Jiuxiang Dai

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.

Nature Communications, Published online: 16 May 2024; doi:10.1038/s41467-024-48522-8

Rhombohedral-stacked (R-stacked) transition metal dichalcogenide bilayers exhibit remarkable properties, but their large-area epitaxial growth remains challenging. Here, the authors report the remote epitaxy of centimetre-scale single-crystal R-stacked WS2 bilayer films on sapphire substrates.

Abstract

The advent of 2D ferroelectrics, characterized by their spontaneous polarization states in layer-by-layer domains without the limitation of a finite size effect, brings enormous promise for applications in integrated optoelectronic devices. Comparing with semiconductor/insulator devices, ferroelectric devices show natural advantages such as non-volatility, low energy consumption and high response speed. Several 2D ferrelectric materials have been reported, however, the device implementation particularly for optoelectronic application remains largely hypothetical. Here, we discover the linear electro-optic effect in 2D ferroelectrics and demonstrate electrically tunable 2D ferroelectric metalens. We verified the linear electric-field modulation of light in 2D ferroelectric CuInP₂S₆. The in-plane phase retardation can be continuously tuned by a transverse DC electric field, yielding an effective electro-optic coefficient r _c of 20.28 pm/V. The CuInP₂S₆ crystal exhibits birefringence with the fast axis oriented along its (010) plane. The 2D ferroelectric Fresnel metalens shows efficacious focusing ability with an electrical modulation efficiency of the focusing exceeding 34%. The theoretical analysis uncover the origin of the birefringence and unveil its ultralow light absorption across a wide wavelength range in this non-excitonic system. The van der Waals ferroelectrics enable room-temperature electrical modulation of light and offer the freedom of heterogenous integration with silicon and other material system for highly compact and tunable photonics and metaoptics.

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npj 2D Materials and Applications, Published online: 16 May 2024; doi:10.1038/s41699-024-00473-w

Controlled epitaxy and patterned growth of one-dimensional crystals via surface treatment of two-dimensional templates

Nature Reviews Chemistry, Published online: 16 May 2024; doi:10.1038/s41570-024-00605-2

Intercalation of atoms, ions and molecules is a powerful tool for finely regulating atomically thin, 2D materials. This Review highlights the effects of intercalation in 2D materials and discusses their in situ studies.

This review primarily focuses on elucidating the factors that influence their interfacial growth, with a specific emphasis on the interfacial engineering of heterogeneous reactions, in which MOF-on-MOF heterostructures can be conveniently obtained by using pre-fabricated MOF precursors. These factors are categorized as internal and external elements, including inorganic metals, organic ligands, lattice matching, nucleation kinetics, thermodynamics, etc.

Abstract

Metal–organic frameworks (MOFs), as a subclass of porous crystalline materials with unique structures and multifunctional properties, play a pivotal role in various research domains. In recent years, significant attention has been directed toward composite materials based on MOFs, particularly MOF-on-MOF heterostructures. Compared to individual MOF materials, MOF-on-MOF structures harness the distinctive attributes of two or more different MOFs, enabling synergistic effects and allowing for the tailored design of diverse multilayered architectures to expand their application scope. However, the rational design and facile synthesis of MOF-on-MOF composite materials are in principle challenging due to the structural diversity and the intricate interfaces. Hence, this review primarily focuses on elucidating the factors that influence their interfacial growth, with a specific emphasis on the interfacial engineering of heterogeneous reactions, in which MOF-on-MOF hybrids can be conveniently obtained by using pre-fabricated MOF precursors. These factors are categorized as internal and external elements, encompassing inorganic metals, organic ligands, lattice matching, nucleation kinetics, thermodynamics, etc. Meanwhile, these intriguing MOF-on-MOF materials offer a wide range of advantages in various application fields, such as adsorption, separation, catalysis, and energy-related applications. Finally, this review highlights current complexities and challenges while providing a forward-looking perspective on future research directions.

Complex multimaterial lateral heterostructures of van der Waals semiconductors are fabricated by sequential growth of different multilayer Ge and Sn monochalcogenides. Such designer materials with judiciously placed interfaces provide access to unique properties, exemplified here by the selection of photonic modes with discrete energies in a laterally embedded active layer through Fabry–Perot interference rather than conventional band engineering.

Abstract

Lateral heterostructures combining two multilayer group IV chalcogenide van der Waals semiconductors have attracted interest for optoelectronics, twistronics, and valleytronics, owing to their structural anisotropy, bulk-like electronic properties, enhanced optical thickness, and vertical interfaces enabling in-plane charge manipulation/separation, perpendicular to the trajectory of incident light. Group IV monochalcogenides support propagating photonic waveguide modes, but their interference gives rise to complex light emission patterns throughout the visible/near-infrared range both in uniform flakes and single-interface lateral heterostructures. Here, this work demonstrates the judicious integration of pure and alloyed monochalcogenide crystals into multimaterial heterostructures with unique photonic properties, notably the ability to select photonic modes with targeted discrete energies through geometric factors rather than band engineering. SnS-GeS_1−x Se _x -GeSe-GeS_1−x Se _x heterostructures with a GeS_1−x Se_x active layer sandwiched laterally between GeSe and SnS, semiconductors with similar optical constants but smaller bandgaps, were designed and realized via sequential vapor transport synthesis. Raman spectroscopy, electron microscopy/diffraction, and energy-dispersive X-ray spectroscopy confirm a high crystal quality of the laterally stitched components with sharp interfaces. Nanometer-scale cathodoluminescence spectroscopy provides evidence for a facile transfer of electron–hole pairs across the lateral interfaces and demonstrates the selection of photon emission at discrete energies in the laterally embedded active (GeS_{1− x} Se _x ) part of the heterostructure.

By utilizing a bottom-up approach, meticulous regulation over the epitaxial growth of h-CoO and ZnO on one another is effectively attained, facilitating the fabrication of 3D stereographic structures with customizable geometries. The resulting hybrid nanocrystals exhibit enhanced catalytic performance when contrasted with single-component nanomaterials, primarily due to their distinctive structural characteristics.

Abstract

The rational design of hybrid nanocrystals structures facilitates electronic and energetic communication between different component, which can optimize their specific performance. In this study, an efficient approach for building intricate ZnO@h-CoO nanocomposites and their derivatives is presented, based on a lattice-match/mismatch mechanism. Due to the ultra-low lattice mismatch between ZnO and hexagonal CoO (as low as 0.18%), the h-CoO layer enables epitaxial growth on the ZnO templates, and ZnO can also grow epitaxially outside the CoO layer with ease. Similarly, the thickness of the epitaxial layer and the number of alternating layers can be adjusted arbitrarily. In contrast to h-CoO, the growth of cubic crystalline oxides (such as MnO) on ZnO results in the formation of nanoparticles due to a large mismatch index (following the Volmer–Weber models). Interestingly, when h-CoO is introduced as a further component into the MnO/ZnO composite, the cubic crystalline particles on the surface of the ZnO do not disturb the epitaxial growth of the h-CoO, allowing for the formation of nanocomposites with more components. Furthermore, additional units can be added to the nanocomposite further based on the lattice-match/mismatch mechanism, which is analogous to the building nano-bricks.

A family of conductive van der Waals solid, transition metal carbo-chalcogenide is screened and predicted to be an excellent Li⁺/Na⁺ host, storing near double-layer lithium/sodium and maintaining the structure and voltage, combining with open ion migration paths, holds promises as novel rechargeable battery materials.

Abstract

High-rate lithium/sodium ion batteries or capacitors are the most promising functional units to achieve fast energy storage that highly depends on charge host materials. Host materials with lamellar structures are a good choice for hybrid charge storage hosts (capacitor or redox type). Emerging layered transition metal carbo-chalcogenides (TMCC) with homogeneous sulfur termination are especially attractive for charge storage. Using density functional theory calculations, six of 30 potential TMCC are screened to be stable, metallic, anisotropic in electronic conduction and mechanical properties due to the lamellar structures. Raman, infrared active modes and frequencies of the six TMCC are well assigned. Interlayer coupling, especially binding energies predict that the bulk layered materials can be easily exfoliated into 2D monolayers. Moreover, Ti₂S₂C, Zr₂S₂C are identified as the most gifted Li⁺/Na⁺ anode materials with relatively high capacities, moderate volume expansion, relatively low Li⁺/Na⁺ migration barriers for batteries or ion-hybrid capacitors. This work provides a foundation for rational materials design, synthesis, and identification of the emerging 2D family of TMCC.

This article presents the distinct thickness-related properties of boron nitride nanosheets (BNNSs), encompassing Raman signatures, unique adsorption behavior, mechanical properties, thermal conductivity, and thermal expansion coefficients. It delves into the mechanisms governing thickness effects and explores BNNS applications in surface-enhanced Raman spectroscopy, metal-enhanced fluorescence, and thermal management.

Abstract

Owing to its exceptional properties and wide-ranging potential applications from aerospace to medicine, hexagonal boron nitride (h-BN) has garnered considerable attention over the past decades. Boron nitride nanosheets (BNNSs), atomically thin h-BN, not only inherit most of the outstanding properties of h-BN but also exhibit superior characteristics compared to their bulk counterpart due to their reduced thickness, such as special adsorption behaviors and enhanced thermal conductivity. Furthermore, BNNSs display distinct thickness-dependent properties from graphene and other 2D materials, such as unique mechanical response under indentation. This feature article provides an overview of the thickness-related special properties of BNNSs, primarily derived from mechanically exfoliated h-BN single crystals. These properties span various domains, including Raman signatures, molecule adsorption-induced conformational changes, mechanical properties, thermal conductivity, and thermal expansion coefficients. Moreover, the feature article explores the underlying mechanisms governing these atomic-scale thickness effects. Leveraging their unique properties, the feature article investigates diverse applications of BNNSs, encompassing surface-enhanced Raman spectroscopy, metal-enhanced fluorescence, and isotropic thermal management.

Liquid metal electronic ink (e-ink) that made from gallium, indium, tin, zinc, bismuth or their alloy is 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 via the printing way with low cost at around the room temperature. This leads to the unconventional bottom-up strategy for direct additive manufacture of functional devices. Along this direction, a series of p-n junction diodes, field effect transistors and light-emitting devices have been developed so far. It is clear that the liquid metal printed semiconductor would significantly innovate the classical processes of preparing integrated circuits (IC) and electronic devices. To push forward further progress of this cutting-edge frontier, this article is dedicated to present an overview of liquid metal printed semiconductor. We first introduce the material category of liquid metal semiconductor e-inks and their synthesis approaches. Then the core strategies toward printing semiconductors are systematically outlined. Following that, we summarize the typical printed semiconductor materials and electronic devices thus constructed as well as their potential applications. Lastly, scientific and technical challenges thus raised are interpreted. Perspective in the area is given.

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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.

Abstract

A broad range of chemical transformations driven by catalytic processes necessitate 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 we provide a “non-redox catalysis” strategy wherein the catalytic units were constructed by atomic Fe and B as dual active sites to create tensile force and electric field, which allowed 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 contributed to excellent stability of the active centers, while the generated reactive oxygen species found high efficiency in long-term catalytic pollutant degradation and selective organic oxidation synthesis in aqueous phase. This work offers 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.

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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.

Nature Nanotechnology, Published online: 15 May 2024; doi:10.1038/s41565-024-01675-5

Superionic fluoride dielectrics with a low ion migration barrier are capable of excellent capacitive coupling and are highly compatible with scalable device manufacturing processes for integrated electronics.

Large-area continuous thin films of metastable trigonal Cr₂S₃ are grown by ultralow gas-flow governed dynamic transport methods. The anisotropic SHG response of as-prepared Cr₂S₃ demonstrated effective second-order nonlinearity of 48.0 pm V⁻¹, in which sulfur vacancies and dangling bonds could break the surface central-symmetry and contribute nonlinear optical polarizabilities, providing a new understanding of SHG for nonlayered 2D materials.

Abstract

As for nonlayered 2D polymorphic materials, especially for Cr-based chalcogenides, large-area thin film growth with phase control is considered the most important synthesis challenge for magnetic, electronic, and optoelectronic devices. However, the synthesis methods of large continuous thin films for nonlayered 2D materials are still limited and rarely reported, also for the phase control growth, which is inhibited by isotropic 3D growth and similar Gibbs free energy for different phases. Herein, enhanced mass transport chemical vapor deposition is established to achieve the control synthesis of trigonal Cr₂S₃ thin films, in which the stable boundary layer supplies the continuous reaction species and tunes the reaction kinetics. The trigonal phase formation is confirmed by atomic structure characterization, optical absorption and piezoelectric measurements, demonstrating unique physical properties different from rhombohedral phase. The trigonal Cr₂S₃ thin films show obvious layer independent and dissimilar angle-resolved harmonic generation, indicating the surface broken symmetry that can be understood by the combination of negligible piezoelectric response for bulk. The work presents the large-area synthesized strategy by the modification of mass transport for nonlayered 2D materials with new phase formation and establishes the surface symmetry breaking dominated SHG mechanism for future nonlinear optical materials.

Abstract

Two-dimensional (2D) polarization materials have emerged as promising candidates for meeting the demands of device miniaturization, attributed to their unique electronic configurations and transport characteristics. Although the existing inherent and sliding mechanisms have been increasingly investigated in recent years, strategies for inducing 2D polarization with innovative mechanisms remain rare. In this study, we introduce a novel 2D Janus state by modulating the puckered structure. Combining scanning probe microscopy, transmission electron microscopy, and density functional theory calculations, we realized force-triggered out-of-plane and in-plane dipoles with distorted smaller warping in GeSe. The Janus state is preserved after removing the external mechanical perturbation, which could be switched by modulating the sliding direction. Our work offers a versatile method to break the space inversion symmetry in a 2D system to trigger polarization in the atomic scale, which may open an innovative insight into configuring novel 2D polarization materials.

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Electrochemiluminescence (ECL) is rapidly evolving from an analytical method into an optical microscopy. The orthogonality of the electrochemical trigger and the optical readout distinguishes it from classic microscopy and electrochemical techniques, owing to its near-zero background, remarkable sensitivity, and absence of photobleaching and phototoxicity. In this review, we summarize the recent advances in ECL imaging technology, emphasising original configurations which enable the imaging of biological entities and the improvement of the analytical properties by increasing the complexity and multiplexing of bioassays. Additionally, mapping the (electro)chemical reactivity in space provides valuable information on nanomaterials and facilitates deciphering ECL mechanisms for improving their performances in diagnostics and (electro)catalysis. Finally, we highlight the recent achievements in imaging at the ultimate limits of single molecules, single photons or single chemical reactions, and the current challenges to translate the ECL imaging advances to other fields such as material science, catalysis and biology.