Jing Zhang

Nature, Published online: 09 November 2022; doi:10.1038/d41586-022-03337-9

Perovskites are promising candidates for use in next-generation light-emitting diode (LED) displays that are vivid and have high colour quality. LEDs made from particles with a perovskite nanocrystal core and an acidic shell are efficient and bright, and have a long operational half-life.

Pyridine-based Ir(III) complexes have been rationally designed to improve their emission brightness. The blue phosphorescent organic light-emitting diodes based on complex 3 dopant (functionalized with new −CF₃ ligand) exhibit excellent performance with a maximum external quantum efficiency of 22.0% and extremely low efficiency roll-off. Upon increasing the current density to 250 mA cm⁻², high brightness value of 53 400 cd m⁻² is achieved.

Abstract

Herein, a family of six [3+2+1] coordinated 2-(2′,4′-difluorophenyl) pyridine-based Iridium(III) complexes with intermolecular interactions have been designed to improve their emission properties. These molecular interactions have been regarded as an effective way to suppress non-radiative decay and enhance the photoluminescence quantum yield (PLQY) of the light-emitting materials. Specifically, complex 3 functionalized with new −CF₃ ligand exhibits PLQY of up to 100%, and the emission peak at ≈485 nm with short excited-state lifetime down to 1 µs. Therefore, the blue phosphorescent organic light-emitting diode (OLED) based on complex 3 dopant exhibits excellent performance with a maximum external quantum efficiency of 22.0% and low efficiency roll-off. Upon increasing the current density to 250 mA cm⁻², high brightness value of 53 400 cd m⁻² is achieved, which is not attainable with the similar molecular structure that we have reported recently, indicating the importance of the presence of the (CF···H/CN···H) interactions. Given the well-overlapping of the emission spectra of these Iridium(III) complexes and absorption spectrum of v-DABNA emitter, complex 3 has been successfully applied as a sensitizer for v-DABNA-based OLED, and a maximum current efficiency of 27.13 cd A⁻¹ with high brightness level of up to 10 000 cd m⁻² have been achieved.

Graphene is a promising candidate for application in spintronic devices and quantum computation. Herein, it is demonstrated that Co grafted graphene shows robust room temperature ferromagnetism via Co d _xz and graphene p _z orbital hybridization. It is also identified that the origin behind the magnetic interaction of Co-C ions is mediated by spin polarized graphene p _z orbitals, and the room temperature ferromagnetism can be stabilized by electron doping.

Abstract

Graphene-based magnetic materials exhibit novel properties and promising applications in the development of next-generation spintronic devices. Modern synthesis techniques have paved the way to design precisely the local environments of metal atoms anchored onto a nitrogen-doped graphene matrix. Herein, it is demonstrated that grafting cobalt (Co) into the graphene lattice induces robust and stable room-temperature ferromagnetism. These comprehensive experiments and first-principles calculations unambiguously identify that the mechanism for this unusual ferromagnetism is π-d orbital hybridization between Co d_xz and graphene p_z orbitals. Here, it is found that the magnetic interactions of Co–carbon ions are mediated by the spin-polarized graphene p_z orbitals, and room temperature ferromagnetism can be stabilized by electron doping. It is also found that the electronic structure near the Fermi level, which sets the nature of spin polarization of graphene p_z bands, strongly depends on the local environment of the Co moiety. This is the crucial, previously missing, ingredient that enables control of the magnetism. Overall, these observations unambiguously reveal that engineering the atomic structure of metal-embedded graphene lattices through careful d to p orbital interactions opens a new window of opportunities for developing graphene-based spintronics devices.

How to effectively extract the energetic electrons from plasmonic metal and prolong their lifetimes is a daunting challenge for plasmon-assisted chemistry. Here, it is demonstrated that in contrast to Au/CsPbBr₃ directly connected system showing severe plasmon-exciton suppression, Au@CdS/CsPbBr₃ ternary heteronanocrystals with judiciously engineered interfaces enable to leverage the exceptional hot carrier dynamics of halide perovskite and acquire ultralong-lived plasmon-excited electrons.

Abstract

Combination of the strong light-absorbing power of plasmonic metals with the superior charge carrier dynamics of halide perovskites is appealing for bio-inspired solar-energy conversion due to the potential to acquire long-lived plasmon-induced hot electrons. However, the direct coupling of these two materials, with Au/CsPbBr₃ heteronanocrystals (HNCs) as a prototype, results in severe suppression of plasmon resonances. The present work shows that interfacial engineering is a key knob for overcoming this impediment, based on the creation of a CdS mediate layer between Au and CsPbBr₃ forming atomically organized Au-CdS and CdS-CsPbBr₃ interfaces by nonepitaxial/epitaxial combined strategy. Transient spectroscopy studies demonstrate that the resulting Au@CdS/CsPbBr₃ HNCs generate remarkably long-lived plasmon-induced charge carriers with lifetime up to nanosecond timescale, which is several orders of magnitude longer than those reported for colloidal plasmonic metal-semiconductor systems. Such long-lived carriers extracted from plasmonic antennas enable to drive CO₂ photoreduction with efficiency outperforming previously reported CsPbBr₃-based photocatalysts. The findings disclose a new paradigm for achieving much elongated time windows to harness the substantial energy of transient plasmons through realization of synergistic coupling of plasmonic metals and halide perovskites.

Compared with traditional silicon-based devices, the unique features of all-2D electronics are atomic flatness and dangling-bond van der Waals interfaces, including all-2D metal/semiconductor, all-2D semiconductor/semiconductor, and all-2D dielectric/semiconductor interfaces. These interfaces provide an excellent device platform for removing lattice matching constraints, suppressing carrier scattering, and exploiting new physical effects.

Abstract

The interface is the device. As the feature size rapidly shrinks, silicon-based electronic devices are facing multiple challenges of material performance decrease and interface quality degradation. Ultrathin 2D materials are considered as potential candidates in future electronics by their atomically flat surfaces and excellent immunity to short-channel effects. Moreover, due to naturally terminated surfaces and weak van der Waals (vdW) interactions between layers, 2D materials can be freely stacked without the lattice matching limit to form high-quality heterostructure interfaces with arbitrary components and twist angles. Controlled interlayer band alignment and optimized interfacial carrier behavior allow all-2D electronics based on 2D vdW interfaces to exhibit more comprehensive functionality and better performance. Especially, achieving the same computing capacity of multiple conventional devices with small footprint all-2D devices is considered to be the key development direction of future electronics. Herein, the unique properties of all-2D vdW interfaces and their construction methods are systematically reviewed and the main performance contributions of different vdW interfaces in 2D electronics are summarized, respectively. Finally, the recent progress and challenges for all-2D vdW electronics are discussed, and how to improve the compatibility of 2D material devices with silicon-based industrial technology is pointed out as a critical challenge.

Nature Nanotechnology, Published online: 09 November 2022; doi:10.1038/s41565-022-01275-1

Self-assembled monolayers nicely link the history and the future of nanoscience and nanotechnology.

The phase transition, multiple valence bands, and resonant bonding endow GeTe with promising thermoelectric performance. Significant breakthroughs are achieved in GeTe-based materials. This review summarizes the recent progress in developing high-performance GeTe-based materials and devices, including the underlying fundamentals, large-scale production, novel strategies for boosting performance, and techniques of device assembly.

Abstract

Driven by the intensive efforts in the development of high-performance GeTe thermoelectrics for mass-market application in power generation and refrigeration, GeTe-based materials display a high figure of merit of >2.0 and an energy conversion efficiency beyond 10%. However, a comprehensive review on GeTe, from fundamentals to devices, is still needed. In this regard, the latest progress on the state-of-the-art GeTe is timely reviewed. The phase transition, intrinsic high carrier concentration, and multiple band edges of GeTe are fundamentally analyzed from the perspectives of the native atomic orbital, chemical bonding, and lattice defects. Then, the fabrication methods are summarized with a focus on large-scale production. Afterward, the strategies for enhancing electronic transports of GeTe by energy filtering effect, resonance doping, band convergence, and Rashba band splitting, and the methods for strengthening phonon scatterings via nanoprecipitates, planar vacancies, and superlattices, are comprehensively reviewed. Besides, the device assembly and performance are highlighted. In the end, future research directions are concluded and proposed, which enlighten the development of broader thermoelectric materials.

Nature Communications, Published online: 07 November 2022; doi:10.1038/s41467-022-34453-9

Perovskite nanomaterials may suffer degradation during conventional photolithography. Here, the authors report a non-destructive method for patterning perovskite quantum dots based on direct photopolymerization catalyzed by lead bromide complexes.

Nature Electronics, Published online: 07 November 2022; doi:10.1038/s41928-022-00872-1

Artificial synapses made of indium selenide can exhibit tunable temporal dynamics, which can be used to achieve multisensory fusion and multiple-timescale feature extraction in reservoir computing.

A passive mode-locked Er-doped fiber laser based on the Bi₂O₂Te saturable absorber is proposed. Various switchable and stable mode-locking states including conventional soliton, soliton molecules, and harmonic mode-locking states can be realized in the same cavity. The results reveal that Bi₂O₂Te nanosheets have excellent nonlinear optical modulation properties.

Abstract

As a recent addition to the emerging 2D bismuth oxychalcogenides (Bi₂O₂ X, where X = S, Se, and Te), atomically-thin bismuth oxytellurium (Bi₂O₂Te) exhibits unique thermoelectric and photoelectric properties. In this study, high-quality Bi₂O₂Te nanosheets (NSs)-based saturable absorber (SA) with a modulation depth of 8.2% is developed using the liquid phase exfoliation (LPE) method and is successfully applied to a passively mode-locked Er-doped fiber laser (EDFL) for the first time (with reference to the available literature). Due to the excellent nonlinear saturable absorption property of Bi₂O₂Te NSs, various switchable and stable mode-locking states can be realized in the same EDFL, including fundamental frequency conventional soliton (CS), soliton molecules, and harmonic mode-locking (HML) states. Among them, the CS pulse at 7.48 MHz (fundamental frequency) with a high signal-to-noise ratio (SNR) of 67.25 dB is obtained. The 2nd, 3rd, and 4th-order soliton molecules are observed with a soliton pulse separation of ≈6.2 ps. Moreover, for HML, a maximum repetition rate of 1.78 GHz (i.e., corresponding to the 238th-order harmonic) is obtained. The results reveal that Bi₂O₂Te NSs demonstrate excellent nonlinear optical modulation properties and can serve as a fundamental basis for promotion of academic research and innovation of engineering applications involving ultrafast photonics.

Transition-metal carbides/nitrides (MXene)-organic single crystal vertical transistor exhibits a fast switching characteristic under an ultralow operating voltage of −1 mV, meanwhile consumes only 8.7 aJ per spike when working as an electrical synaptic transistor.

Abstract

Organic field-effect transistors with parallel transmission and learning functions are of interest in the development of brain-inspired neuromorphic computing. However, the poor performance and high power consumption are the two main issues limiting their practical applications. Herein, an ultralow-power vertical transistor is demonstrated based on transition-metal carbides/nitrides (MXene) and organic single crystal. The transistor exhibits a high J _ON of 16.6 mA cm⁻² and a high J _ON/J _OFF ratio of 9.12 × 10⁵ under an ultralow working voltage of −1 mV. Furthermore, it can successfully simulate the functions of biological synapse under electrical modulation along with consuming only 8.7 aJ of power per spike. It also permits multilevel information decoding modes with a significant gap between the readable time of professionals and nonprofessionals, producing a high signal-to-noise ratio up to 114.15 dB. This work encourages the use of vertical transistors and organic single crystal in decoding information and advances the development of low-power neuromorphic systems.

Nature Materials, Published online: 04 November 2022; doi:10.1038/s41563-022-01408-w

Scientists have designed a foldable, mechanical analogue of integrated circuits that could be used as a platform to fabricate intelligent metamaterials.

We report on observation of the infrared photoresistance of twisted bilayer graphene (tBLG) under continuous quantum cascade laser illumination at a frequency of 57.1 THz. The photoresistance shows an intricate sign-alternating behavior under variations of temperature and back gate voltage, and exhibits giant resonance-like enhancements at certain gate voltages. The structure of the photoresponse correlates with weaker features in the dark dc resistance reflecting the complex band structure of tBLG. It is shown that the observed photoresistance is well captured by a bolometric model describing the electron and hole gas heating, which implies an ultrafast thermalization of the photoexcited electron–hole pairs in the whole range of studied temperatures and back gate voltages. We establish that photoresistance can serve a highly sensitive probe of the temperature variations of electronic transport in tBLG.

Morphological Information Encryption

In article number 2206912, Wu, Zhang, Chen, and co-workers apply short alkyl chains modified polyvinyl alcohol as a molecular switch to control the static deformation of shape memory hydrogel. Thus, the hydrogel morphologies can be encoded with encrypted morphological information, furtherly delivering hierarchical and continuous morphological information with the assistance of programmed near-infrared light.

The short alkyl chains modified polyvinyl alcohol (PVA-C6) is utilized as a molecular switch to control the static deformation of shape memory hydrogel via thermo-responsive hydrophobic clusters. Thus, the hydrogel morphologies can be encoded into encrypted morphological information, furtherly delivering hierarchical and continuous morphological information with the assistance of programmed near-infrared light.

Abstract

Morphological information encryption such as gesture and sign language is a traditional but efficient way of information storage and communication. However, due to the limited deformability, almost all of the existing information encryption materials store and deliver information via the pattern or color changes on the 2D plane. Herein, a thermo and ion dual-responsive shape memory hydrogel containing short alkyl chains modified polyvinyl alcohol (PVA-C6) and polyacrylamide-co-polyacrylic acid [P(AAm-co-AAc)], is prepared. In this system, the ion-responsive shape memory process of P(AAm-co-AAc) provides the preprogrammed morphological information and actuating force while the thermo-responsive hydrophobic clusters of PVA-C6 are utilized as a molecular switch to control the deformed posture within the deformation process. Incorporated with a photothermal particle, Fe₃O₄, the photothermal PVA-C6 hydrogel is capable of generating diverse configurations that can be encoded as the corresponding information. With the assistance of the programmable NIR, the hydrogel can transfer to the encoded configuration and decrypt the information. Besides, the obtained morphological information can also be erased by immersing the hydrogel in hot water, in order to avoid the leakage of information. This study motivates the design and fabrication of deformable materials and provides a new insight into the information encrypt materials.

Light-Emitting Devices

A color-tunable light-emitting diode is realized by Jiang Pu, Yasumitsu Miyata, Taishi Takenobu, and co-workers in article number 2203250 using compositionally graded monolayer transition metal dichalcogenide alloys. By controlling the light-emitting positions in the alloys, the composition gradient of the bandgap enables continuous and reversible light emission with energies ranging from 2.1 to 1.7 eV. The results provide a new approach for exploring monolayer semiconductor alloy based broadband optoelectronic device applications.

Robotic Skin

In article number 2204805, Jae-Woong Jeong and co-workers report an adaptive robotic skin with an augmented pressure-sensing capability beyond that of human skin. The robotic skin is composed of gallium microgranules fabricated uniformly using a T-junction microfluidic system. Through the phase transition of gallium microgranules, it achieves a higher sensitivity in the soft mode and a broader dynamic range in the rigid mode compared to human skin.

Scalable approaches of high-quality mono/multilayer hexagonal boron nitride (h-BN) synthesis are reviewed, the challenges and opportunities for each method are discussed, and their relevance to emerging applications is contextualized. Maintaining stoichiometric balance B:N = 1 in the growing crystal and enabling stacking order between layers emerge as the main challenges. Advances in these aspects will inform/guide the synthesis of other 2D materials with >1 constituent element.

Abstract

Hexagonal boron nitride (h-BN) is a layered inorganic synthetic crystal exhibiting high temperature stability and high thermal conductivity. As a ceramic material it has been widely used for thermal management, heat shielding, lubrication, and as a filler material for structural composites. Recent scientific advances in isolating atomically thin monolayers from layered van der Waals crystals to study their unique properties has propelled research interest in mono/few layered h-BN as a wide bandgap insulating support for nanoscale electronics, tunnel barriers, communications, neutron detectors, optics, sensing, novel separations, quantum emission from defects, among others. Realizing these futuristic applications hinges on scalable cost-effective high-quality h-BN synthesis. Here, the authors review scalable approaches of high-quality mono/multilayer h-BN synthesis, discuss the challenges and opportunities for each method, and contextualize their relevance to emerging applications. Maintaining a stoichiometric balance B:N = 1 as the atoms incorporate into the growing layered crystal and maintaining stacking order between layers during multi-layer synthesis emerge as some of the main challenges for h-BN synthesis and the development of processes to address these aspects can inform and guide the synthesis of other layered materials with more than one constituent element. Finally, the authors contextualize h-BN synthesis efforts along with quality requirements for emerging applications via a technological roadmap.

Emerging 2D metal oxides exhibit intriguing electronic and optical properties, which have great potential in emerging functional devices. Diverse structures and various synthesis methods open a new field of vision for device-fabrication-based 2D metal oxides. Their unique properties can bring new vigor and vitality into 2D material family.

Abstract

2D metal oxides have aroused increasing attention in the field of electronics and optoelectronics due to their intriguing physical properties. In this review, an overview of recent advances on synthesis of 2D metal oxides and their electronic applications is presented. First, the tunable physical properties of 2D metal oxides that relate to the structure (various oxidation-state forms, polymorphism, etc.), crystallinity and defects (anisotropy, point defects, and grain boundary), and thickness (quantum confinement effect, interfacial effect, etc.) are discussed. Then, advanced synthesis methods for 2D metal oxides besides mechanical exfoliation are introduced and classified into solution process, vapor-phase deposition, and native oxidation on a metal source. Later, the various roles of 2D metal oxides in widespread applications, i.e., transistors, inverters, photodetectors, piezotronics, memristors, and potential applications (solar cell, spintronics, and superconducting devices) are discussed. Finally, an outlook of existing challenges and future opportunities in 2D metal oxides is proposed.

The formation of ultrathin nanowires has thermodynamic advantages at low temperature. However, at low temperatures the monomers for nanocrystal growth are difficult to generate through precursor decomposition. In their Research Article (e202212251), Di Qiu, Yaping Du, and co-workers report an efficient growth process based on adding polyoxometalate clusters to the monomers. Fifteen types of rare earth oxide ultrathin nanowires were synthesized, all exhibiting polymer-like behavior due to the extremely high aspect ratio.

This review focuses on FET-based tactile pressure sensors. The working principles of this kind of tactile sensors are discussed in detail, the state-of-the-art protocols for high-performance tactile sensing are highlighted, and the major advances in large-scale tactile sensor arrays and their applications in robotics, health care, and smart manufacturing in terms of transistor matrix are also introduced.

Abstract

The past several decades have witnessed great progress in high-performance field effect transistors (FET) as one of the most important electronic components. At the same time, due to their intrinsic advantages, such as multiparameter accessibility, excellent electric signal amplification function, and ease of large-scale manufacturing, FET as tactile sensors for flexible wearable devices, artificial intelligence, Internet of Things, and other fields to perceive external stimuli has also attracted great attention and become a significant field of general concern. More importantly, FET has a unique three-terminal structure, which enables its different components to detect external mechanics through different sensing mechanisms. On one hand, it provides an important platform to shed deep insights into the underlying mechanisms of the tactile sensors. On the other hand, these properties could in turn endow excellent components for the construction of tactile matrix sensor arrays with high quality. With special emphasis on the configuration of FETs, this review classified and summarized structure-optimized FET tactile sensors with gate, dielectric layer, semiconductor layer, and source/drain electrodes as sensing active components, respectively. The working principles and the state-of-the-art protocols in terms of high-performance tactile sensors are detail discussed and highlighted, the innovative pixel distribution and integration analysis of the transistor sensor matrix array concerning flexible electronics are also introduced. We hope that the introduction of this review can provide some inspiration for future researchers to design and fabricate high-performance FET-based tactile sensor chips for flexible electronics and other fields.