Jiuxiang Dai

Fluorite-structured ferroelectrics are breakthrough materials for the development of ferroelectric memories for nanoscale electronic devices owing to their scalability and complementary metal–oxide–semiconductor (CMOS) compatibility as well as the availability of established deposition techniques. This review covers the history of ferroelectric memory based on conventional ferroelectric to recent research on fluorite-structured ferroelectrics and remaining issues to achieve large-scale integration for practical industrial applications.

Abstract

Over the last few decades, the research on ferroelectric memories has been limited due to their dimensional scalability and incompatibility with complementary metal-oxide-semiconductor (CMOS) technology. The discovery of ferroelectricity in fluorite-structured oxides revived interest in the research on ferroelectric memories, by inducing nanoscale nonvolatility in state-of-the-art gate insulators by minute doping and thermal treatment. The potential of this approach has been demonstrated by the fabrication of sub-30 nm electronic devices. Nonetheless, to realize practical applications, various technical limitations, such as insufficient reliability including endurance, retention, and imprint, as well as large device-to-device-variation, require urgent solutions. Furthermore, such limitations should be considered based on targeting devices as well as applications. Various types of ferroelectric memories including ferroelectric random-access-memory, ferroelectric field-effect-transistor, and ferroelectric tunnel junction should be considered for classical nonvolatile memories as well as emerging neuromorphic computing and processing-in-memory. Therefore, from the viewpoint of materials science, this review covers the recent research focusing on ferroelectric memories from the history of conventional approaches to future prospects.

Using an organic-inorganic hybrid double-layer dielectric, ideal, and environmentally stable charge transport is demonstrated in n-type polymer field-effect transistors. The fabricated polymer transistors exhibit high electron mobility of 1.49 ± 0.46 cm² V⁻¹ s⁻¹ with ideal reliability factors of 102 ± 7%. Moreover, the transistors show robust performance to organic solvent and high mobility above 1 cm² V⁻¹ s⁻¹ after storage in air for more than 300 days.

Abstract

Realizing ideal charge transport in field-effect transistors (FETs) of conjugated polymers is crucial for evaluating device performance, such as carrier mobility and practical applications of conjugated polymers. However, the current FETs using conjugated polymers as the active layers generally show certain non-ideal transport characteristics and poor stability. Here, ideal charge transport of n-type polymer FETs is achieved on flexible polyimide substrates by using an organic-inorganic hybrid double-layer dielectric. Deposited conjugated polymer films show highly ordered structures and low disorder, which are supported by grazing-incidence wide-angle X-ray scattering, near-edge X-ray absorption fine structure, and molecular dynamics simulations. Furthermore, the organic-inorganic hybrid double-layer dielectric provides low interfacial defects, leading to excellent charge transport in FETs with high electron mobility (1.49 ± 0.46 cm² V⁻¹ s⁻¹) and ideal reliability factors (102 ± 7%). Fabricated polymer FETs show a self-encapsulation effect, resulting in high stability of the FET charge transport. The polymer FETs still work with high mobility above 1 cm² V⁻¹ s⁻¹ after storage in air for more than 300 days. Compared with state-of-the-art conjugated polymer FETs, this work simultaneously achieves ideal charge transport and environmental stability in n-type polymer FETs, facilitating rapid device optimization of high-performance polymer electronics.

A breakthrough in room-temperature phosphorescence (RTP) emission performance was realized in a poly(vinylidene fluoride) (PVDF) matrix with a low glass transition temperature. Polymorph-dependent RTP emission in the PVDF matrix endows a 2.45 GHz microwave stimulus responsiveness to the material.

Abstract

The development of flexible, room-temperature phosphorescence (RTP) materials remains challenging owing to the quenching of their unstable triplet excitons via molecular motion. Therefore, a polymer matrix with T _g higher than room temperature is required to prevent polymer segment movement. In this study, a RTP material was developed by incorporating a 4-biphenylboronic acid (BPBA) phosphor into a poly(vinylidene fluoride) (PVDF) matrix (T _g=−27.1 °C), which exhibits a remarkable UV-light-dependent oxygen consumption phosphorescence with a lifetime of 1275.7 ms. The adjustable RTP performance is influenced by the crystallinity and polymorph (α, β, and γ phases) fraction of PVDF, therefore, the low T _g of the PVDF matrix enables the polymeric segmental motion upon microwave irradiation. Consequently, a reduction in the crystallinity and an increase in the α phase fraction in PVDF film induces RTP after 2.45 GHz microwave irradiation. These findings open up new avenues for constructing crystalline and phase-dependent RTP materials while demonstrating a promising approach toward microwave detection.

Single-domain β-Ga₂O₃ epitaxial films on sapphire substrates suppress boundary-induced recombination while having a low concentration of point defects and show efficient photogenerated charge separation. Tailored anti-reflection coating (ARC) with a forming gradient refractive index (n) not only substantially improves charge generation, but also suppresses dark current (I_dark) as passivation layers exhibiting a high-performance ultraviolet C photodetector.

Abstract

Implementing high-performance ultraviolet C photodetectors (UVC PDs) based on β-Ga₂O₃ films is challenging owing to the anisotropic crystal symmetry between the epitaxial films and substrates. In this study, highly enhanced state-of-the-art photoelectrical performance is achieved using single-domain epitaxy of monoclinic β-Ga₂O₃ films on a hexagonal sapphire substrate. Unlike 3D β-Ga₂O₃ films with twin domains, 2D β-Ga₂O₃ films exhibit a single domain with a smooth surface and low concentration of point defects, which enable efficient charge separation by suppressing boundary-induced recombination. Furthermore, a tailored anti-reflection coating (ARC) is adopted as a light-absorbing medium to improve charge generation. The tailored nanostructure, which features a gradient refractive index, not only substantially reduces the reflection, but also suppresses the surface leakage current as a passivation layer. This study provides fundamental insights into the single-domain epitaxy of β-Ga₂O₃ films and the application of ARC for the development of high-performance UVC PDs.

Nature Materials, Published online: 27 October 2023; doi:10.1038/s41563-023-01685-z

By stacking few-layer WSe2 in proximity to twisted double bilayer graphene, researchers report solid evidence of superconductivity.

This study introduces a biosensing device composed of Tin sulfide (SnS₂) and h-BN crystals for streptavidin detection. Researchers incorporate a biotin-based supporter construct conjugated with Pyrene–Lysine, effectively capturing the target analyte. Device performance is validated by Raman spectroscopy and electrical characterizations, which detect 0.5 pm streptavidin in 13.2 s.

Abstract

The exclusive features of two-dimensional (2D) semiconductors, such as high surface-to-volume ratios, tunable electronic properties, and biocompatibility, provide promising opportunities for developing highly sensitive biosensors. However, developing practical biosensors that can promptly detect low concentrations of target analytes remains a challenging task. Here, a field-effect-transistor comprising n-type transition metal dichalcogenide tin disulfide (SnS₂) is developed over the hexagonal boron nitride (h-BN) for the detection of streptavidin protein (Strep.) as a target analyte. A self-designed receptor based on the pyrene-lysine conjugated with biotin (PLCB) is utilized to maintain the sensitivity of the SnS₂/h-BN FET because of the π–π stacking. The detection capabilities of SnS₂/h-BN FET are investigated using both Raman spectroscopy and electrical characterizations. The real-time electrical measurements exhibit that the SnS₂/h-BN FET is capable of detecting streptavidin at a remarkably low concentration of 0.5 pm, within 13.2 s. Additionally, the selectivity of the device is investigated by measuring its response against a Cow-like serum egg white protein (BSA), having a comparative molecular weight to that of the streptavidin. These results indicate a high sensitivity and rapid response of SnS₂/h-BN biosensor against the selective proteins, which can have significant implications in several fields including point-of-care diagnostics, drug discovery, and environmental monitoring.

The magnetization reversal process of a set of nanocomposites with a local texture at the interfaces between SrFe₁₂O₁₉/CoFe₂O₄ is investigated by combining for the first time, remanence (SFD), FORCs [P(Hc)] and relaxation measurements [S(H)]. The results evidence a strong intergranular exchange coupling, and quantify the size limit of the rigid coupling regime in this kind of ferrites.

Abstract

The magnetic coupling of a set of SrFe₁₂O₁₉/CoFe₂O₄ nanocomposites is investigated. Advanced electron microscopy evidences the structural coherence and texture at the interfaces of the nanostructures. The fraction of the lower anisotropy phase (CoFe₂O₄) is tuned to assess the limits that define magnetically exchange-coupled interfaces by performing magnetic remanence, first-order reversal curves (FORCs), and relaxation measurements. By combining these magnetometry techniques and the structural and morphological information from X-ray diffraction, electron microscopy, and Mössbauer spectrometry, the exchange intergranular interaction is evidenced, and the critical thickness within which coupled interfaces have a uniform reversal unraveled.

Miniature piezoelectric robots (MPRs) have exhibited many highlight features and captured considerable attentions and favor of numerous scholars. A comprehensive review of recent development in MPRs is provided, including the operating environment, the structure of piezoelectric actuating element, working principle, attempts of new fabricated methods and piezoelectric materials, and application progresses. The challenges and future trends are evaluated and discussed.

Abstract

Miniature robots have been widely studied and applied in the fields of search and rescue, reconnaissance, micromanipulation, and even the interior of the human body benefiting from their highlight features of small size, light weight, and agile movement. With the development of new smart materials, many functional actuating elements have been proposed to construct miniature robots. Compared with other actuating elements, piezoelectric actuating elements have the advantages of compact structure, high power density, fast response, high resolution, and no electromagnetic interference, which make them greatly suitable for actuating miniature robots, and capture the attentions and favor of numerous scholars. In this paper, a comprehensive review of recent developments in miniature piezoelectric robots (MPRs) is provided. The MPRs are classified and summarized in detail from three aspects of operating environment, structure of piezoelectric actuating element, and working principle. In addition, new manufacturing methods and piezoelectric materials in MPRs, as well as the application situations, are sorted out and outlined. Finally, the challenges and future trends of MPRs are evaluated and discussed. It is hoped that this review will be of great assistance for determining appropriate designs and guiding future developments of MPRs, and provide a destination board to the researchers interested in MPRs.

A universal “all-in-one” blowing strategy, that integrates the carbonization and chalcogenization processes, is developed to fabricate as many as 32 kinds of transition metal chalcogenides/carbon nanosheets composites (termed TMCs@CNS). Both physical and chemical evolution processes have been studied to reveal the blowing mechanism. The highly tunable composition and structure of the products confer on them great promise in diverse fields.

Abstract

Transition metal chalcogenides (TMCs) belongs to the most promising class of materials with unique properties and widespread applications. Coupling with carbon materials allows further enhancement of the specific performance of TMCs by mitigating their intrinsic deficiencies. However, the synthesis of a wide variety of TMCs/carbon composites with a universal strategy especially in a scalable manner remains challenging. In this work, by utilizing the gas-liquid interfaces in viscous gel precursors, an “all-in-one” blowing strategy is proposed to achieve the synchronous growth of TMCs and carbon nanosheets, obviating the additional chalcogenization process. The generality of the proposed blowing strategy is validated by the fabrication of 32 different TMCs/carbon composites, including 24 binary TMCs, 4 ternary TMCs and 4 high-entropy sulfides. In-depth mechanistic study is accomplished by investigating the physical evolution of blowing process and accompanying chemical reactions systematically. Also, the structure of the resulting foam is adjustable by controlling the heating rate and viscosity of the precursors is demonstrated. As an illustrative example for the application of energy storage, MoS_2xSe_2(1-x)@CNS exhibits great Li⁺ storage capacity and cycling stability. Overall, this methodology serves as an effective general strategy for the rational discovery of TMCs/carbon composites and inorganic solid foams.

There is a great prospect for termination-free MXene (MX) in catalysis, energy, and environmental applications. Beyond the currently and widely studied MXene, the termination-free MXs, high-entropy MXs, and MX-supported single atoms enable a huge spectrum of new and unique functional properties for targeted applications, to be developed in the coming few years.

Abstract

The fast ever-growing interest in transition metal carbonitrides (MXenes) for energy and catalysis is undermined by the undesirable multi-surficial terminations, which severely limit their applications. In contrast, considering the intriguing and tunable electronic structure, rich surface active sites, and high thermal durability, termination-free MXene (MX) hosts a huge possibility for catalysis. As such, recent advances in the evolution from MAX to MXene, and then to MX are overviewed and compared briefly, before concentrating on the unique future of MX in multi-heterogeneous catalysis. This work also looks beyond the fundamental properties of MX and discusses the potential of such materials for applications in multi-electron redox reactions. It is convinced that the potential success of MX in future catalysis is promising. Further extension toward high entropy and single-atom modifications will consolidate the leading position of MX in catalysis.

4 in. Cu(111) wafers with ≈95% crystallinity are achieved with the introduction of a temperature gradient on Cu films with designed texture. During the abnormal growth of Cu(111) grain across the whole Cu wafer, in-plane twin boundaries are eliminated via the migration of out-of-plane grain boundaries. Graphene wafers grown on the resulting Cu(111) substrates exhibit improved crystallinity and electrical properties.

Abstract

Single-crystal graphene (SCG) wafers are needed to enable mass-electronics and optoelectronics owing to their excellent properties and compatibility with silicon-based technology. Controlled synthesis of high-quality SCG wafers can be done exploiting single-crystal Cu(111) substrates as epitaxial growth substrates recently. However, current Cu(111) films prepared by magnetron sputtering on single-crystal sapphire wafers still suffer from in-plane twin boundaries, which degrade the SCG chemical vapor deposition. Here, it is shown how to eliminate twin boundaries on Cu and achieve 4 in. Cu(111) wafers with ≈95% crystallinity. The introduction of a temperature gradient on Cu films with designed texture during annealing drives abnormal grain growth across the whole Cu wafer. In-plane twin boundaries are eliminated via migration of out-of-plane grain boundaries. SCG wafers grown on the resulting single-crystal Cu(111) substrates exhibit improved crystallinity with >97% aligned graphene domains. As-synthesized SCG wafers exhibit an average carrier mobility up to 7284 cm² V⁻¹ s⁻¹ at room temperature from 103 devices and a uniform sheet resistance with only 5% deviation in 4 in. region.

As a new approach to “More than Moore”, a stretchable and transparent ionic display module of the integrated ionic circuit is successfully prepared. It is programmed to excite the hydrogel color change by a Faraday process occurring at specific pixel points. The display module exhibits stable performance under strong magnetic field conditions.

Abstract

As a new approach to “More than Moore”, integrated ionic circuits serve as a possible alternative to traditional electronic circuits, yet the integrated ionic circuit composed of functional ionic elements and ionic connections is still challenging. Herein, a stretchable and transparent ionic display module of the integrated ionic circuit has been successfully prepared and demonstrated by pixelating a proton-responsive hydrogel. It is programmed to excite the hydrogel color change by a Faraday process occurring at the electrode at the specific pixel points, which enables the display of digital information and even color information. Importantly, the display module exhibits stable performance under strong magnetic field conditions (1.7 T). The transparent and stretchable nature of such ionic modules also allows them to be utilized in a broad range of scenarios, which paves the way for integrated ionic circuits.

Hexagonal- and tetragonal-2H─PtSe₂ single-crystal flakes are controllably grown. It is found that the higher growth temperature would facilitate the nucleation of PtSe₂ with a-axis orientation, while c-axis PtSe₂ is preferred at lower temperatures. The single-crystal flakes are systematically studied by HRTEM, in situ high-pressure Raman, and polarization Raman. The electrical properties investigations demonstrate structure-correlated electronic and magnetic transport mechanisms.

Abstract

Due to the narrow bandgap, environment stability, and Pt vacancy-induced magnetism, PtSe₂ has been considered a promising candidate for future broadband photodetection and electronics. However, the growth of single-crystal PtSe₂ is still a challenge. Herein, the synthesis of hexagonal and tetragonal 2H─PtSe₂ single-crystal flakes by precisely tailoring the growth temperature is reported. Through atomic structure analysis, hexagonal and tetragonal flakes are proven c-axis and a-axis orientations of 2H─PtSe₂, indicating the preferred nucleation orientations are along the basal plane and vertically basal plane, respectively. The crystalline orientation-dependent properties are studied including high-pressure and polarized in situ-Raman, electrical transport. The out-of-basal plane vibration (A_1g) is sensitive to pressure showing 2.744 and 3.282 cm⁻¹ GPa⁻¹ corresponding to c-2H─PtSe₂ and a-2H─PtSe₂, respectively. The conductivity of c-2H─PtSe₂ is 57 times higher than that of a-2H─PtSe₂. Furthermore, by studying magnetic transport at low temperatures, both c-2H─PtSe₂ and a-2H─PtSe₂ exhibit butterfly-shaped magnetoresistance hysteresis suggesting their ferromagnetic property. The c-2H─PtSe₂ has a higher |MR| ratio and higher coercive field compared with a-2H─PtSe₂, indicating that across multilayer carrier regulation for c-2H─PtSe₂ is more difficult than intra-layer carrier regulation for a-2H─PtSe₂. This study opens the way to grow different crystalline orientations of 2D materials and will bring more abundant properties.

Nature Reviews Methods Primers, Published online: 26 October 2023; doi:10.1038/s43586-023-00263-6

Electrochemical surface-enhanced Raman spectroscopy measurements involve the collection of greatly enhanced Raman spectra at the electrified interface of nanostructured metal surfaces. In this Primer, Brosseau et al. describe the mechanisms of electrochemical surface-enhanced Raman spectroscopy and important experimental details as well as data preprocessing, interpretation and analysis.

Nature Electronics, Published online: 26 October 2023; doi:10.1038/s41928-023-01052-5

Five-stage ring oscillators that operate at frequencies of up to 2.65 GHz can be created using monolayer molybdenum disulfide field-effect transistors developed with a design-technology co-optimization process.

Nature Electronics, Published online: 26 October 2023; doi:10.1038/s41928-023-01050-7

A ternary metallic alloy VS2xSe2(1–x) that has a tunable work function can be grown using chemical vapour deposition and used as contacts for two-dimensional semiconductors.

Optical comb lasers could increase data transmission rates in telecommunications

Sustainability and human health risk are important factors to be considered in developing next-generation device technology. A materials screening protocol that brings in sustainability and safety considerations is proposed. Using ultrawide bandgap 2D materials as a backdrop, 25 candidates comprising only of low-risks elements are identified. Their potential in gate dielectric, power electronics, and ultraviolet photonics applications are demonstrated.

Abstract

The sustainable development of next-generation device technology is paramount in the face of climate change and the looming energy crisis. Tremendous effort is made in the discovery and design of nanomaterials that achieve device-level sustainability, where high performance and low operational energy cost are prioritized. However, many of such materials are composed of elements that are under threat of depletion and pose elevated risks to the environment and human health. The role of materials-level sustainability in computational screening efforts is overlooked thus far. This work presents a general van der Waals materials screening framework imbued with sustainability-motivated search criteria. Using ultrawide bandgap (UWBG) materials as a backdrop, 25 sustainable UWBG layered materials comprising only of low-risks elements result from this screening effort, with several meeting the requirements for dielectric, power electronics, and ultraviolet device applications. These findings constitute a critical first-step toward reinventing a more sustainable electronics landscape beyond silicon, with the framework established in this work serving as a harbinger of sustainable 2D materials discovery.

Nature, Published online: 25 October 2023; doi:10.1038/s41586-023-06530-6

Some of the diffuse intensities observed in electron diffraction patterns of face-centred cubic multi-principal element alloys are due to reflections from higher-order Laue zones.

Proceedings of the National Academy of Sciences, Volume 120, Issue 45, November 2023.