Jiuxiang Dai

In this paper, we present AgErP2Se6, a layered two-dimensional material that produces bright ultra-narrow photoluminescence emission bands across a wide wavelength range (350–1,550 nm). The down- and up-converted emission comes from the octahedrally coordinated Er3+ ions in the lattice. The emission bands can be used for ratiometric sensing of temperature and pressure. We also observe a thickness-dependent Purcell enhancement of some emission bands in exfoliated flakes.

This work reports a self-driven Te/Bi₂Se₃ van der Waals heterojunction-based photodetector with a well-defined heterointerface and type-II band alignment, which shows excellent broadband photoresponse ranging from 365 nm to 4.3 µm and a high responsivity of 880 mA W⁻¹ at 1550 nm. It also exhibits uniformly polarization-sensitive photoresponse, as verified by optical communication and polarization imaging applications at 2 µm.

Abstract

Broadband detection technology is crucial in the fields of astronomy and environmental surveying. Two dimensional (2D) materials have emerged as promising candidates for next-generation broadband photodetectors with the characteristics of high integration, multi-dimensional sensing, and low power consumption. Among these, 2D tellurium (Te) is particularly noteworthy due to its excellent mobility, tunable bandgap, and air stability. However, the performance of the Te-based photodetector has been hindered by high dark current and cut-off wavelength limitations associated with its intrinsic bandgap. Here, the Te / bismuth selenide (Bi₂Se₃) van der Waals (vdWs) p-n heterojunction with a clean interface and type-II band alignment, designed to address these challenges are presented. The Te/Bi₂Se₃ heterojunction photodetectors demonstrate an ultra-broadband photodetection range from Ultraviolet (UV) to Mid-infrared (MIR) (365 nm–4.3 µm) and a high responsivity up to 880 mA W⁻¹ at 1550 nm under zero bias. Moreover, benefiting from the anisotropy crystal structure of Te, the photodetector shows an obvious polarization-sensitive photoresponse and enormous potential in optical communication and polarization imaging. This work hereby provides significant insight into low-powered, high-performance, and broadband vdWs heterojunction photodetectors and their functional applications.

This review offers a comprehensive overview of the advancements in 2D materials synthesis by salt-assisted methods, including molten salt method (MSM), salt-assisted chemical vapor deposition (SA-CVD), and salt-template method (STM). It highlights the advantages, underlying mechanisms, and recent innovations of these methods. Challenges and future directions are also discussed, emphasizing salt-assisted strategies to produce high-quality 2D materials.

Abstract

Two-dimensional (2D) materials have been attracting extensive interest due to their remarkable chemical, optical, electrical, and magnetic properties, making them ideal candidates for a broad range of applications. Developing facile synthesis methods that can fabricate high-quality 2D materials in an efficient, scalable, and cost-effective way is essential. Among the emerging techniques, salt-assisted methods to synthesize 2D materials, including molten salt method, salt-assisted chemical vapor deposition, and salt-template method, has demonstrated significant potential in fulfilling these requirements. This review highlights recent advancements in the synthesis of 2D materials through salt-assisted methods, focusing on their preparation processes and wide-ranging applications. It also explores the role of salts, in various forms, in directing the formation of 2D structures, providing insights for strategic synthesis design. Finally, challenges and future directions in salt-assisted synthesis are discussed, emphasizing strategies to enable controllable, high-yield production of 2D materials.

The effects of dimensional reduction on magneto-transport behavior are systematically investigated in VS₂ nanosheets. Nontrivial magnetoresistance behavior with twice sign reversals is observed in 2D nanosheets, as a consequence of delicate interplay among spin, orbital and structural degrees of freedom under a strong electron correlation background. These appealing physical properties make it a promising platform for exploring exotic electronic phenomena.

Abstract

The concepts of quantum interference and charge localization have profoundly influenced the understanding of electronic conductivity in materials. While magnetoresistance behavior with monotonic or singly transitional dependence on applied magnetic fields is widely observed in different materials, it remains scarce to find one that features multiple transitions in magnetoresistance. Here, the effects of dimensional crossover on electronic and magneto-transport behavior in vanadium disulfide (VS₂) are reported. Dual transitions in magnetoresistance are observed in 5 nm VS₂ nanosheets, resulting from the competition of multiple mechanisms relevant to charge transport as the external magnetic field changes. The nontrivial magneto-transport phenomenon revealed in the system is attributed to the effect of strong electron correlation and the delicate interplay among spin, orbital, and structural degrees of freedom. These appealing physical properties make 2D VS₂ a promising platform for exploring exotic electronic phenomena.

2D Cs₂Bi₃X₉ (X = Br, Cl, I) perovskite crystals with variable lattice constants and engineered bandgaps are synthesized via adaptive heteroepitaxy on c-sapphire substrates. Photodetectors based on these epitaxial crystals exhibit significantly improved photodetection performance, indicating the effectiveness of epitaxial growth strategy for high-quality crystals. This work advances the integration of multicomponent 2D materials on dielectric substrates for optoelectronic applications.

Abstract

The heteroepitaxy of 2D materials with engineered bandgaps are crucial to broaden the spectral response for their integrated optoelectronic devices. However, it is a challenge to achieve the high-oriented epitaxy and integration of multicomponent 2D materials with varying lattice constants on the same substrate due to the limitation of lattice matching. Here, in-plane adaptive heteroepitaxy of a series of high-oriented 2D cesium bismuth halide (Cs₃Bi₂X_9, X = I, Br, Cl) single crystals with varying lattice constants from 8.41 to 7.71 Å is achieved on c-plane sapphire with distinct lattice constant of 4.76 Å at a low temperature of 160 °C in an air ambient, benefiting from tolerable interfacial strain by switching compressive stress to tensile stress during a 30° rotation of crystal orientation. First-principles calculation demonstrates that those are all thermodynamically stable phases, deriving from multiple minima of interfacial energy between single crystals and sapphire substrate. The detectivity of Cs₃Bi₂I₉ photodetector reaches up to 3.7 × 10¹² Jones, deriving from high single-crystal quality. This work provides a promising experimental strategy and basic theory to boost the heteroepitaxy and integration of 2D single crystals with varying lattice constants on low-cost dielectric substrate, paving the way for their applications in integrated optoelectronics.

This research presents a significant advancement in nanophotonics by utilizing ionic liquid (IL) as a dielectric layer to modulate carrier concentrations in indium phosphide (InP) nanolasers. The study demonstrates efficient, room-temperature switching between photoluminescence and lasing with a 22-fold extinction ratio, offering promising applications for integrated photonic circuits.

Abstract

Nanoscale light sources are demanded vigorously due to rapid development in photonic integrated circuits (PICs). III-V semiconductor nanowire (NW) lasers have manifested themselves as indispensable components in this field, associated with their extremely compact footprint and ultra-high optical gain within the 1D cavity. In this study, the carrier concentrations of indium phosphide (InP) NWs are actively controlled to modify their emissive properties at room temperature. The InP NW lasers can achieve repetitive switching between photoluminescence (PL) and lasing with an extinction ratio of 22-fold by applying a gate voltage of 3 V using ionic liquid (IL) as a dielectric layer. IL brings forth ultra-high capacitance due to the nanometer-wide electric double layer (EDL) between interfaces, mapping out gating efficiency of ≈100-fold compared to the conventional bottom gate configurations. This IL-embedded nanolaser device can be a promising platform for the advanced integrated nanophotonic system.

A novel experimental platform is presented, capable of performing electrochemical lithiation of van der Waals materials and allowing for simultaneous multimodal characterization of the material using both ultrafast electron diffraction and nonlinear optical methods. By monitoring the behavior of the interlayer shear phonon in WTe₂, light lithiation is found to stabilize the otherwise dynamically fluctuating and anharmonic structure at room-temperature.

Abstract

The unique layer-stacking in two-dimensional (2D) van der Waals materials facilitates the formation of nearly degenerate phases of matter and opens novel routes for the design of low-power, reconfigurable functional materials. Electrochemical ion intercalation between stacked layers offers a promising approach to stabilize bulk metastable phases and to explore the effects of extreme carrier doping and strain. However, in situ characterization methods to study the structural evolution and dynamical functional properties of these intercalated materials remains limited. Here a novel experimental platform is presented capable of simultaneously performing electrochemical lithium-ion intercalation and multimodal ultrafast characterization of the lattice using both electron diffraction and nonlinear optical techniques. Using the layered semimetal WTe₂ as a model system, the interlayer shear phonon mode that modulates stacking between 2Dlayers is probed, showing that small amounts of lithiation enhance the amplitude and lifetime of the phonon, contrary to expectations. This results from the dynamically fluctuating and anharmonic structure between nearly degenerate phases at room temperature, which can be stabilized by electronic carriers accompanying the inserted lithium ions. At high lithiation, the T_d’ structure emerges and quenches the phonon response. This work defines new approaches for using electrochemistry to engineer the dynamic structure of 2D materials.

This work provides optical evidence for interfacial strain-induced ferroelectric tuning and enhancement in CuInP₂S₆ via ferroelectric substrate through photoluminescence spectroscopy, combined with piezoresponse force microscopy and density functional theory calculation, which demonstrates enhanced and unit-aligned polar alignment, interface strain-induced lattice change, and enhanced T _c in CuInP₂S₆ on ferroelectric substrate, paving the path for its implementation in novel nanophotonics and optoelectronics.

Abstract

The precise domain control in ferroelectric CuInP₂S₆ (CIPS) remains challenging. A promising approach is by interfacing CIPS with the ferroelectric layer, but interface-driven ferroelectricity tunning mechanism remains unclear. Here, the demonstration of interfacial strain-induced ferroelectric tuning and enhancement in CIPS via ferroelectric substrate is reported by photoluminescence (PL) spectroscopy, combined with piezoresponse force microscopy (PFM) and density functional theory (DFT) calculations. PFM studies show that thin CIPS flakes form the same domain as that of ferroelectric PbZr_0.52Ti_0.48O₃ (PZT) and P(VDF-TrFE) films, suggesting enhanced polar alignment in CIPS via ferroelectric substrate. PL analyses show that a significant redshift occurs for PL emission of CIPS on ferroelectric substrate compared with that on conventional substrate, revealing interface tensile strain-induced lattice change in CIPS, as further confirmed by DFT calculation. By analyzing PL spectra of monolayer MoS₂ on CIPS/PZT, the polarization of CIPS is evidenced to be anti-aligned with that of ferroelectric substrate. In situ, temperature-dependent PL studies show that thin CIPS on ferroelectric substrate exhibits enhanced Curie temperature of higher than 200 °C. This study not only provides an effective material strategy to engineer the ferroelectric properties of CIPS but also offers a simple optical method to reveal interface-driven ferroelectricity modulation mechanism in CIPS.

A highly modulated interlayer spacing is observed for the first time in the epitaxial 2D spirals with electron correlations. Scalable synthesis of the epitaxial TaS₂ spirals is achieved with customized CVD reactions. An intertwined CDW-Mott state appears at room-temperature in the epitaxial 1T-TaS₂ spirals, offering a platform to study collective properties at high temperatures.

Abstract

Tantalum disulfide (1T-TaS₂), being a Mott insulator with strong electron correlation, is highlighted for diverse collective quantum states in the 2D lattice, including charge density wave (CDW), spin liquid, and unconventional superconductivity. The Mott physics embedded in the 2D triangular CDW lattice has raised debates on stacking-dependent properties because interlayer interactions are sensitive to van der Waals (vdW) spacing. However, control of interlayer distance remains a challenge. Here, spiral lattices in the epitaxial TaS₂ spirals are studied to probe collective properties with tunable interlayer interactions. A scalable synthesis of epitaxial TaS₂ spirals is presented. A more than 50%-increased interlayer spacing enables prototype decoupled monolayers for enhanced electronic correlation exhibiting Mott physics at room-temperature and a simplified system to explore collective properties in vdW materials.

An efficient and straightforward transfer process is developed for 4-inch wafer-scale Ti₃C₂T_x MXene films, in which damage and deformation are minimized. Uniform vdW stacking of several types of large-area heterojunctions MXene/MoS₂/MXene are well demonstrated. By utilizing 2D liquid reductants to modify the MXene/MoS₂ interface, a more than 100-fold increase in carrier transfer efficiency is achieved.

Abstract

Wafer-scale transfer processes of 2D materials significantly expand their application space in scalable microelectronic devices with excellent and tunable properties through van der Waals (vdW) stacking. Unlike many 2D materials, wafer-scale transfer of MXene films for vdW contact engineering has not yet been reported. With their rich surface chemistry and tunable properties, the transfer of MXenes can enable enormous possibilities in electronic devices using interface engineering. Taking advantage of the MXene hydrophilic surface, a straightforward, green, and fast process for the transfer of MXene films at the wafer scale (4-inch) is developed. Uniform vdW stacking of several types of large-area heterojunctions including MXene/MXene (Ti₃C₂T _x , Nb₂CT _x, and V₂CT _x ), MXene/MoS₂, and MXene/Au is further demonstrated. Multilayer support is applied to minimize damage or deformation in the transfer process of patterned Ti₃C₂T _x film. It allows us to fabricate thin film transistors and manipulate the MXene/MoS₂ interface through the intercalation of various 2D liquids. Particularly noteworthy is the significant enhancement of the interfacial carrier transfer efficiency by ≈2 orders of magnitude using hydrogen iodide (HI) intercalation. This finding indicates a wide range of possibilities for interface engineering by transferring MXene films and employing liquid-assisted interfacial intercalation.

A versatile vacuum-enabled synthesis method is developed to produce metal nanocrystals with controlled morphologies using 2D materials such as graphene oxide and Ti₃C₂T _x MXene. By managing metal loading and selecting specific 2D materials and drying techniques, the dimensions and distribution of the metal nanocrystals on 2D materials can be tuned. Freeze-dried Pt–MXene heterostructures demonstrate exceptional catalytic activity in the hydrogenation of phenylacetylene.

Abstract

The synthesis of low-dimensional metal nanocrystals with precise atom-to-nanoscale structure control is crucial for modulating their physicochemical properties. Traditional synthetic routes encounter challenges due to isotropic metallic bonding, which leads to limited control over metal nanostructures. Herein, a versatile approach is developed using various 2D material (2DM) nanoconfinements to produce a wide range of metal nanocrystals with controllable morphologies. Utilizing graphene oxide (GO) and Ti₃C₂T _x  MXene nanosheets, thin multilayer films are assembled through vacuum filtration and are crosslinked with tetraammineplatinum(II) nitrate (TPtN), followed by in situ thermal reduction. By controlling the concentration of TPtN solution, precise loadings of platinum (Pt) are attained while preserving the nanoconfinement integrity. Two water removal techniques, air-drying and freeze-drying, are investigated to assess their impacts on resultant morphologies of Pt nanocrystals. Transmission electron microscopy and molecular dynamics simulations demonstrate high-aspect-ratio Pt nanosheets on MXene substrates and few-atom Pt nanoclusters on GO substrates. A decrease in size distribution is observed upon the use of freeze-drying. In the semihydrogenation reaction of phenylacetylene, freeze-dried Pt–MXene heterostructures achieve a high turnover frequency of 2.93 s⁻¹. This comprehensive study highlights the potential of utilizing 2DM nanoconfinement to synthesize metal nanostructures for catalysts and beyond.

The design and implementation of locally introducing Sm₂O₃ damping structures in epitaxial SmCoO₃ films help release overload stress and address stress disappearance in films beyond the critical size. For the first time, epitaxially grown SmCoO₃ thin films are reported, exhibiting ferromagnetism and the highest observed ferroelectricity at room temperature.

Abstract

Strain is an effective means of tuning the crystal structure to obtain a variety of fascinating properties, but how to apply flexible strain to meet the different needs of the film at each location has rarely been reported. In this study, a novel approach for designing strain-damping structures that facilitate the imposition of flexible strain is introduced. A wide range of strain modulation is demonstrated in SmCoO₃ films (a-axis:+4.5%–+1.7%, b-axis: +3.2%–+0.4%, c-axis:+2.2%–+1.4%) under positive pressure by introducing Sm₂O₃ as a dopant. When SmCoO₃ films are subjected to triaxial tensile strain, they exhibit a ferroelectric polarization of 7.12 µC cm⁻². Through positive pressure modulation, resulting in a further increase in the ferroelectric polarization (up to 11.62 µC cm⁻², which represents the maximum performance of the orthogonal rare earth transition metal oxide family). Moreover, the electron spin order can be effectively controlled, and the film's saturation magnetization increases to 14.83 emu cm⁻³ (+94.1%). This damping structure allows for flexible modulation of chemical strain in epitaxial film, achieving a delicate balance between film strain and structure, which provides valuable insights for all ferroelectrics based on structural distortion.

Nature, Published online: 18 December 2024; doi:10.1038/d41586-024-04109-3

A battery-like technology uses a metal called tantalum to create an equivalent of digital 0s and 1s.

Nature, Published online: 18 December 2024; doi:10.1038/s41586-024-08236-9

Single-crystalline materials can be grown on amorphous surfaces at below 400 °C, enabling monolithic three-dimensional integration of vertically stacked transistors.

Nature Electronics, Published online: 19 December 2024; doi:10.1038/s41928-024-01329-3

Developments in the fabrication processes of monolithic complementary field-effect transistors allow inverters with a 48 nm gate pitch to be created.

npj 2D Materials and Applications, Published online: 19 December 2024; doi:10.1038/s41699-024-00519-z

Memristors based on two-dimensional h-BN materials: synthesis, mechanism, optimization and application

Nature, Published online: 19 December 2024; doi:10.1038/s41586-024-08525-3

Signatures of ambient pressure superconductivity in thin film La₃Ni₂O₇

An intelligent generic high-throughput oscillatory shear technology (iGHOST) for fabricating diverse, size-controllable monodispersed microrobots is proposed. Especially, the iGHOST-prepared magnetically responsive lipiodol calcium alginate (MagLiCA) microrobots enable X-ray real-time imaging navigated endovascular embolization. Using a permanent magnet for navigation, selective embolization is successfully performed in vivo in rabbit ear, kidney, and liver models.

Abstract

Microrobots for endovascular embolization face challenges in precise delivery within dynamic blood vessels. Here, an intelligent generic high-throughput oscillatory shear technology (iGHOST) is proposed to fabricate diversely programmable, multifunctional microrobots capable of real-time visual guidance for in vivo endovascular embolization. Leveraging machine learning (ML), key synthesis parameters affecting the success and sphericity of the microrobots are identified. Therefore, the ML-optimized iGHOST enables continuous production of uniform microrobots with programmable sizes (400−1000 µm) at an ultrahigh rate exceeding 240 mL h⁻¹ by oscillatory segmenting fluid into droplets before ionic cross-linking, and without requiring purification. Particularly, the iGHOST-fabricated magnetically responsive lipiodol-calcium alginate (MagLiCA) microrobots are highly distinguishable under X-ray imaging, which allows for precise navigation in fluid flows of up to 4 mL min⁻¹ and accurate embolization in liver and kidney blood vessels, thus addressing the current issues. Crucially, MagLiCA microrobots possess drug-loading capabilities, enabling simultaneous embolization and site-specific treatment. The iGHOST process is an intelligent, rapid, and green manufacturing method, which can produce size-controllable, multifunctional microrobots with the potential for precise drug delivery and treatment under real-time imaging across various medical applications.

The integration of 2D transition metal dichalcogenides (TMDs) with other materials presents a promising approach to overcome inherent limitations and enable the development of novel functionalities. Herein, the integration of 0D NMs with 2D TMDs to develop high-performance photodetectors is reviewed. The review provides a comprehensive overview of different types of 0D NMs, including plasmonic nanoparticles (NPs), up-conversion NPs, quantum dots (QDs), nanocrystals (NCs), and small molecules.

Abstract

The integration of 2D transition metal dichalcogenides (TMDs) with other materials presents a promising approach to overcome inherent limitations and enable the development of novel functionalities. In particular, 0D nanomaterials (0D NMs) offer notable advantages for photodetection, including broadband light absorption, size-dependent optoelectronic properties, high quantum efficiency, and good compatibility. Herein, the integration of 0D NMs with 2D TMDs to develop high-performance photodetectors is reviewed. The review provides a comprehensive overview of different types of 0D NMs, including plasma nanoparticles (NPs), up-conversion NPs, quantum dots (QDs), nanocrystals (NCs), and small molecules. The discussion starts with an analysis of the mechanism of 0D NMs on 2D TMDs in photodetection, exploring various strategies for improving the performance of hybrid 2D TMDs/0D NMs. Recent advancements in photodetectors combining 2D TMDs with 0D NMs are investigated, particularly emphasizing critical factors such as photosensitivity, photogain, specific detectivity, and photoresponse speed. The review concludes with a summary of the current status, highlighting the existing challenges and prospective developments in the advancement of 0D NMs/2D TMDs-based photodetectors.

Nature Electronics, Published online: 16 December 2024; doi:10.1038/s41928-024-01272-3

Comprehensive device simulations reveal the potential of ultra-scaled field-effect transistors based on two-dimensional channel materials.

Nature Electronics, Published online: 16 December 2024; doi:10.1038/s41928-024-01289-8

A simulation framework for three-dimensionally structured transistors based on two-dimensional materials shows that they could be used to continue complementary metal–oxide–semiconductor scaling with performance and energy enhancements.