth of transition metal chalcogenides and transition metal phosphorous chalcogenides with different compositions and phases.

Nature Materials, Published online: 23 June 2022; doi:10.1038/s41563-022-01301-6

A general method by controlling reaction kinetics is proposed to synthesize 67 kinds of two-dimensional crystal with custom-made phases and compositions, in particular, Fe- and Cr-based (layered and non-layered) chalcogenides and phosphorous chalcogenides, which show interesting ferromagnetism and superconductivity properties.

Nature, Published online: 22 June 2022; doi:10.1038/s41586-022-04768-0

Developments, challenges and opportunities in using two-dimensional materials for the next generation of non-volatile spin-based memory technologies are reviewed, and possible disruptive improvements are discussed.

Small-scale soft robots have immense potential at present and in the foreseeable future, with utility in exploration, medical, and biomimetic applications, among others. Being enabling technologies, the fabrication and integration techniques of small-scale soft robots are systematically reviewed. By discussing the challenges and opportunities, potential directions for the further development of small-scale soft robots are highlighted.

Abstract

Small-scale soft robots are attracting increasing interest for visible and potential applications owing to their safety and tolerance resulting from their intrinsic soft bodies or compliant structures. However, it is not sufficient that the soft bodies merely provide support or system protection. More importantly, to meet the increasing demands of controllable operation and real-time feedback in unstructured/complicated scenarios, these robots are required to perform simplex and multimodal functionalities for sensing, communicating, and interacting with external environments during large or dynamic deformation with the risk of mismatch or delamination. Challenges are encountered during fabrication and integration, including the selection and fabrication of composite/materials and structures, integration of active/passive functional modules with robust interfaces, particularly with highly deformable soft/stretchable bodies. Here, methods and strategies of fabricating structural soft bodies and integrating them with functional modules for developing small-scale soft robots are investigated. Utilizing templating, 3D printing, transfer printing, and swelling, small-scale soft robots can be endowed with several perceptual capabilities corresponding to diverse stimulus, such as light, heat, magnetism, and force. The integration of sensing and functionalities effectively enhances the agility, adaptability, and universality of soft robots when applied in various fields, including smart manufacturing, medical surgery, biomimetics, and other interdisciplinary sciences.

A zwitterion formamidine sulfinic acid (FSA) is deposited at the tin(IV) oxide (SnO₂)/perovskite interface to induce the crystallization of high-quality black-phase formamidinium lead iodide (FAPbI₃), and also help reduce the side effect of the residual lead iodide (PbI₂), yielding an impressive power conversion efficiency (PCE) of 24.1% and 1000 h long-term operational stability.

Abstract

Black-phase formamidinium lead iodide (FAPbI₃) with narrow bandgap and high thermal stability has emerged as the most promising candidate for highly efficient and stable perovskite photovoltaics. In order to overcome the intrinsic difficulty of black-phase crystallization and to eliminate the lead iodide (PbI₂) residue, most sequential deposition methods of FAPbI₃-based perovskite will introduce external ions like methylammonium (MA⁺), cesium (Cs⁺), and bromide (Br^–) ions to the perovskite structure. Here a zwitterion-functionalized tin(IV) oxide (SnO₂) is introduced as the electron-transport layer (ETL) to induce the crystallization of high-quality black-phase FAPbI₃. The SnO₂ ETL treated with the zwitterion of formamidine sulfinic acid (FSA) can help rearrange the stack direction, orientation, and distribution of residual PbI₂ in the perovskite layer, which reduces the side effect of the residual PbI₂. Besides, the FSA functionalization also modifies SnO₂ ETL to suppress deep-level defects at the perovskite/SnO₂ interface. As a result, the FSA–FAPbI₃-based perovskite solar cells (PSCs) exhibit an excellent power conversion efficiency of up to 24.1% with 1000 h long-term operational stability. These findings provide a new interface engineering strategy on the sequential fabrication of black-phase FAPbI₃ PSCs with improved optoelectronic performance.

Quantum Dots

In article 2103907, Kuan Eng Johnson Goh and co-workers report electrostatically defined quantum dots in bilayer WS₂ grown by chemical vapor deposition and capped by HfO₂ dielectric using atomic layer deposition. This marks a key milestone in scalable approaches toward 2D-semiconductor-based quantum devices, which had hitherto only been demonstrated with micrometer-sized exfoliated flakes.

This review introduces novel synthetic strategies to produce large-area single crystal thin films of various materials and discusses the technological challenges of dealing with the isostructured crystals (3D materials such as metals, III-V semiconductors, oxide perovskites, halide perovskites, organic semiconductors) and anisotropic crystals (2D materials such as graphene, hBN, and metal chalcogenides).

Abstract

Wafer-scale growth of single crystal thin films of metals, semiconductors, and insulators is crucial for manufacturing high-performance electronic and optical devices, but still challenging from both scientific and industrial perspectives. Recently, unconventional advanced synthetic approaches have been attempted and have made remarkable progress in diversifying the species of producible single crystal thin films. This review introduces several new synthetic approaches to produce large-area single crystal thin films of various materials according to the concepts and principles.

Hexagonal boron nitride (h-BN) has attracted great interest motivated by fascinating properties in the fields of quantum optics, electronics, and optoelectronics. The most recent discoveries of structural, optical, and electrical properties of h-BN and advancements in emerging photonic and electronic applications are reviewed.

Abstract

Hexagonal boron nitride (h-BN), an insulating 2D layered material, has recently attracted tremendous interest motivated by the extraordinary properties it shows across the fields of optoelectronics, quantum optics, and electronics, being exotic material platforms for various applications. At an early stage of h-BN research, it is explored as an ideal substrate and insulating layers for other 2D materials due to its atomically flat surface that is free of dangling bonds and charged impurities, and its high thermal conductivity. Recent discoveries of structural and optical properties of h-BN have expanded potential applications into emerging electronics and photonics fields. h-BN shows a very efficient deep-ultraviolet band-edge emission despite its indirect-bandgap nature, as well as stable room-temperature single-photon emission over a wide wavelength range, showing a great potential for next-generation photonics. In addition, h-BN is extensively being adopted as active media for low-energy electronics, including nonvolatile resistive switching memory, radio-frequency devices, and low-dielectric-constant materials for next-generation electronics.

Computers inspired by the brain offer the exciting prospect of energy efficiency. Complex oxides can serve as building blocks for brain-inspired computing owing to their adaptive electronic structure and high sensitivity to environmental stimuli.

Abstract

The fields of brain-inspired computing, robotics, and, more broadly, artificial intelligence (AI) seek to implement knowledge gleaned from the natural world into human-designed electronics and machines. In this review, the opportunities presented by complex oxides, a class of electronic ceramic materials whose properties can be elegantly tuned by doping, electron interactions, and a variety of external stimuli near room temperature, are discussed. The review begins with a discussion of natural intelligence at the elementary level in the nervous system, followed by collective intelligence and learning at the animal colony level mediated by social interactions. An important aspect highlighted is the vast spatial and temporal scales involved in learning and memory. The focus then turns to collective phenomena, such as metal-to-insulator transitions (MITs), ferroelectricity, and related examples, to highlight recent demonstrations of artificial neurons, synapses, and circuits and their learning. First-principles theoretical treatments of the electronic structure, and in situ synchrotron spectroscopy of operating devices are then discussed. The implementation of the experimental characteristics into neural networks and algorithm design is then revewed. Finally, outstanding materials challenges that require a microscopic understanding of the physical mechanisms, which will be essential for advancing the frontiers of neuromorphic computing, are highlighted.

A pass-transistor logic configuration based on pseudo-NMOS is realized on a 4-inch high-quality monolayer MoS₂ wafer. Such preliminary integration efforts exhibit a promising future for 2D semiconductors in integrated circuit application.

Abstract

2D semiconductors, such as molybdenum disulfide (MoS₂), have attracted tremendous attention in constructing advanced monolithic integrated circuits (ICs) for future flexible and energy-efficient electronics. However, the development of large-scale ICs based on 2D materials is still in its early stage, mainly due to the non-uniformity of the individual devices and little investigation of device and circuit-level optimization. Herein, a 4-inch high-quality monolayer MoS₂ film is successfully synthesized, which is then used to fabricate top-gated (TG) MoS₂ field-effect transistors with wafer-scale uniformity. Some basic circuits such as static random access memory and ring oscillators are examined. A pass-transistor logic configuration based on pseudo-NMOS is then employed to design more complex MoS₂ logic circuits, which are successfully fabricated with proper logic functions tested. These preliminary integration efforts show the promising potential of wafer-scale 2D semiconductors for application in complex ICs.

The magneto–electric–optical coupling is realized in multiferroic BiFeO₃-based films at room temperature by engineering ferroelastic switching. The reversible ferroelastic switching is ubiquitous in BiFeO₃-based films with flexible strain states and domain patterns, which is determined by the photoinduced electric field and symmetry mismatch in films. This work provides a framework for multi-field-driven magnetoelectric memories with low power consumption.

Abstract

Manipulating ferroic orders and realizing their coupling in multiferroics at room temperature are promising for designing future multifunctional devices. Single external stimulation has been extensively proved to demonstrate the ability of ferroelastic switching in multiferroic oxides, which is crucial to bridge the ferroelectricity and magnetism. However, it is still challenging to directly realize multi-field-driven magnetoelectric coupling in multiferroic oxides as potential multifunctional electrical devices. Here, novel magneto–electric–optical coupling in multiferroic BiFeO₃-based thin films at room temperature mediated by deterministic ferroelastic switching using piezoresponse/magnetic force microscopy and aberration-corrected transmission electron microscopy are shown. Reversible photoinduced ferroelastic switching exhibiting magnetoelectric responses is confirmed in BiFeO₃-based films, which works at flexible strain states. This work directly demonstrates room-temperature magneto–electric–optical coupling in multiferroic films, which provides a framework for designing potential multi-field-driven magnetoelectric devices such as energy conservation memories.

Nature Nanotechnology, Published online: 20 June 2022; doi:10.1038/s41565-022-01145-w

Self-adhesive bioimpedance graphene electronic tattoos enable accurate continuous blood pressure monitoring.

Nature Electronics, Published online: 16 June 2022; doi:10.1038/s41928-022-00785-z

A reconfigurable integration technology based on stackable chips with embedded arrays of optoelectronic devices and memristive crossbars could be of use in edge intelligence applications.

Nature Communications, Published online: 17 June 2022; doi:10.1038/s41467-022-30909-0

Photonic topological insulators offer unconventional, yet still difficult, ways to control light flow. Here the authors demonstrate a 3D photonic topological insulator with surface states confined and guided on the surfaces without adding any cladding.

An ultralow power consumption force field-effect transistor with large modulation by the FE in 2D MoS₂ is demonstrated. A new principle for mechanical modulation can realize ultrahigh electromechanical resolution (nano-Newton) and sensitivity (GF >4801), and this process only consumes atto-Joule energy and the leakage power approaches zero, indicating the direction for the next generation of low-power electronics.

Abstract

In addition to electrical, optical, and magnetic fields, mechanical forces have demonstrated a strong ability to modulate semiconductor devices. With the rapid development of piezotronics and flexotronics, force regulation has been widely used in field-effect transistors (FETs), human–machine interfaces, light-emitting diodes (LEDs), solar cells, etc. Here, a large mechanical modulation of electronic properties by nano-Newton force in semiconductor materials with a large Young's modulus-based force FET is reported. More importantly, this FET has ultralow switching energy dissipation (7 aJ per decuple current gain) and nearly zero leakage power; these values are even better than those of electronic FETs. This finding paves the way for practical applications of nanoforce modulation devices at high power efficiency.

The synthesis of a Nb, Re dual-doped monolayer WSe₂ with the phase modulation is reported. The as-synthesized Nb, Re-WSe₂ demonstrates an ultrasensitive molecular sensing performance with a record low concentration of 5 × 10^–15 m, which is superior to that of most state-of-the-art non-noble metal substrates, and exhibits excellent environmental stability (≈6 months) and selective detection.

Abstract

Surface-enhanced Raman scattering (SERS) is a sensitive, fast, and nondestructive technology to detect trace amounts of molecules. The development of ultrasensitive and environmentally stable noble-metal-free SERS substrates is crucial for practical applications but still very challenging. In this contribution, an in situ substitutional doping strategy to synthesize Re-doped WSe₂ (Re-WSe₂) with different doping levels is reported. By increasing the Re content to ≈50 at%, the Re-WSe₂ alloy inherits the 1T″ phase of the ReSe₂ lattice. Furthermore, Nb atoms are doped into the 1T″ Re-WSe₂ alloy to further modulate its electronic structure. The as synthesized 1T″ Nb, Re-WSe₂ demonstrates a femtomolar-level molecular sensing capability with a detectable concentration of 5 × 10^–15 m and the corresponding enhancement factor is 2.0 × 10⁹, which is superior to that of most non-noble-metal SERS substrates and comparable or even superior to that of noble-metal substrates to the best of the authors’ knowledge. More importantly, the as-synthesized 1T″ Nb, Re-WSe₂ exhibits excellent air-stability over a long term (≈6 months) and selective detection capability in the mixed molecular solution, which are essential for their practical applications. The work provides a new strategy for the rational design of noble-metal-free SERS substrates to achieve ultrasensitive molecular sensing.

An approach to control a metal–insulator transition (MIT) behavior in a vanadium dioxide is demonstrated by employing the heteroepitaxial Mott transistor. Due to the defect-alleviated interfaces, the enhanced coupling between the correlated electrons and ferroelectricity is successfully proven by showing a nonvolatile MIT behavior through the reversible memory performance.

Abstract

Controlling phase transitions in correlated materials yields emergent functional properties, providing new aspects to future electronics and a fundamental understanding of condensed matter systems. With vanadium dioxide (VO₂), a representative correlated material, an approach to control a metal–insulator transition (MIT) behavior is developed by employing a heteroepitaxial structure with a ferroelectric BiFeO₃ (BFO) layer to modulate the interaction of correlated electrons. Owing to the defect-alleviated interfaces, the enhanced coupling between the correlated electrons and ferroelectric polarization is successfully demonstrated by showing a nonvolatile control of MIT of VO₂ at room temperature. The ferroelectrically-tunable MIT can be realized through the Mott transistor (VO₂/BFO/SrRuO₃) with a remanent polarization of 80 µC cm⁻², leading to a nonvolatile MIT behavior through the reversible electrical conductance with a large on/off ratio (≈10²), long retention time (≈10⁴ s), and high endurance (≈10³ cycles). Furthermore, the structural phase transition of VO₂ is corroborated by ferroelectric polarization through in situ Raman mapping analysis. This study provides novel design principles for heteroepitaxial correlated materials and innovative insight to modulate multifunctional properties.

Integrated photonic memory based on a novel phase-change material—namely, Sc_0.2Sb₂Te₃ (SST)—showing distinct optical contrast between two stable phases, amorphous and crystalline states is reported. Using an optical pulse as fast as 2 ns, information can be written and erased in the photonic memory. This ultrafast photonic memory has enormous application potential in photonic computing and neuromorphic computing applications.

Abstract

The search for ultrafast photonic memory devices is inspired by the ever-increasing number of cloud-computing, supercomputing, and artificial-intelligence applications, together with the unique advantages of signal processing in the optical domain such as high speed, large bandwidth, and low energy consumption. By embracing silicon photonics with chalcogenide phase-change materials (PCMs), non-volatile integrated photonic memory is developed with promising potential in photonic integrated circuits and nanophotonic applications. While conventional PCMs suffer from slow crystallization speed, scandium-doped antimony telluride (SST) has been recently developed for ultrafast phase-change random-access memory applications. An ultrafast non-volatile photonic memory based on an SST thin film with a 2 ns write/erase speed is demonstrated, which is the fastest write/erase speed ever reported in integrated phase-change photonic devices. SST-based photonic memories exhibit multilevel capabilities and good stability at room temperature. By mapping the memory level to the biological synapse weight, an artificial neural network based on photonic memory devices is successfully established for image classification. Additionally, a reflective nanodisplay application using SST with optoelectronic modulation capabilities is demonstrated. Both the optical and electrical changes in SST during the phase transition and the fast-switching speed demonstrate their potential for use in photonic computing, neuromorphic computing, nanophotonics, and optoelectronic applications.

Nature Materials, Published online: 16 June 2022; doi:10.1038/s41563-022-01285-3

Distinct electronic and optical properties emerge from quantum confinement in low-dimensional materials. Here, combining optical characterization and ab initio calculations, the authors report an unconventional excitonic state and bound phonon sideband in layered silicon diphosphide.

Nature Materials, Published online: 16 June 2022; doi:10.1038/s41563-022-01275-5

The authors show that an out-of-plane antidamping spin–orbit torque can produce a sizeable change in the switching dynamics of a magnetic layer with perpendicular anisotropy.

Nature Materials, Published online: 16 June 2022; doi:10.1038/s41563-022-01277-3

The authors use scanning tunnelling microscopy and spectroscopy to visualize the electronic structure of mirror twin boundaries, revealing a Tomonaga–Luttinger liquid.

A miniature amplifier with high power is realized with an ion-doped waveguide

An erbium-doped optical amplifier is fabricated on a silicon-nitride-based optical platform.

Nature, Published online: 16 June 2022; doi:10.1038/d41586-022-01653-8

A trap laid for indium atoms allows scientists to realize the first ultracold atoms of a ‘group 13’ element.

Recent advances and significant developments of chemical vapor deposition (CVD)-grown graphene toward flexible optoelectronics are comprehensively reviewed. The challenges of improvement of optoelectronic properties, work function tuning, as well as interfacial control of CVD-grown graphene for large-area optoelectronic devices are discussed. Various prototype devices are demonstrated, showing great potential for CVD-grown graphene in wearable optoelectronics.

Abstract

Graphene shows great potential for flexible optoelectronic devices owing to its unique 2D structure and excellent electronic, optical, and mechanical properties. Chemical vapor deposition (CVD) is the most promising method for fabricating large-area and high-quality graphene films at an acceptable cost; therefore enormous efforts have been attempted to investigate the flexible optoelectronic devices based on CVD-grown graphene. Here, recent advances and significant development of CVD-grown graphene towards flexible optoelectronics including photodetectors, organic solar cells, and light-emitting diodes are reviewed. Insight into the challenges of improvement of optoelectronic properties, work function tuning, as well as interfacial control of CVD-grown graphene for high-performance devices is provided. In particular, the availability to fabricate large-area devices on the flexible substrates is discussed, which is crucial to drive the practical use of CVD-grown graphene for future wearable optoelectronics.

A new platform of stacked polyethylene single crystal and monolayer MoSe₂ is created to accurately measure the mechanical properties of polymer single crystals where monolayer MoSe₂ provides strong mechanical support to enable a suspended stack over micro-holes. This structure also represents an ultimate polymer-ceramic crystalline laminate that may be modeled as a composite unit for complex composite design.

Abstract

Polymer single crystal (SC) is a key building block of semicrystalline polymers. However, direct experimental measurement of freestanding mono-lamella polymer SC has not been demonstrated. This is, in large part, due to the difficulties associated with manipulating freestanding individual mono-lamella SC because of its extremely low rigidity and low robustness. Here, we demonstrate a new strategy to successfully suspend and test a polymer SC by using a 2D material as backing. In particular, mono-lamella polyethylene (PE) SC is stacked on monolayer MoSe₂, and the hybrid stacks can be suspended over microholes. Nanoindentation is used to probe the suspended PE-SC/MoSe₂ stacks and MoSe₂ monolayers. The results suggest the first experimentally-measured in-plane moduli of PE-SC and 2D MoSe₂ as 32 ± 3 and 237 ± 15 GPa, respectively. Such a stacked unit represents an ultrathin structure of polymer-ceramic laminate and the idea can be applied to other laminated composite systems. Therefore, this research will pave the way to accurately measure the mechanical properties of polymer SCs and their composites, as well as provide a key insight on designing composite structures.

Ultrasensitive solar-blind ultraviolet photodetector based on FePSe₃/MoS₂ heterodiode is demonstrated. The exciting experimental results include a high R of 33 600 A W⁻¹, which is the highest performance compared with the state-of-the-art 2D material SBUV detectors, the noise equivalent power lower than 5.7 × 10^-16 W Hz^−1/2, high D* of 1.51 ×  10¹³ cm Hz^1/2 W⁻¹ in SBUV (230–280 nm) range. This finding promotes the development of SBUV photodetectors.

Abstract

Metal phosphorous tri-chalcogenides are a category of new ternary 2D layered materials with a wide range of tuneable bandgaps (1.2–3.5 eV). These wide-bandgap semiconductors exhibit great potential applications in solar-blind ultraviolet (SBUV) photodetection. However, these 2D solar-blind photodetectors suffer from low photoresponsivity, slow photoresponse speed, and narrow operation spectral region, thereby limiting their practical applications. Here, an ultra-broadband photodetection based on a FePSe₃/MoS₂ heterostructure with coverage ranging from solar-blind ultraviolet 265 nm to longwave infrared (LWIR) 10.6 µm is reported. Notably, the device exhibits excellent weak light detection capability. A high photoresponsivity of 33 600 A W⁻¹ and an external quantum efficiency of 1.57 × 10⁷% are demonstrated. A noise-equivalent power as low as 5.7 ×  10^–16 W Hz^−1/2 and a specific detectivity up to 1.51 × 10¹³ cm Hz^1/2 W⁻¹ are realized in the SBUV region. The room temperature LWIR photoresponsivity of 0.12 A W⁻¹ is realized. This work opens a route to design high-performance SBUV photodetectors and wide spectral photoresponse applications.