Jiuxiang Dai

Nature Communications, Published online: 22 May 2024; doi:10.1038/s41467-024-48690-7

2D AMX2 compounds (where A is a monovalent metal ion, M is a trivalent metal, and X is a chalcogen) are a family of materials with coupled ionic-electronic properties. Here, the authors report a chemical vapor deposition strategy to fabricate 20 types of 2D AMX2 flakes, exhibiting superionic conductivity or room temperature ferroelectricity.

Nature, Published online: 22 May 2024; doi:10.1038/s41586-024-07406-z

We develop a low-temperature, damage-free process using van der Waals lamination to integrate multiple circuit tiers into a monolithic three-dimensional device, incorporating unique multi-tier functionality and resolving legacy issues with the layering technology.

Highlights

• Recent progress on the applications of 2D materials in perovskite solar cells is discussed from the views of bottom interfaces, top interfaces, and electrodes.

• The roles of van der Waals heterojunction in enhancing the performance of perovskite solar cells are highlighted.

• The future directions and challenges in development of 2D materials-based perovskite solar cells are provided.

Membrane separation processes are essential in gas separation applications, requiring continuous development to tackle modern challenges. Novel 2D nanomaterials proved to enable excellent molecular transport properties. This study introduces gas separation performances of vanadium pentoxide nanoribbons based membranes. V₂O₅ membranes surpassed Robeson's upper bounds for He/N₂ (2008) and He/CO₂ (2019), showcasing the potential of V₂O₅ 2D materials in gas separation.

Abstract

Membrane separation processes play a crucial role in gas separation applications, with the need for ongoing development to fulfill new needs for today's challenges. For this purpose, novel 2D nanomaterials are progressively showing promise over conventional polymer-based membrane material, exhibiting excellent molecular transport properties. Beyond the 2D materials already studied in this field, this article presents the first gas separation performances of vanadium pentoxide membrane. Brand new in gas separation topic, 2D van der Waals nanoribbons of V₂O₅ are successfully synthesized and layered on an anodic aluminum oxide substrate. Gas permeation analysis of He, N₂, and CO₂ are performed on various membranes made from different quantities of the nanomaterial. Gas permeance results suggest a deviation from an expected Knudsen diffusion mechanism of the V₂O₅-based membrane for He separation. The ideal selectivities of He/N₂ and He/CO₂ are compared to Robeson's upper bound for polymeric membranes. V₂O₅ membranes, prepared with the highest V₂O₅ quantity, exceeded the upper bound from 2008 for He/N₂ and 2019 (the most recent) for He/CO₂, demonstrating the interesting potential of V₂O₅ 2D materials for gas separation.

Nature Electronics, Published online: 24 May 2024; doi:10.1038/s41928-024-01183-3

A complementary oxide semiconductor

Nature Electronics, Published online: 24 May 2024; doi:10.1038/s41928-024-01184-2

Wafer-scale probing of spin qubits

Nature Communications, Published online: 24 May 2024; doi:10.1038/s41467-024-48634-1

The authors study tunneling junctions in rhombohedral MoS2 bilayers and correlate their performance with the local domain layout. They show that the switching behavior in sliding ferroelectrics is strongly dependent on the pre-existing domain structure.

Nature Communications, Published online: 25 May 2024; doi:10.1038/s41467-024-48799-9

There are now several van der Waals magnets that have been shown to host skyrmions, however, these are typically hampered by a low Curie temperature, restricting the temperature at which the skyrmions can exist. Here, Zhang, Jiang, Jiang and coauthors find a skyrmion lattice in the van der Waals magnet Fe3 − xGaTe2 above room temperature and demonstrate the critical role of symmetry breaking in crystal lattice in the origin of these skyrmions.

This review summarizes significant advancements and innovations in the developments in applying scanning probe microscopy (SPM) techniques to explore 2D materials. It highlights the capability of SPM to achieve the in situ measurements under various chemical conditions. Moreover, it outlines the challenges and potential opportunities for future exploration and application in the evolving area of SPM techniques.

Abstract

2D materials are intriguing due to their remarkably thin and flat structure. This unique configuration allows the majority of their constituent atoms to be accessible on the surface, facilitating easier electron tunneling while generating weak surface forces. To decipher the subtle signals inherent in these materials, the application of techniques that offer atomic resolution (horizontal) and sub-Angstrom (z-height vertical) sensitivity is crucial. Scanning probe microscopy (SPM) emerges as the quintessential tool in this regard, owing to its atomic-level spatial precision, ability to detect unitary charges, responsiveness to pico-newton-scale forces, and capability to discern pico-ampere currents. Furthermore, the versatility of SPM to operate under varying environmental conditions, such as different temperatures and in the presence of various gases or liquids, opens up the possibility of studying the stability and reactivity of 2D materials in situ. The characteristic flatness, surface accessibility, ultra-thinness, and weak signal strengths of 2D materials align perfectly with the capabilities of SPM technologies, enabling researchers to uncover the nuanced behaviors and properties of these advanced materials at the nanoscale and even the atomic scale.

Theoretical studies indicate the designing of functionalized MoS₂ as electrocatalysts for energy conversion. The doping method tailors the electrochemical activity for the hydrogen evolution reaction visualized by scanning electrochemical cell microscopy. Moreover, localized measurement of the potential of zero charges and Kelvin probe microscopy support the findings on the impact of different transition metal-functionalization on work function and electrochemical activity of MoS₂.

Abstract

Finding strategies to enhance catalysts’ electrochemical activity is based on controlling the material design. Bidimensional materials (2DM) such as MoS₂ are explored as catalysts for the hydrogen evolution reaction (HER). A comprehensive study of the effects of doping 2D materials with transition metals based on theoretical predictions in tandem with experimental investigation correlates the doping type to the changes in the electronic and electrochemical activity. Localized electrochemical maps obtained by scanning electrochemical cell microscopy (SECCM) reveal that Ti-doping induces a heterogeneous increase in 2H-MoS₂ basal plane electrochemical activity, while Ni-doping induces a homogeneous decrease. Additionally, Kelvin probe microscopy provides insight into Ti-doping, showcasing a decline in the 2H-MoS₂ work function, therefore confirming the predictions from density functional theory simulations. In essence, the findings underscore the potential of transition metal coordination on the 2H-MoS₂ surface as an attractive method for locally doping 2D materials with minimal damage to the crystalline lattice, consequently enhancing the electrochemical activity on the material's basal plane.

Ultrathin non-van der Waals Cr₂S₃ nanosheets (NSs) are prepared through liquid phase exfoliation and utilized in a photoelectrochemical-typephotodetector (PD). The Cr₂S₃ NS-based PD shows self-powered photodetection capability, fast response time, and good long-term stability. A photocurrent density of 39.5 nA cm⁻², photoresponsivity of 622 nA W⁻¹, and detectivity of 0.5 × 10⁷ Jones can be achieved at 350 nm without bias voltage.

Abstract

In the search for new advanced 2D materials for technological applications and to expand the research of non-van der Waals (non-vdW) 2D electronic devices, this study presents a novel strategy for liquid phase exfoliation (LPE) of non-vdW Cr₂S₃ to produce Cr₂S₃ nanosheets (NSs). By utilizing N-methyl-2-pyrrolidone (NMP), bulk Cr₂S₃ is separated along the (001) plane, resulting in the formation of NSs with an average thickness of ≈3 nm. Various characterization techniques are applied to the Cr₂S₃ material before and after LPE. Subsequently, the obtained Cr₂S₃ NSs are integrated into a photoelectrochemical (PEC)-type photodetector (PD) to evaluate the photoelectric conversion efficiency under varying conditions. The findings indicate that the developed PD exhibits a distinct self-powered photodetection capability with a photocurrent (P_ph ) of 39.5 nA cm⁻², a photoresponsivity (R_ph ) of 622 nA W⁻¹, and a detectivity (D*) of 0.5 × 10⁷ Jones under 350 nm irradiation at 0 V. Moreover, the PD demonstrates rapid response time (0.06 s) and good long-term stability (over 15 days), thus providing valuable insight for the advancement of non-vdW Cr₂S₃-based optoelectronic devices.

A novel micropatterning technique that harnesses controlled fracture of 2D Ruddlesden–Popper perovskites are developed, enabling precise control over size and shape variations. Pixelated light-emitting diodes (LEDs) are fabricated by using this method, showcasing minimal degradation even as pixel sizes decrease. Additionally, patterning strategies that can be easily adapted for constructing heterostructures and future optoelectronic devices are presented.

Abstract

Quasi-2D Ruddlesden–Popper perovskite (RPP) have surfaced as a promising candidate for light emitting diodes (LEDs) due to its outstanding optoelectronic properties. However, a reliable approach for patterning RPPs remains elusive due to the use of polar solvents in lithographic processes, which can damage the RPP. Here, a reliable and damage-free dry micropatterning method of RPPs is reported, which also offers a cost/time advantage compared to conventional patterning methods. The sharp edges of high aspect ratio silicon micropillars are used to cut RPPs to a pre-defined shape and then the cut RPPs are delaminated to obtain a patterned array of RPPs. The resultant patterned array exhibits no sign of degradation or discernable difference between adjacent pixels, achieving a ≈100% yield. The obtained array is utilized to fabricate a pixelated LED where a sharp electroluminescence (EL) spectrum peaking at 410 nm with full-width-at-half-maximum (FWHM) of 10 nm is observed. The pixelated devices demonstrate the potential to suppress EQE drops as the pixel size decreases, attributed to both the damage-free micropatterning process and the defect tolerance of RPPs. Moreover, further improvements of the patterning method are demonstrated to avoid parasitic emission and suggest a promising strategy to fabricate pixel-accessible micro-LEDs.

Nature Reviews Materials, Published online: 21 May 2024; doi:10.1038/s41578-024-00692-z

An article in Science presents the design of a hydrogel with n-type semiconducting properties.

Exploring the mechanical degree of freedom, we demonstrates pressure sensors based on 2D non-layered material β-In₂S₃. These devices exhibit remarkable features including broad range, high linearity, and fast response, facilitating efficient sensing over a wide pressure range. Furthermore, we establish the frequency scaling law for β-In₂S₃ nanomechanical resonators, which can enable future wafer-scale design and production of integrated sensors.

Abstract

Two-dimensional (2D) non-layered materials, along with their unique surface properties, offer intriguing prospects for sensing applications. Introducing mechanical degrees of freedom is expected to enrich the sensing performances of 2D non-layered devices, such as high frequency, high tunability, and large dynamic range, which could lead to new types of high performance nanosensors. Here, we demonstrate 2D non-layered nanomechanical resonant sensors based on β-In₂S₃, where the devices exhibit robust nanomechanical vibrations up to the very high frequency (VHF) band. We show that such device can operate as pressure sensor with broad range (from 10⁻³ Torr to atmospheric pressure), high linearity (with a nonlinearity factor as low as 0.0071), and fast response (with an intrinsic response time less than 1 μs). We further unveil the frequency scaling law in these β-In₂S₃ nanomechanical sensors and successfully extract both the Young's modulus and pretension for the crystal. Our work paves the way towards future wafer-scale design and integrated sensors based on 2D non-layered materials.

The article first presents an overview of liquid metal (LM)-printed semiconductor. The material category of LM semiconductor e-inks and their synthesis approaches are summarized comprehensively. The core strategies toward printing semiconductors are systematically outlined. Typical electronic devices as well as their potential applications are illustrated. The article is expected to serve well for many coming endeavors in the area.

Liquid metal (LM) electronic ink (e-ink) is a promising new-generation material for printed electronics. Extended from this ideal platform, such ink can be post-processed or loaded with semiconductor nanoparticles to further make semiconductors in the forms of dots, wires, and films on its surface. In this way, targeted semiconductors can be quickly fabricated and patterned as desired with low cost at around room temperature. This leads to the unconventional bottom-up strategy for direct manufacture of functional devices. Along this direction, a series of p–n junction diodes, field-effect transistors, and light-emitting devices have been developed. LM-printed semiconductor would significantly innovate the classical processes of preparing integrated circuits and electronic devices. To push forward further progress of this cutting-edge frontier, this article is dedicated to present an overview of LM-printed semiconductor. The material category of LM semiconductor e-inks and their synthesis approaches is introduced. Then the core strategies toward printing semiconductors are systematically outlined. Following that, the typical printed semiconductor materials and electronic devices thus constructed as well as their potential applications are summarized. Finally, scientific and technical challenges thus raised are interpreted. Perspective in the area is given.

Protein-based 3D photonic superstructures capable of multi-directional structural color imaging are developed. Embedding programmable designed light diffusion layers into a reconfigurable 3D photonic crystal enables multi-image integration using specular and anisotropic diffuse reflections as different storage channels. The ability to program the platform's assembly configuration allows for multimode image switching, offering opportunities for developing information transformation, storage, and encryption devices.

Abstract

Creating photonic crystals that can integrate and switch between multiple structural color images will greatly advance their utility in dynamic information transformation, high-capacity storage, and advanced encryption, but has proven to be highly challenging. Here, it is reported that by programmably integrating newly developed 1D quasi-periodic folding structures into a 3D photonic crystal, the generated photonic superstructure exhibits distinctive optical effects that combine independently manipulatable specular and anisotropic diffuse reflections within a versatile protein-based platform, thus creating different optical channels for structural color imaging. The polymorphic transition of the protein format allows for the facile modulation of both folding patterns and photonic lattices and, therefore, the superstructure's spectral response within each channel. The capacity to manipulate the structural assembly of the superstructure enables the programmable encoding of multiple independent patterns into a single system, which can be decoded by the simple adjustment of lighting directions. The multifunctional utility of the photonic platform is demonstrated in information processing, showcasing its ability to achieve multimode transformation of information codes, multi-code high-capacity storage, and high-level numerical information encryption. The present strategy opens new pathways for achieving multichannel transformable imaging, thereby facilitating the development of emerging information conversion, storage, and encryption media using photonic crystals.

Machine-learning methods and computational chemistry are combined to develop a comprehensive understanding of coordination defects in amorphous silicon. Fivefold-connected atoms fall into three categories based on their chemical structure, and are found to cluster together, which can be explained based on energetic arguments.

Abstract

The structure of amorphous silicon (a-Si) is widely thought of as a fourfold-connected random network, and yet it is defective atoms, with fewer or more than four bonds, that make it particularly interesting. Despite many attempts to explain such “dangling-bond” and “floating-bond” defects, respectively, a unified understanding is still missing. Here, we use advanced computational chemistry methods to reveal the complex structural and energetic landscape of defects in a-Si. We study an ultra-large-scale, quantum-accurate structural model containing a million atoms, and thousands of individual defects, allowing reliable defect-related statistics to be obtained. We combine structural descriptors and machine-learned atomic energies to develop a classification of the different types of defects in a-Si. The results suggest a revision of the established floating-bond model by showing that fivefold-bonded atoms in a-Si exhibit a wide range of local environments–analogous to fivefold centers in coordination chemistry. Furthermore, it is shown that fivefold (but not threefold) coordination defects tend to cluster together. Our study provides new insights into one of the most widely studied amorphous solids, and has general implications for understanding defects in disordered materials beyond silicon alone.

In this work, InSb nanosheets with tunable thickness are successfully synthesized on arbitrary substrates with growth temperatures as low as 240 °C. These InSb nanosheets exhibit electrical and optoelectronic properties, characterized by significantly high field effect transistor on-off ratios, hole mobility, and negligible leakage currents, offering a promising avenue for advancing III–V complementary metal oxide semiconductor technology.

Abstract

III–V semiconductors possess high mobility, high frequency response, and detection sensitivity, making them potentially attractive for beyond-silicon electronics applications. However, the traditional heteroepitaxy of III–V semiconductors is impeded by a significant lattice mismatch and the necessity for extreme vacuum and high temperature conditions, thereby impeding their in situ compatibility with flexible substrates and silicon-based circuits. In this study, a novel approach is presented for fabricating ultrathin InSb single-crystal nanosheets on arbitrary substrates with a thickness as thin as 2.4 nm using low-thermal-budget van der Waals (vdW) epitaxy through chemical vapor deposition (CVD). In particular, in situ growth has been successfully achieved on both silicon-based substrates and flexible polyimide (PI) substrates. Notably, the growth temperature required for InSb nanosheets (240 °C) is significantly lower than that employed in back-end-of-line processes (400 °C). The field effect transistor devices based on fabricated ultrathin InSb nanosheets exhibit ultra-high on-off ratio exceeding 10⁸ and demonstrate minimal gate leakage currents. Furthermore, these ultrathin InSb nanosheets display p-type characteristics with hole mobilities reaching up to 203 cm² V⁻¹ s⁻¹ at room temperatures. This study paves the way for achieving heterogeneous integration of III–V semiconductors and facilitating their application in flexible electronics.

Dual active centers (Fe/B) motivate the directional conversion of PMS into valuable ¹O₂ solely dependent on the inherent structural properties of catalyst, bypassing the need of conventional electron transfer between the two, which effectively alleviates the unevitable redox cycling limitations of catalyst.

Abstract

A broad range of chemical transformations driven by catalytic processes necessitates the electron transfer between catalyst and substrate. The redox cycle limitation arising from the inequivalent electron donation and acceptance of the involved catalysts, however, generally leads to their deactivation, causing substantial economic losses and environmental risks. Here, a “non-redox catalysis” strategy is provided, wherein the catalytic units are constructed by atomic Fe and B as dual active sites to create tensile force and electric field, which allows directional self-decomposition of peroxymonosulfate (PMS) molecules through internal electron transfer to form singlet oxygen, bypassing the need of electron transfer between catalyst and PMS. The proposed catalytic approach with non-redox cycling of catalyst contributes to excellent stability of the active centers while the generated reactive oxygen species find high efficiency in long-term catalytic pollutant degradation and selective organic oxidation synthesis in aqueous phase. This work offers a new avenue for directional substrate conversion, which holds promise to advance the design of alternative catalytic pathways for sustainable energy conversion and valuable chemical production.

Nature Communications, Published online: 18 May 2024; doi:10.1038/s41467-024-48636-z

The authors observe multiferroicity in a single-layer non van der Waals material, CuCrSe2. The coexistence of room-temperature ferroelectricity and ferromagnetism up to 120 K is corroborated by a set of comprehensive experimental techniques.