Jiuxiang Dai

Excitonic resonance in atomically thin semiconductors has the potential to enable highly tunable and ultra-compact optical devices. However, insufficient light-matter interactions have hindered the observation of trionic phenomenon and the development of excitonic devices for dynamic applications. To overcome this limitation, an optical cavity is engaged, resulting in greatly enhanced exciton-trion conversion at room temperature and enabling both amplitude and phase tuning in monolayer tungsten disulfide.

Abstract

Excitonic resonance in atomically thin semiconductors offers a favorite platform to study 2D nanophotonics in both classical and quantum regimes and promises potentials for highly tunable and ultra-compact optical devices. The understanding of charge density dependent exciton-trion conversion is the key for revealing the underlaying physics of optical tunability. Nevertheless, the insufficient and inefficient light-matter interactions hinder the observation of trionic phenomenon and the development of excitonic devices for dynamic power-efficient electro-optical applications. Here, by engaging an optical cavity with atomically thin transition metal dichalcogenides (TMDCs), greatly enhanced exciton-trion conversion is demonstrated at room temperature (RT) and achieve electrical modulation of reflectivity of ≈40% at exciton and 7% at trion state, which correspondingly enables a broadband large phase tuning in monolayer tungsten disulfide. Besides the absorptive conversion, ≈100% photoluminescence conversion from excitons to trions is observed at RT, illustrating a clear physical mechanism of an efficient exciton-trion conversion for extraordinary optical performance. The results indicate that both excitons and trions can play significant roles in electrical modulation of the optical parameters of TMDCs at RT. The work shows the real possibility for realizing electrical tunable and multi-functional ultra-thin optical devices using 2D materials.

Viable and general method that allows an effective synthesis of transition metal dichalcogenides (TMDs)-O-doped graphene heterostructures by utilizing commercial TMD powder and sucrose as precursors is reported for the first time. The solar evaporators of WS₂-O-graphene exhibit high-performance water evaporation due to the improved photo-excited carrier transportation. This study provides a general approach to prepare diverse heterostructure materials for solar-driven steam evaporation.

Abstract

Two-dimensional (2D) transition metal dichalcogenides and graphene have revealed promising applications in optoelectronic and energy storage and conversion. However, there are rare reports of modifying the light-to-heat transformation via preparing their heterostructures for solar steam generation. In this work, commercial WS₂ and sucrose are utilized as precursors to produce 2D WS₂-O-doped-graphene heterostructures (WS₂-O-graphene) for solar water evaporation. The WS₂-O-graphene evaporators demonstrate excellent average water evaporation rate (2.11 kg m⁻² h⁻¹) and energy efficiency (82.2%), which are 1.3- and 1.2-fold higher than WS₂ and O-doped graphene-based evaporators, respectively. Furthermore, for the real seawater with different pH values (pH 1 and 12) and rhodamine B pollutants, the WS₂-O-graphene evaporators show great average evaporation rates (≈2.08 and 2.09 kg m⁻² h⁻¹, respectively) for producing freshwater with an extremely low-grade of dye residual and nearly neutral pH values. More interestingly, due to the self-storage water ability of WS₂-O-graphene evaporators, water evaporation can be implemented without the presence of bulk water. As a result, the evaporation rate reaches 3.23 kg m⁻² h⁻¹, which is ≈1.5 times higher than the regular solar water evaporation system. This work provides a new approach for preparing 2D transition metal dichalcogenides and graphene heterostructures for efficient solar water evaporation.

In this work, a new and simple strategy of molten salt-assisted synthesis is proposed to enhance lanthanide upconversion luminescence for the first time, which has multiple distinct advantages and is universal for enhancing luminescence. Additionally, the reasons for luminescence enhancement are clearly explained. Furthermore, NIR excitation upconversion white LED was successfully fabricated by using luminescence-enhanced lanthanide upconversion materials.

Abstract

Lanthanide-doped upconversion luminescent materials (LUCMs) have attracted much attention in diverse practical applications because of their superior features. However, the relatively weak luminescence intensity and low efficiency of LUCMs are the bottleneck problems that seriously limit their development. Unfortunately, most of the current major strategies of luminescence enhancement have some inherent shortcomings in their implementation. Here, a new and simple strategy of molten salt-assisted synthesis is proposed to enhance lanthanide upconversion luminescence for the first time. As a proof-of-concept, a series of rare earth oxides with obvious luminescence enhancement are prepared by a one-step method, utilizing molten NaCl as the high-temperature reaction media and rare earth chlorides as the precursors. The enhancement factors at different reaction temperatures are systematically investigated by taking Yb³⁺/Er³⁺ co-doped Y₂O₃ as an example, which can be enhanced up to more than six times. In addition, the molten salts are extended to all alkali chlorides, indicating that it is a universal strategy. Finally, the potential application of obtained UCL materials is demonstrated in near-infrared excited upconversion white light-emitting diodes (WLEDs) and other monochromatic LEDs.

Cuprous oxide/amorphous zinc-tin oxide thin film heterojunction diodes fabricated at room temperature are characterized using capacitance–voltage (C–V) analysis which nicely complements the widely used current–voltage analyses. Doping density can be extracted via the C–V method, showing that the surface accumulation layer can be effectively suppressed by plasma treatments, thus improving the performance of the rectifying junction and the diode.

Abstract

High quality thin film p-n junction diodes with high rectification ratios and low ideality factors have been fabricated from metal oxides, such as amorphous oxide semiconductors (AOSs), and characterized. Plasma treatment of interfaces has been demonstrated to improve devices made from AOSs, using current–voltage (I–V) measurements. However, capacitance–voltage (C–V) measurements of the devices have been scarcely reported in the literature. Therefore, the focus of this work is characterization of cuprous oxide (Cu₂O)/amorphous zinc-tin oxide (a-ZTO) thin film heterojunction diodes using C–V analysis. Performance differences of plasma-treated and untreated diodes that are difficult to observe in I–V analysis are more prominent in C–V analysis. Moreover, C–V analysis allows extraction of charge density profiles, which is a measure of the defect state density that led to intrinsic doping. The variation of doping densities of the untreated diode across the full range of applied reverse bias is shown to be up to 2 orders of magnitude, while those of the treated diodes are within a factor of 10 only. Junction charge profiles, interfacial charge depletion, and accumulation that are key features of rectifying diodes are shown to be clearly distinct between untreated, nitrogen-treated, and oxygen-treated diodes, thus explaining why oxygen-treated diodes are superior.

One of the thermal transport and thermoelectric applications requires unambiguous characterization of the thermal transport anisotropy. Here, a potent methodology for direct measurements of nanoscale anisotropic and interfacial heat transport of a promising vdW thermoelectric crystal (InSe) is reported, finding anomalously low and anisotropic thermal conductivity.

Abstract

Van der Waals (vdW) atomically thin materials and their heterostructures offer a versatile platform for the management of nanoscale heat transport and the design of novel thermoelectrics. These require the measurement of highly anisotropic heat transport in vdW-based nanolayers, a major challenge for nanostructured materials and devices. In the present study, a novel effective method of cross-sectional scanning thermal microscopy was used to map and quantify the anisotropic heat transport in nanoscale thick layers of vdW materials and the material-substrate interfaces. This technique measures the heat conducted into a vdW crystal via the nanoscale apex of a heat-sensitive probe. The crystal is nano-polished via Ar ion beams generating an oblique nearly atomically flat surface. By measuring the thermal conductance variation as a function of increasing layer thickness, the transition between the cross-plane and in-plane heat transport (defined by heat conductivity anisotropy) is acquired. By using an analytical model validated by finite element simulations, anisotropic thermal transport in a gamma indium selenide crystal nano-thin flake on a Si substrate was studied, obtaining results corresponding to anomalously low anisotropic thermal conductivities of k _xy = 2.16 Wm⁻¹ K⁻¹ in-plane and k _z = 0.89 Wm⁻¹ K⁻¹ cross-plane confirming its potential for thermoelectric applications.

Light: Science & Applications, Published online: 12 May 2023; doi:10.1038/s41377-023-01171-w

Localized moiré excitons were found in twisted heterotrilayer superlattices, with the moiré potential depth tunable through layer degrees of freedom. This discovery benefits quantum light emitter development.

Accordion-like metal-bonded transition metal carbides (MXenes) are produced through a topological reaction between Cl-terminated MXenes and selected metals, which is driven by the crystal symmetry of the MAX phases. After the delamination and assembling, the films composed of Al-bonded Ti₃C₂Cl_x MXene atomic layers exhibit high oxidation resistance and low sheet resistances, affording a significantly enhanced property in electromagnetic interference (EMI) sheilding.

Abstract

Although 2D transition metal carbides and nitrides (MXenes) have fantastic physical and chemical properties as well as wide applications, it remains challenging to produce stable MXenes due to their rapid structural degradation. Here, unique metal-bonded atomic layers of transition metal carbides with high stabilities are produced via a simple topological reaction between chlorine-terminated MXenes and selected metals, where the metals enable them to not only remove partially Cl terminations, but also bond with adjacent atomic MXene slabs, driven by the symmetry of MAX phases. The films constructed from Al-bonded Ti₃C₂Cl_x atomic layers show high oxidation resistance up to 400 °C and low sheet resistance of 9.3 Ω sq⁻¹. Coupled to the multilayer structure, the Al-bonded Ti₃C₂Cl_x film displays a significantly improved electromagnetic interference (EMI) shielding capability with a total shielding effectiveness value of 39 dB at a low thickness of 3.1 µm, outperforming pure Ti₃C₂Cl_x film.

Complex oxides, where various order parameters in electrons are strongly correlated, are an excellent platform for exploring exotic physical phenomena and for developing multi-functional devices. In complex oxide thin-film heterostructures, intrinsic and extrinsic polar elements, which are inherently and externally applicable to perturb physical properties, respectively, enable the realization of emerging functionalities which are usually inaccessible in nature.

Abstract

Growth and characterization of metal-oxide thin films foster successful development of oxide-material-integrated thin-film devices represented by metal-oxide-semiconductor field-effect transistors (MOSFET), drawing enormous technological and scientific interest for several decades. In recent years, functional oxide heterostructures have demonstrated remarkable achievements in modern technologies and provided deeper insights into condensed-matter physics and materials science owing to their versatile tunability and selective amplification of the functionalities. One of the most critical aspects of their physical properties is the polar perturbation stemming from the ionic framework of an oxide. By engineering and exploiting the structural, electrical, magnetic, and optical characteristics through various routes, numerous perceptive studies have clearly shown how polar perturbations advance functionalities or drive exotic physical phenomena in complex oxide heterostructures. In this review, both intrinsic (engraved by thin-film heteroepitaxy) and extrinsic (reversibly controllable defect-mediated disorder and polar adsorbates) elements of polar perturbations, highlighting their abilities for the development of highly tunable functional properties are summarized. Scientifically, the recent approaches of polar perturbations render one to consolidate a prospect of atomic-level manipulation of polar order in epitaxial oxide thin films. Technologically, this review also offers useful guidelines for rational design to heterogeneously integrated oxide-based multi-functional devices with high performances.

Information Storage

In article number 2213668, Ming Liu, Bin Peng, and co-workers introduce a self-assembly method to fabricate scroll-like 3D architecture, which can increase the information storage density in ferroelectric memories. It is enabled by the self-rolling-up of freestanding single-crystalline ferroic oxide membranes. The information storage density could be enhanced at least one order of magnitude (experimentally 45.7 times) and 100–450 times (theoretically) than planar thin films.

GaP nanowire optical properties are studied in detail to demonstrate the pathways for fabrication of low-loss and subwavelength waveguides for visible and near-infrared ranges. The nanowires exhibit perfect elasticity and stable waveguiding demonstrated via fabrication of an optical X-coupler. The results of the work unveil feasibility for GaP nanowires implementation as elements of advanced photonic schemes.

Abstract

Emerging technologies for integrated optical circuits demand novel approaches and materials. This includes a search for nanoscale waveguides that should satisfy criteria of high optical density, small cross-section, technological feasibility and structural perfection. All these criteria are met with self-assembled gallium phosphide (GaP) epitaxial nanowires. In this work, the effects of the nanowire geometry on their waveguiding properties are studied both experimentally and numerically. Cut-off wavelength dependence on the nanowire diameter is analyzed to demonstrate the pathways for fabrication of low-loss and subwavelength cross-section waveguides for visible and near-infrared (IR) ranges. Probing the waveguides with a supercontinuum laser unveils the filtering properties of the nanowires due to their resonant action. The nanowires exhibit perfect elasticity allowing fabrication of curved waveguides. It is demonstrated that for the nanowire diameters exceeding the cut-off value, the bending does not sufficiently reduce the field confinement promoting applicability of the approach for the development of nanoscale waveguides with a preassigned geometry. Optical X-coupler made of two GaP nanowires allowing for spectral separation of the signal is fabricated. The results of this work open new ways for the utilization of GaP nanowires as elements of advanced photonic logic circuits and nanoscale interferometers.

The existence of conventional magnetic ions may not be necessary for the magnetism of 2D transition metal dichalcogenides (TMDs), but the local magnetic moment can effectively regulate the magnetism. Recent enhancement approaches for introduction of magnetism into 2D TMDs mainly use element doping, vacancy defects, heterostructures, phase modulation, adsorption, and also electron irradiation induction, O plasma treatment, etc.

Abstract

Two-dimensional transition metal dichalcogenides (2D TMDs) present promising applications in various fields such as electronics, optoelectronics, memory devices, batteries, superconductors, and hydrogen evolution reactions due to their regulable energy band structures and unique properties. For emerging spintronics applications, materials with excellent room-temperature ferromagnetism are required. Although most transition metal compounds do not possess room-temperature ferromagnetism on their own, they are widely modified by researchers using the emerging strategies to engineer or modulate their intrinsic properties. This paper reviews recent enhancement approaches to induce magnetism in 2D TMDs, mainly using doping, vacancy defects, composite of heterostructures, phase modulation, and adsorption, and also by electron irradiation induction, O plasma treatment, etc. On this basis, the produced effects of these methods for the introduction of magnetism into 2D TMDs are compressively summarized and constructively discussed. For perspective, research on magnetic doping techniques for 2D TMDs materials should be directed toward more reliable and efficient directions, such as exploring advanced design strategies to combine dilute magnetic semiconductors, antiferromagnetic semiconductors, and superconductors to develop new types of heterojunctions; and advancing experimentation strategies to fabricate the designed materials and enable their functionalities with simultaneously pursuing the upscalable growth methods for high-quality monolayers to multilayers.

Nature Electronics, Published online: 15 May 2023; doi:10.1038/s41928-023-00966-4

An elastomer–semiconductor–elastomer stack structure can allow an intrinsically brittle n-type organic semiconductor to be stretched by 50% and used to make fully stretchable complementary electronics.

A general method is demonstrated for the preparation of high-quality van der Waals heterostructures in solution through an electrochemical strategy. The produced van der Waals heterostructures exhibit strong interlayer coupling, extraordinary structural integrity, large lateral dimension and good optoelectronic properties.

Abstract

Two-dimensional van der Waals heterostructures (2D vdWHs) have recently gained widespread attention because of their abundant and exotic properties, which open up many new possibilities for next-generation nanoelectronics. However, practical applications remain challenging due to the lack of high-throughput techniques for fabricating high-quality vdWHs. Here, we demonstrate a general electrochemical strategy to prepare solution-processable high-quality vdWHs, in which electrostatic forces drive the stacking of electrochemically exfoliated individual assemblies with intact structures and clean interfaces into vdWHs with strong interlayer interactions. Thanks to the excellent combination of strong light absorption, interfacial charge transfer, and decent charge transport properties in individual layers, thin-film photodetectors based on graphene/In₂Se₃ vdWHs exhibit great promise for near-infrared (NIR) photodetection, owing to a high responsivity (267 mA W⁻¹), fast rise (72 ms) and decay (426 ms) times under NIR illumination. This approach enables various hybrid systems, including graphene/In₂Se₃, graphene/MoS₂ and graphene/MoSe₂ vdWHs, providing a broad avenue for exploring emerging electronic, photonic, and exotic quantum phenomena.

This study proposes a surface Li₂CO₃ mediated phosphorization strategy to construct a Li₃PO₄ nanolayer on Ta-substituted LLZO (LLZTO). This study takes advantage of the reaction with Li₂CO₃ and neutralizes the chemical environment of LLZTO surfaces to ensure high air stability and effective suppression of dehydrofluorination to achieve stable interfaces in solid-state batteries and excellent electrochemical performance.

Abstract

Composite polymer electrolytes (CPEs) are subject to interface incompatibilities due to the space charge layer of ceramic and polymer phases. The intensive dehydrofluorination of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) incorporating Li₇La₃Zr₂O₁₂ (LLZO) significantly compromises electro-chemo-mechanical properties and compatibilities with electrodes. Herein, this study addresses the challenges by precisely phosphatizing LLZO surfaces through a surface Li₂CO₃ mediated chemical reaction. The designed neutral chemical environment of LLZO surfaces ensures high air stability and effective suppression of PVDF-HFP dehydrofluorination. This greatly facilitates the uniform distribution of ceramic and polymer phases, and fast interfacial Li⁺ exchange, establishing high-throughput ion percolation pathways and distinctly enhancing ionic conductivity and transference number. Moreover, the dramatically reduced formation of dehydrofluorination products and an in situ formed interphase layer between phosphatized surface and a Li metal anode stabilize the Li/CPE and cathode/CPE interfaces, which provide a symmetric Li/Li cell and solid-state Li/LiFePO₄ and Li/LiNi_0.8Co_0.1Mn_0.1O₂ cells an exceptional cycling performance at room temperature. This study emphasizes the vital importance of achieving electro-chemo-mechanical compatibilities for CPEs and provides a new waste to wealth route.

Recent advances in graphene field-effect transistor (GFET) biosensors are summarized, including device design and operation, biomarker analysis, and prototypical applications. The advantages and limitations of GFETs and the possible technical solutions to existing challenges are discussed, providing suggestions on the future development of GFET biosensors in biomarker analysis and healthcare monitoring applications.

Abstract

Biomarkers are primary indicators for precise diagnosis and treatment. The early identification of health biomarkers has been sustained by the evolutionary success in sensor technologies. Among them, graphene field-effect transistor (GFET) biosensors have exhibited major advantages such as an ultrashort response time, high sensitivity, easy operation, capability of integration, and label-free detection. Owing to the atomic thickness, graphene restricts charge carrier flow merely at the material surface and responds to foreign stimuli directly, leading to effective signal acquisition and transmission. Here, this review summarizes the latest advances in GFET biosensors in a comprehensive manner that contains the device design, working principle, surface functionalization, and proof-of-concept applications. It provides a comprehensive survey of GFET biosensors with regard to biomarker analysis at the single-device level and integrated prototypes that include wearable sensors, biomimetic systems, healthcare electronics, and diagnostic platforms. Moreover, there is discussion on the long-standing research efforts and outlook for the future development of GFET sensor systems from lab to fab.

This work designs a series of fullerene-based 1D chains with excellent ferroelectric and ferromagnetic properties. Due to the cooperative effect between fullerenes and metal linkers, their spontaneous polarization is higher than freestanding U₂C@I _h(7)-C₈₀ by about two to four times. Meanwhile, robust 1D ferromagnetic/antiferromagnetic semiconductors with high Curie or Neel temperature are obtained.

Abstract

One-dimensional (1D) magnetoelectric multiferroics are promising multifunctional materials for miniaturized sensors, actuators, and memories. However, 1D materials with both ferroelectricity and ferromagnetism are quite rare. Herein, using first-principles calculations, a series of fullerene-based 1D chains, namely U₂C@C₈₀-M (M = Cr, Mn, Mo, and Ru) 1D chains with both ferroelectric (FE) and ferromagnetic (FM) properties is designed. Compared to individual U₂C@I _h(7)-C₈₀, the spontaneous polarization (Ps) in 1D chains is enhanced by about two to four times owing to the interaction between U₂C@I _h(7)-C₈₀ fullerene and M (M = Cr, Mn, Mo, and Ru) atoms. Meanwhile, the introduction of transition metal atoms dopes electrons into U's 5f orbitals, leading to numerous intriguing magnetic properties, such as U₂C@C₈₀-Cr and U₂C@C₈₀-Mo as 1D ferromagnetic semiconductors, U₂C@C₈₀-Ru as 1D ferrimagnetic (FiM) semiconductor, and U₂C@C₈₀-Mn as 1D antiferromagnetic (AFM) semiconductor. Excitingly, it is found that magnetic ordering and electrical polarization can be modulated independently by linking different transition metal atoms. These findings not only broaden the range of 1D multiferroic materials, but also provide promising candidates for novel electronic and spintronic applications.

Abstract

As promising components of future integrated circuits (ICs), field-effect transistors (FETs) based on semiconducting nanomaterials are being extensively investigated. As the most essential component of ICs, inverters are favored to be demonstrated at the infant stage of emerging technologies. However, systematic research is absent to reveal how the parameters of transistors affect the performance of inverters, e.g. the voltage transfer characteristics (VTCs). In this work, systematic analysis about the dependency between transistor- and inverter-level metrics have been carried out for both complementary metal-oxide-semiconductor (CMOS) and monotype (p-type-only and n-type-only) technologies, which is further experimentally demonstrated by carbon nanotube FETs and ICs. We also propose guidelines towards the high noise margin and rail-to-rail inverter design based on nanomaterials.

Nature Nanotechnology, Published online: 11 May 2023; doi:10.1038/s41565-023-01403-5

Domain wall formation and propagation using a small electric voltage are demonstrated in ferro-rotational 1T-TaS2, although the ferroic order does not couple with electromagnetic fields, providing an opportunity for the manipulation and application of ferro-rotational order.

Nature Communications, Published online: 11 May 2023; doi:10.1038/s41467-023-38262-6

Emission enhancement and extraction from quantum emitters is a major challenge for photon sources in e.g. quantum photonic networks. Here the authors propose a broadband waveguide platform which allows to boost, extract, and guide quantum emission within integrated photonic networks.

Nature Reviews Materials, Published online: 10 May 2023; doi:10.1038/s41578-023-00560-2

Two-dimensional perovskites with phase-pure structures have considerable potential for optoelectronic applications because of their reduced defects, flattened energy landscape and enhanced lattice protection. This Perspective article investigates advancing progress on achieving phase-pure perovskite by tailoring the precursor interactions and preparation methods and discusses their prominent optoelectronic properties and applications.

Nature, Published online: 10 May 2023; doi:10.1038/d41586-023-01366-6

Most light-field sensors — devices that detect the angles of incoming light rays to reconstruct 3D scenes — can detect light only in the ultraviolet and visible wavelength ranges. A newly developed light-field sensor comprising perovskite nanocrystals encodes the angles of incoming visible-light beams and X-rays as different colours.