Jiuxiang Dai

This review summarizes the structural modification strategies of organic small-molecule semiconductors with high electron mobilities, a promising candidate for the construction of next-generation complementary organic logic-digital circuits, to achieve chemical stability and high electron transport properties. In addition, the applications of n-type small-molecule semiconductor materials based on high mobility in organic electronic devices, such as organic field-effect transistors, organic light-emitting transistors, organic photodetectors, and gas sensors, are introduced.

Abstract

Organic electronics has made great progress in the past decades, which is inseparable from the innovative development of organic electronic devices and the diversity of organic semiconductor materials. It is worth mentioning that both of these great advances are inextricably linked to the development of organic high-performance semiconductor materials, especially the representative n-type organic small-molecule semiconductor materials with high electron mobilities. The n-type organic small molecules have the advantages of simple synthesis process, strong intermolecular stacking, tunable molecular structure, and easy to functionalize structures. Furthermore, the n-type semiconductor is a remarkable and important component for constructing complementary logic circuits and p-n heterojunction structures. Therefore, n-type organic semiconductors play an extremely important role in the field of organic electronic materials and are the basis for the industrialization of organic electronic functional devices. This review focuses on the modification strategies of organic small molecules with high electron mobility at molecular level, and discusses in detail the applications of n-type small-molecule semiconductor materials with high mobility in organic field-effect transistors, organic light-emitting transistors, organic photodetectors, and gas sensors.

Nature Materials, Published online: 15 December 2022; doi:10.1038/s41563-022-01444-6

Thermal Hall conductivity originating from topological magnons is observed in the Kitaev candidate α-RuCl3 in broad intervals of temperature and in-plane magnetic field, raising questions on the role of the Majorana mode in heat conduction.

Nature Communications, Published online: 15 December 2022; doi:10.1038/s41467-022-34812-6

One particularly useful feature of van der Waals materials is the ability to combine layers of different materials into a single heterostructure, which can have superior properties than any of the constituent materials alone. Here, Cheng et al. combine two interlayer-antiferromagnetic chromium trihalides, CrI3 and CrCl3 in close proximity, and demonstrate ferromagnetic coupling between them.

Nature Materials, Published online: 14 December 2022; doi:10.1038/s41563-022-01445-5

A combination of tunnelling spectroscopy, magnetotransport, electron diffraction and ab initio calculations have revealed that picometre-scale lattice distortions reverse magnetic anisotropy and enhance magnetic frustration in atomically thin ruthenium trichloride — a key step towards realizing a quantum spin liquid in the two-dimensional limit.

Nature Communications, Published online: 14 December 2022; doi:10.1038/s41467-022-35290-6

Unsatisfied electrode bonding in half-Heusler devices limits their practical service at high temperatures. Here, the authors develop a direct bonding interface to ideal ohmic contact and thermally inert and ohmic contact, leading to high deficiency.

Nature Materials, Published online: 13 December 2022; doi:10.1038/s41563-022-01423-x

Zhu-Jun Wang and Zhi Liu discuss how advanced characterization technologies have helped to understand ancient man-made materials and human history.

A self-powered flexible optical writing device based on the two-dimensional position-sensitive photothermoelectric effect of SnSe thin film is demonstrated. Laser positioning, tracking, and recognition of characters optically written are realized by measuring the bi-directional output voltages assisted with deep learning.

Abstract

The photothermoelectric (PTE) effect enables a simple structure to construct a noncontact and self-powered writing device. PTE detectors based on active materials and one-dimensional (1D) position-sensitive PTE effect have attracted considerable attentions. However, there is no research on applying the 1D position-sensitive PTE effect to a two-dimensional (2D) surface. Besides, flexible writing devices based on the PTE effect have not been reported. Here, we demonstrate a self-powered flexible optical writing device based on the 2D position-sensitive PTE effect of SnSe thin film. Laser positioning, tracking, and distinguishing of optically written characters have been realized by only measuring the bi-directional output voltages during the writing process. A deep convolutional neural network has been introduced to recognize optically written numbers and characters with high recognition accuracy (92%) and fast processing speed (8.6 ms). The flexible optical-writing device with a simple structure could rapidly and accurately recognize characters in a noncontact fashion using a small amount of training data.

By introducing a cryogenic environment to suppress the harmful cross relaxation, the upconversion intensity of Er³⁺-rich core–shell structures can be significantly improved over 100-fold, together with an over 50-fold modulation on the red-to-green emission ratio.

Abstract

Relatively low efficiency is the bottleneck for the application of lanthanide-doped upconversion nanoparticles (UCNPs). The high-level doping strategy realized in recent years has not improved the efficiency as much as expected. It is argued that cross relaxation (CR) is not detrimental to upconversion. Here we combine theoretical simulation and spectroscopy to elucidate the role of CR in upconversion process of Er³⁺ highly doped (HD) UCNPs. It is found that if CR is purposively suppressed, upconversion efficiency can be significantly improved. Specifically, we demonstrate experimentally that inhibition of CR by introducing cryogenic environment (40 K) enhances upconversion emission by more than two orders of magnitude. This work not only elucidates the nature of CR and its non-negligible adverse effects, but also provides a new perspective for improving upconversion efficiency. The result can be directly applied to cryogenic imaging and wide range temperature sensing.

Nature Communications, Published online: 13 December 2022; doi:10.1038/s41467-022-35339-6

Layer dependence is an important aspect to properties of van der Waals materials. Here, the authors obtain layer dependent multiple polarization states in 3 R MoS2 and propose a generalized model to describe their ferroelectric switching processes.

Nature Electronics, Published online: 12 December 2022; doi:10.1038/s41928-022-00880-1

The magnetic exchange interaction of MnBi2Te4—an intrinsic magnetic topological insulator—can be tuned by intercalating ferromagnetic layers of MnTe.

Nature Electronics, Published online: 12 December 2022; doi:10.1038/s41928-022-00882-z

The magnetic anisotropy of the van der Waals ferromagnet Fe5GeTe2 can be continuously tuned—from an initial out-of-plane orientation to a canted orientation and then finally to an in-plane orientation—using electrical gating.

Nature Electronics, Published online: 12 December 2022; doi:10.1038/s41928-022-00899-4

Two-dimensional semiconductors can be used as a channel material in gate-all-around nanosheet field-effect transistors.

Nature Nanotechnology, Published online: 12 December 2022; doi:10.1038/s41565-022-01257-3

A chemical-vapour-deposition-based approach enables the phase-controllable synthesis of large-scale two-dimensional β-, β′- and α-In2Se3 films.

Nature Nanotechnology, Published online: 12 December 2022; doi:10.1038/s41565-022-01263-5

Manipulation of vacancy and strain enables fabrication of large area, phase-controllable 2D ferroelectric materials and their hetero-phase junction.

A method to continuously supply carbon from one side of Cu substrate while maintaining a sustained growth of multilayer graphene on the other side by separately controlling the atmosphere on the two sides is provided. The study contributes to the controllable growth of graphene films in terms of layer numbers.

Because of the very low C solubility, Cu substrates possess a great advantage in growing the graphene film of monolayer or few layers with well-developed uniformity. The self-limited growth manner ensures the growth of nearly pure monolayer graphene, but it prevents the supply of C for the growth of adlayers after the complete growth of the top layer. Herein, a method to continuously supply C from one side of Cu substrate while maintaining sustained growth of multilayer graphene on the other side by separately controlling the atmosphere on two sides is studied. The growth rate and thickness of graphene can be controlled by tuning the oxygen flow and postgrowth time. Multilayer graphene with thickness (t) up to 100 nm is achieved. It demonstrates a potential application in terahertz shielding with a high shielding effectiveness (SE) of 25 dB and accordingly a high SE/t of 2.5 × 10⁵ dB/mm. The study contributes to the controllable growth of graphene films in terms of layer numbers and can be scaled up to large-area growth through the appropriate design of equipment.

With the development of science and technology, the application scenarios of flexible electronic devices are more diversified. However, the performance of traditional substrates can no longer meet the current requirements. Herein, to provide a new idea for the development of flexible high-efficiency electromagnetic devices, the characteristics, applications, and prospects of F-mica which has excellent performance are summarized.

Flexible electromagnetic devices are an important area of research in the twenty-first century. Although polymer substrates are the most commonly used transparent flexible substrates, they have certain disadvantages like low-temperature resistance and a high thermal expansion coefficient, limiting the preparation conditions of flexible devices and diminishing their performance. Herein, the characteristics and research status of inorganic flexible transparent fluorphlogopite are summarized. Herein, the structure, properties, and applications of fluorphlogopite are primarily discussed. Finally, the application of fluorphlogopite in flexible electromagnetic devices is envisioned so as to provide a novel idea for the development of high-performance flexible electromagnetic devices.

Recent developments in hafnia-based ferroelectric materials and their applications are comprehensively reviewed, with an in-depth analysis of ferroelectric transistors and their array structures. The relevant technological issues and their solutions are also discussed. This review provides a roadmap for the development of high-performance ferroelectric memory and neuromorphic devices based on ferroelectric transistors.

Abstract

Ferroelectric materials have been intensively investigated for high-performance nonvolatile memory devices in the past decades, owing to their nonvolatile polarization characteristics. Ferroelectric memory devices are expected to exhibit lower power consumption and higher speed than conventional memory devices. However, non-complementary metal–oxide–semiconductor (CMOS) compatibility and degradation due to fatigue of traditional perovskite-based ferroelectric materials have hindered the development of high-density and high-performance ferroelectric memories in the past. The recently developed hafnia-based ferroelectric materials have attracted immense attention in the development of advanced semiconductor devices. Because hafnia is typically used in CMOS processes, it can be directly incorporated into current semiconductor technologies. Additionally, hafnia-based ferroelectrics show high scalability and large coercive fields that are advantageous for high-density memory devices. This review summarizes the recent developments in ferroelectric devices, especially ferroelectric transistors, for next-generation memory and neuromorphic applications. First, the types of ferroelectric memories and their operation mechanisms are reviewed. Then, issues limiting the realization of high-performance ferroelectric transistors and possible solutions are discussed. The experimental demonstration of ferroelectric transistor arrays, including 3D ferroelectric NAND and its operation characteristics, are also reviewed. Finally, challenges and strategies toward the development of next-generation memory and neuromorphic applications based on ferroelectric transistors are outlined.

Abstract

Two-dimensional (2D) ferroelectric (FE) materials with relatively low switching barrier and large polarization are promising candidates for next-generation miniaturized nonvolatile memory devices. Herein, we screen out 39 new 2D ferroelectric materials, MX (M: Group III-V elements; X: Group V-VII elements), in three phosphorus-analogue phases including black phosphorene-like α-phase, blue phosphorus-like β-phase, and GeSe-like γ-phase using high-throughput calculations. Seven materials (α-SbP, γ-AsP, etc.) exhibit FE switching barriers lower than 0.3 eV/f.u., ferroelectric polarization larger than 2 × 10⁻¹⁰ C/m, and high thermodynamic stability with energy above hull smaller than 0.2 eV/atom. We find that the larger the electronegativity difference between M and X, the larger the ferroelectric polarization. Moreover, larger electronegativity differences result in lower in-plane piezoelectric stress tensor (e₁₁) for MX consisting of Group IV and VI elements and larger e₁₁ for those consisting of Group V elements. Further calculations predict a giant tunneling electroresistance in ferroelectric tunnel junction α-Sb(Sn)P/α-SbP/α-Sb(Te)P (1.26 × 10⁴%) and large piezoelectric strain coefficient in α-SnTe (396 pm/V), providing great opportunities to the design of non-volatile resistive memories, and high-performance piezoelectric devices.

npj 2D Materials and Applications, Published online: 09 December 2022; doi:10.1038/s41699-022-00361-1

High-performance junction-free field-effect transistor based on blue phosphorene

Batch synthesis of 12-inch transfer-free graphene with the aid of the hydroxyl groups released in situ from the substrates under a free molecular flow is realized, readily boosting oriented applications such as transparent heaters for 3D printing.

Abstract

Direct synthesis of large-area graphene on functional substrates via chemical vapor deposition has become a frontier research stream targeting practical applications. However, the batch production of transfer-free graphene film with favorable quality and homogeneity remains a grand challenge. Herein, the direct growth of 12-inch-sized graphene is demonstrated over fused quartz in a batch manner. The key design of the synthetic route is the construction of a nano-scale compartment to allow the formation of free molecular flow during growth, as well as to trap the hydroxyl species in situ released from the quartz substrates. Density functional theory calculations reveal that the hydroxyl species help decrease the energy barrier for feedstock decomposition and facilitate the carbon attachment to boost graphene growth. Thus-prepared graphene possesses excellent optical transmittance (96% ± 1%) and electrical properties (1.22 ± 0.08 kΩ sq^‒1). These findings unlock new opportunities for achieving batch production of graphene-skinned functional materials with practical scalability and quality toward emerging uses.

Nature Electronics, Published online: 08 December 2022; doi:10.1038/s41928-022-00881-0

By combining p-type transistors made with silicon-on-insulator technology and n-type transistors made with two-dimensional molybdenum disulfide, heterogeneous complementary field-effect transistors can be fabricated on the wafer scale.

Nature Nanotechnology, Published online: 08 December 2022; doi:10.1038/s41565-022-01299-7

2D materials for fast flash memory devices