Jiuxiang Dai

The search for high-mobility, low-dimensional magnets are usually confined within van der Waals materials. However, their structural clues suggest that these features can also be found in other layered materials with relatively stronger interlayer coupling. Bulk NdSb₂ is presented as a typical example which shows quasi 2D electronic and magnetic properties and can be exfoliated down to few-layer thickness.

Abstract

Advancements in low-dimensional functional device technology heavily rely on the discovery of suitable materials which have interesting physical properties as well as can be exfoliated down to the 2D limit. Exfoliable high-mobility magnets are one such class of materials that, not due to lack of effort, has been limited to only a handful of options. So far, most of the attention has been focused on the van der Waals (vdW) systems. However, even within the non-vdW, layered materials, it is possible to find all these desirable features. Using chemical reasoning, it is found that NdSb₂ is an ideal example. Even with a relatively small interlayer distance, this material can be exfoliated down to few layers. NdSb₂ has an antiferromagnetic ground state with a quasi 2D spin arrangement. The bulk crystals show a very large, non-saturating magnetoresistance along with highly anisotropic electronic transport properties. It is confirmed that this anisotropy originates from the 2D Fermi pockets which also imply a rather quasi 2D confinement of the charge carrier density. Both electron and hole-type carriers show very high mobilities. The possible non-collinear spin arrangement also results in an anomalous Hall effect.

QD-Polymer composites for direct photolithography are of great significance to the development of today's display technology. This review presents representative design strategies for QD-Polymer that can be used for direct photolithography and the development of the direct photolithography process for de-photomasking, which provides guidance for advancing QD-Polymer for high-quality patterning and display applications.

Abstract

For the new display technology based on quantum dots (QDs), achieving high-precision red, green, and blue pixel arrays has always been a research focus in the pursuit of high-quality and vivid image displays. However, problems such as material stability and process environment make it difficult to guarantee the quality of high-precision patterns. The new optical patterning technology represented by direct photolithography is considered a highly promising method for achieving ultrafine patterns at the submicron level. This process prepares patterned quantum dot-polymer films through light-induced chemical changes. This paper reviews the progress of direct photolithography research focused on QD-polymer materials and presents recent advances in such processes for monochromatic/multicolor light patterning. The article classifies QD-polymers into three categories by combining QDs with polymers in different ways, including polymer-coated QDs, polymers as QD ligands, and polymers as photocrosslinkers for QDs. Their synthesis schemes, functional features, and challenges are also presented. In addition, a scheme to remove the photomask during direct lithography using lasers and light field modulation is also proposed. It aims to provide readers and researchers with some generalized research information and improvement ideas. This can further advance the development of direct photolithography for QD-polymers.

Oxide and halide perovskites play a key role in various energy conversion devices such as piezoelectric devices, catalysts, light emitting diodes, and photodetectors. This review covers the latest studies on strain engineering in both oxide and halide perovskites for energy conversion devices. The work provides a new insight that can lead breakthroughs for high performance energy conversion devices.

Abstract

Perovskite materials have garnered significant attention over the past decades due to their applications, not only in electronic materials, such as dielectrics, piezoelectrics, ferroelectrics, and superconductors but also in optoelectronic devices like solar cells and light emitting diodes. This interest arises from their versatile combinations and physiochemical tunability. While strain engineering is a recognized powerful tool for tailoring material properties, its collaborative impact on both oxides and halides remains understudied. Herein, strain engineering in perovskites for energy conversion devices, providing mutual insight into both oxides and halides is discussed. The various experimental methods are presented for applying strain by using thermal mismatch, lattice mismatch, defects, doping, light illumination, and flexible substrates. In addition, the main factors that are influenced by strain, categorized as structure (e.g., symmetry breaking, octahedral distortion), bandgap, chemical reactivity, and defect formation energy are described. After that, recent progress in strain engineering for perovskite oxides and halides for energy conversion devices is introduced. Promising methods for enhancing the performance of energy conversion devices using perovskites through strain engineering are suggested.

Abstract

The van der Waals heterostructures have evolved as novel materials for complementing the Si-based semiconductor technologies. Group-10 noble metal dichalcogenides (e.g., PtS₂, PtSe₂, PdS₂, and PdSe₂) have been listed into two-dimensional (2D) materials toolkit to assemble van der Waals heterostructures. Among them, PdSe₂ demonstrates advantages of high stability in air, high mobility, and wide tunable bandgap. However, the regulation of p-type doping of PdSe₂ remains unsolved problem prior to fabricating p–n junction as a fundamental platform of semiconductor physics. Besides, a quantitative method for the controllable doping of PdSe₂ is yet to be reported. In this study, the doping level of PdSe₂ was correlated with the concentration of Lewis acids, for example, SnCl₄, used for soaking. Considering the transfer characteristics, the threshold voltage (the gate voltage corresponding to the minimum drain current) increased after SnCl₄ soaking treatment. PdSe₂ transistors were soaked in SnCl₄ solutions with five different concentrations. The threshold voltages from the as-obtained transfer curves were extracted for linear fitting to the threshold voltage versus doping concentration correlation equation. This study provides in-depth insights into the controllable p-type doping of PdSe₂. It may also push forward the research of the regulation of conductivity behaviors of 2D materials.

Nature Synthesis, Published online: 27 November 2023; doi:10.1038/s44160-023-00442-z

Nature Communications, Published online: 27 November 2023; doi:10.1038/s41467-023-43340-w

This work reports on a novel bottom–up approach, using three atom-long tellurium chains, derived from the dynamic non-equilibrium growth of an a-Si:Te alloy, as building blocks for the self-assembly of monolayer α-tellurene on a Sb₂Te₃ substrate. Atomic-resolution scanning tunneling microscopy demonstrates the hexagonal lattice of α-tellurene.

Abstract

2D materials emerge as a versatile platform for developing next-generation devices. The experimental realization of novel artificial 2D atomic crystals, which does not have bulk counterparts in nature, is still challenging and always requires new physical or chemical processes. Monolayer α-tellurene is predicted to be a stable 2D allotrope of tellurium (Te), which has great potential for applications in high-performance field-effect transistors. However, the synthesis of monolayer α-tellurene remains elusive because of its complex lattice configuration, in which the Te atoms are stacked in tri-layers in an octahedral fashion. Here, a self-assemble approach, using three atom-long Te chains derived from the dynamic non-equilibrium growth of an a-Si:Te alloy as building blocks, is reported for the epitaxial growth of monolayer α-tellurene on a Sb₂Te₃ substrate. By combining scanning tunneling microscopy/spectroscopy with density functional theory calculations, the surface morphology and electronic structure of monolayer α-tellurene are revealed and the underlying growth mechanism is determined. The successful synthesis of monolayer α-tellurene opens up the possibility for the application of this new single-element 2D material in advanced electronic devices.

Nature Protocols, Published online: 27 November 2023; doi:10.1038/s41596-023-00911-x

The combination of the low thickness of a 2D material and the magnetic properties of a ferromagnetic element holds great promise for the formation of materials with diverse characteristics applicable in spintronics and multiple other fields. Furthermore, a ferromagnetic element, through the proximity effect, can convert 2D materials into 2D magnets by providing long-lasting magnetic properties.

Abstract

Ferromagnetism in 2D materials has attracted tremendous interest from the scientific community thanks to its potential for the design of magnetic materials with unique properties. The presence of a ferromagnetic element in a 2D material can improve the existing properties and offer new ones, giving rise to the development of manifold applications. This review focuses on recent advances and perspectives of 2D materials that bear at least one ferromagnetic element (iron, cobalt, nickel) as i) structural constituent, ii) dopant atom, or iii) adjacent atom through proximity effect. By describing in detail the magnetic properties that have emerged so far, their potential to form next-generation 2D magnets is discussed. Moreover, the contribution of such 2D materials is analyzed in various applications (electrochemical, photochemical, optical, and electronic), aiming to explore further functionalities and capabilities of ferromagnetic elements, apart from their magnetic nature. Special attention is given to gadolinium and other rare earth elements that display a ferromagnetic order even at ultra-low temperatures and form part of 2D structured materials, with particularly appealing properties deriving from their 4f electrons.

A 2D Bi₂O₂Se/CsBi₃I₁₀ perovskite heterojunction for highly-sensitive and broadband photodetector is demonstrated. The effective interfacial charge transfer and strong coupling effect between CsBi₃I₁₀ and Bi₂O₂Se accelerate the photodetector response time to 4.1 µs, and also expand the photodetection ranging from ultraviolet to near-infrared regions (300-1500 nm).

Abstract

2D Bi₂O₂Se has recently garnered significant attention in the electronics and optoelectronics fields due to its remarkable photosensitivity, broad spectral absorption, and excellent long-term environmental stability. However, the development of integrated Bi₂O₂Se photodetector with high performance and low-power consumption is limited by material synthesis method and the inherent high carrier concentration of Bi₂O₂Se. Here, a type-I heterojunction is presented, comprising 2D Bi₂O₂Se and lead-free bismuth perovskite CsBi₃I₁₀, for fast response and broadband detection. Through effective charge transfer and strong coupling effect at the interfaces of Bi₂O₂Se and CsBi₃I₁₀, the response time is accelerated to 4.1 µs, and the detection range is expanded from ultraviolet to near-infrared spectral regions (365–1500 nm). The as-fabricated photodetector exhibits a responsivity of 48.63 AW⁻¹ and a detectivity of 1.22×10¹² Jones at 808 nm. Moreover, efficient modulation of the dominant photocurrent generation mechanism from photoconductive to photogating effect leads to sensitive response exceeding 10³ AW⁻¹ for heterojunction-based photo field effect transistor (photo-FETs). Utilizing the large-scale growth of both Bi₂O₂Se and CsBi₃I₁₀, the as-fabricated integrated photodetector array demonstrates outstanding homogeneity and stability of photo-response performance. The proposed 2D Bi₂O₂Se/CsBi₃I₁₀ perovskite heterojunction holds promising prospects for the future-generation photodetector arrays and integrated optoelectronic systems.

The amorphous Ti₂C–MXene model has a unique amorphous structure. The amorphous Ti₂C composited by [Ti₅C] and [Ti₆C] cluster, which are surrounded by the region of mixed cluster [Ti _x C], [Ti–Ti] cluster and [C–C] cluster. The amorphous Ti₂C–MXene exhibit higher activity for boosting hydrogen evolution reaction performance. The work provides insights that can pave the way for future research on novel MXenes.

Abstract

The emergence of amorphous 2D materials has opened up new avenue for materials science and nanotechnology in the recent years. Their unique disordered structure, excellent large-area uniformity, and low fabrication cost make them important for various industrial applications. However, there have no reports on the amorphous MXene materials. In this work, the amorphous Ti₂C–MXene (a-Ti₂C–MXene) model is built by ab initio molecular dynamics (AIMD) approach. This model is a unique amorphous model, which is totally different from continuous random network (CRN) model for silicate glass and amorphous model for amorphous 2D BN and graphene. The structure analysis shows that the a-Ti₂C–MXene composited by [Ti₅C] and [Ti₆C] cluster, which are surrounded by the region of mixed cluster [Ti _x C], [Ti–Ti] cluster, and [C–C] cluster. There is a high chemical activity for hydrogen evolution reaction (HER) in a-Ti₂C–MXene with |ΔG _H| 0.001 eV, implying that they serve as the potential boosting HER performance. The work provides insights that can pave the way for future research on novel MXene materials, leading to their increased applications in various fields.

Chiral photonic cellulose nanocrystals films displaying pearlescence, iridescence and specular reflection are organized. The film's optical appearance can be readily tuned with the architectural design and can be used for anti-counterfeiting applications. It marks the beginning of chiral pearlescent materials, while pressure-directed self-assembly enables reproducible optical properties with high fidelity.

Abstract

Pearlescent materials are of technological importance in a diverse array of industries from cosmetics to premium paints; however, chiral pearlescent materials remain unexplored. Here, chiral pearlescent films with on-demand iridescence and metallic appearance are simply organized by leveraging vertical pressure to direct the self-assembly of cellulose nanocrystals. The films are formed with a bilayer planar anchored left-handed chiral nematic architecture, in which the bottom layer is featured with a vertical gradient pitch, and the top layer is featured with a uniform pitch. Simultaneous reflection of the rainbow colors and an on-demand color of left-handed polarized light with angle-dependent wavelength and polarization state accounts for the unique optical phenomenon based on experimental observation and theoretical analysis. Such chiroptical property can be readily tuned with architectural design, enabling reproducible optical appearance with high fidelity. Bringing the pearlescence, iridescence, and specular reflection together endows cellulose nanocrystal films with rich and tunable chiroptical properties that can be used for anti-counterfeiting applications. The current work marks the beginning of chiral pearlescent materials from renewable resources, while the pressure-directed self-assembly provides a step toward scalable production.

Controlling the electric and optical properties of WS₂ monolayers via intentional defect inclusion is an effective way to mitigate the intrinsic defect issue and tailor the material properties. This work provides a systematic analysis of defects in WS₂, considering both intrinsic defects and different, innovative doping schemes, reporting a combination of theoretical and experimental evidence.

Abstract

Two-dimensional (2D) materials as tungsten disulphide (WS₂) are rising as the ideal platform for the next generation of nanoscale devices due to the excellent electric-transport and optical properties. However, the presence of defects in the as grown samples represents one of the main limiting factors for commercial applications. At the same time, WS₂ properties are frequently tailored by introducing impurities at specific sites. Aim of this review paper is to present a complete description and discussion of the effects of both intentional and unintentional defects in WS₂, by an in depth analysis of the recent experimental and theoretical investigations reported in the literature. First, the most frequent intrinsic defects in WS₂ are presented and their effects in the readily synthetized material are discussed. Possible solutions to remove and heal unintentional defects are also analyzed. Following, different doping schemes are reported, including the traditional substitution approach and innovative techniques based on the surface charge transfer with adsorbed atoms or molecules. The plethora of WS₂ monolayer modifications presented in this review and the systematic analysis of the corresponding optical and electronic properties, represent strategic degrees of freedom the researchers may exploit to tailor WS₂ optical and electronic properties for specific device applications.

The multipurpose solar-blind ultraviolet photodetectors based on p-PCDTBT/n-Ga₂O₃ heterojunction and capable of working in phototransistor mode coupled with self-powered mode are realized in this study. The phototransistor shows an outstanding response to solar-blind UV light in all modes, which provides the avenue for the further applications of amorphous Ga₂O₃-based photodetectors.

Abstract

Solar-blind ultraviolet (UV) photodetectors based on p-organic/n-Ga₂O₃ hybrid heterojunctions have attracted extensive attention recently. Herein, the multifunctional solar-blind photodetector based on p-type poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT)/n-type amorphous Ga₂O₃ (a-Ga₂O₃) is fabricated and investigated, which can work in the phototransistor mode coupling with self-powered mode. With the introduction of PCDTBT, the dark current of such the a-Ga₂O₃-based photodetector is decreased to 0.48 pA. Meanwhile, the photoresponse parameters of the a-Ga₂O₃-based photodetector in the phototransistor mode to solar-blind UV light are further increased, that is, responsivity (R), photo-detectivity (D*), and external quantum efficiency (EQE) enhanced to 187 A W^–1, 1.3 × 10¹⁶ Jones and 9.1 × 10⁴ % under the weak light intensity of 11 μW cm^{– 2}, respectively. Thanks to the formation of the built-in field in the p-PCDTBT/n-Ga₂O₃ type-II heterojunction, the PCDTBT/Ga₂O₃ multifunctional photodetector shows self-powered behavior. The responsivity of p-PCDTBT/n-Ga₂O₃ multifunctional photodetector is 57.5 mA W^–1 at zero bias. Such multifunctional p-n hybrid heterojunction-based photodetectors set the stage for realizing high-performance amorphous Ga₂O₃ heterojunction-based photodetectors.

Nature Electronics, Published online: 22 November 2023; doi:10.1038/s41928-023-01043-6

Erbium (Er)-doped III-V semiconductors are promising for optoelectronic devices due to the unique intra-4f electronic transitions of Er³⁺. This work reports the Er-related photoluminescence from near ultraviolet to near-infrared in ErAs:GaAs grown by molecular beam epitaxy. A carrier-mediated energy transfer up-conversion mechanism is proposed, and the excited-state absorption is confirmed to be governed by a single photonic process.

Abstract

Erbium (Er)-doped III-V semiconductors are promising for optoelectronic devices due to the unique intra-4f electronic transitions of Er³⁺; however, the Er-related luminescence at room temperature has always been challenging to obtain. In this work, High crystalline quality ErAs:GaAs films are grown with self-assembled ErAs nanoparticles embedded within the GaAs matrix by molecular beam epitaxy. Rich photoluminescence spectra in a broad wavelength ranging from near-ultraviolet to near-infrared are observed at room temperature and confirmed to be Er-related. A carrier-mediated energy transfer up-conversion mechanism is proposed, and the pump power-dependent photoluminescence results reveal that the excited-state absorption is governed by a single photonic process. The efficient interaction and energy transfer between the semiconductor matrix and Er³⁺ ions offered by this unique nanocomposite material provide a promising route to achieve novel optoelectronic devices with the potential to cover a broad wavelength range.

In this article, optical coupling of monolayer transition metal dichalcogenides (TMDs) to hexagonal boron nitride (hBN) slab waveguides is studied. The hBN encapsulation provides a pristine dielectric environment around the TMD, while simultaneously providing optical access via waveguiding. The work comprises combined experimental and theoretical approaches, offering essential details necessary to leverage hBN slab waveguides in future research and applications.

Abstract

The layered insulator hexagonal boron nitride (hBN) is a critical substrate that brings out the exceptional intrinsic properties of two-dimensional (2D) materials such as graphene and transition metal dichalcogenides (TMDs). In this work, the authors demonstrate how hBN slabs tuned to the correct thickness act as optical waveguides, enabling direct optical coupling of light emission from encapsulated layers into waveguide modes. Molybdenum selenide (MoSe₂) and tungsten selenide (WSe₂) are integrated within hBN-based waveguides and demonstrate direct coupling of photoluminescence emitted by in-plane and out-of-plane transition dipoles (bright and dark excitons) to slab waveguide modes. Fourier plane imaging of waveguided photoluminescence from MoSe₂ demonstrates that dry etched hBN edges are an effective out-coupler of waveguided light without the need for oil-immersion optics. Gated photoluminescence of WSe₂ demonstrates the ability of hBN waveguides to collect light emitted by out-of-plane dark excitons.Numerical simulations explore the parameters of dipole placement and slab thickness, elucidating the critical design parameters and serving as a guide for novel devices implementing hBN slab waveguides. The results provide a direct route for waveguide-based interrogation of layered materials, as well as a way to integrate layered materials into future photonic devices at arbitrary positions whilst maintaining their intrinsic properties.

We report a small aqueous-soluble lanthanide antenna (PAnt) specifically designed to dynamically interact with lanthanide ions and act as an exchangeable dye, aiming at mitigating photobleaching in PLIM microscopy in cellulo. Our self-assembled lanthanide complex exhibited an exceptional photostability compared to traditional lanthanide cryptates, marking a significant advance in quantitative PLIM bioimaging.

Abstract

Lanthanides have unique photoluminescence (PL) emission properties, including very long PL lifetimes. This makes them ideal for biological imaging applications, especially using PL lifetime imaging microscopy (PLIM). PLIM is an inherently multidimensional technique with exceptional advantages for quantitative biological imaging. Unfortunately, due to the required prolonged acquisitions times, photobleaching of lanthanide PL emission currently constitutes one of the main drawbacks of PLIM. In this study, we report a small aqueous-soluble, lanthanide antenna, 8-methoxy-2-oxo-1,2,4,5-tetrahydrocyclopenta[de]quinoline-3-phosphonic acid, PAnt, specifically designed to dynamically interact with lanthanide ions, serving as exchangeable dye aimed at mitigating photobleaching in PLIM microscopy in cellulo. Thus, self-assembled lanthanide complexes that may be photobleached during image acquisition are continuously replenished by intact lanthanide antennas from a large reservoir. Remarkably, our self-assembled lanthanide complex clearly demonstrated a significant reduction of PL photobleaching when compared to well-established lanthanide cryptates, used for bioimaging. This concept of exchangeable lanthanide antennas opens new possibilities for quantitative PLIM bioimaging.

The complete synthetic process of (Cr, Mn, Fe, Co, and Ni)₃O₄ is observed at the atomic scale. The order of synthetic reactions is thought to be affected by the similarity in crystal structures and lattice constants of the precursor materials. These findings offer valuable insights to enhance the manufacturing process of (Cr, Mn, Fe, Co, and Ni)₃O₄, a crucial development for future lithium-ion batteries' anode materials.

Abstract

High-entropy oxides (HEOs) are promising anode materials for lithium-ion batteries (LIBs), owing to their stable crystal structure, superionic conductivity, and high capacity. In this study, the (Cr, Mn, Fe, Co, and Ni)₃O₄ HEO via solid-state reaction is prepared. To improve the synthetic efficiency, it is necessary to understand the formation mechanism. Therefore, a high-resolution transmission electron microscopy (HRTEM) is used to record information during calcination at increasing temperature. The overall formation process included MnO₂ and NiO aggregation at 500 °C, followed by (Mn, and Ni)₃O₄ combined with Co₃O₄ at 600 °C to form (Mn, Co, and Ni)₃O₄. At higher temperatures, Fe₂O₃ and Cr₂O₃ sequentially combined with (Mn, Co, and Ni)₃O₄ and formed the (Cr, Mn, Fe, Co, Ni)₃O₄ at 900 °C. In addition, the valence-state-changing mechanisms and ion arrangements of (Cr, Mn, Fe, Co, and Ni)₃O₄ are determined using electron energy loss spectroscopy (EELS) and extended X-ray absorption fine structure (EXAFS). This study successfully revealed the formation of HEO at atomic scale. The results provide valuable insights for improving the manufacturing process of (Cr, Mn, Fe, Co, and Ni)₃O₄ HEOs, which is expected to play a vital role in the development of anode materials for next-generation LIBs.

Homogeneous amorphous/crystalline heterophase materials derive advantages from the similar work function properties of the heterophase counterpart and the well-matched Fermi level at the heterophase interface. The facilitated movement of charge carriers within the material, induced by the external electromagnetic field, amplifies the dielectric loss capacity. Consequently, this material demonstrates a remarkably significant minimum reflection loss of −89.5 dB, along with an expanded effective absorption bandwidth of 6.45 GHz.

Abstract

To design and develop efficient microwave absorbents via phase engineering is still less studied. The unique properties caused by constructing heterophase structure hold the potential to strengthen absorbing capability toward microwave radiation. Herein, amorphous/crystalline γ-Fe₂O₃ nanosheets (Fe-H) are carefully fabricated through a controlled annealing process. The matched Fermi levels formed on both sides of the heterophase interface not only provides efficient interfacial polarizations but also facilitates the transport of electrons with less scattering over the whole Fe-H nanosheets. Thereby, both of the conduction loss and dielectric polarization relaxation are promoted, leading to a strengthened attenuation toward electromagnetic wave radiation. The as-synthesized Fe-H sample exhibited a minimum reflection loss of -89.5 dB centered at a thickness of 2.00 mm, associated with an effective absorption bandwidth (reflection loss ≤ -10 dB) reaching 6.45 GHz. All of these behaviors are superior to its pure amorphous absorbent and bare crystalline counterpart. Furthermore, this heterophase engineering strategy is valid when extended to Co and Ni based oxides, suggesting its universality and generality for promoting microwave absorption. Henceforth, this study indicates a favorable potential of the synthesis and application of amorphous/crystalline materials as heterophase microwave absorbents.

Highlights

• A systematic summary of current research trends in the development of transition metal disulfides (TMDs) electromagnetic wave (EMW) absorption materials.

• In-depth comparisons on the structures, preparation methods, application merits of VIB- and VB-group TMDs.

• Structure engineering modulation of TMDs in achieving superior EMW absorption is outlined from the viewpoints of heterostructures, defects, morphologies, and phases.

• Exclusive insights into the challenges, strategies, and opportunities in the design of EMW absorption materials with outstanding performance are provided.

Nature Nanotechnology, Published online: 23 November 2023; doi:10.1038/s41565-023-01558-1

Nature Electronics, Published online: 23 November 2023; doi:10.1038/s41928-023-01071-2

Light: Science & Applications, Published online: 24 November 2023; doi:10.1038/s41377-023-01320-1