Jiuxiang Dai

Nature Synthesis, Published online: 30 September 2024; doi:10.1038/s44160-024-00666-7

Nature Materials, Published online: 30 September 2024; doi:10.1038/s41563-024-01991-0

Nature Materials, Published online: 30 September 2024; doi:10.1038/s41563-024-01996-9

Nature Materials, Published online: 30 September 2024; doi:10.1038/s41563-024-01990-1

Nature Materials, Published online: 30 September 2024; doi:10.1038/s41563-024-01988-9

Nature Materials, Published online: 30 September 2024; doi:10.1038/s41563-024-02017-5

The present article reports on a single-phase compositionally complex ceramic, i.e., (Ti,Zr,Hf,Nb,Ta)N _x C_1−x , that is synthesized for the first time by employing an organometallic precursor route and using a double ammonolysis process. A multidisciplinary approach is performed to study these compositionally complex nitride and carbonitride systems, including experimental and theoretical investigations.

Compositionally complex transitional metal nitrides are possible candidates for ultra-high temperature usage and are known for their superior properties due to the high configuration entropy. It is often difficult to synthesize pure metal nitrides in bulk, due to significant oxygen contamination; hence, they are synthesized mainly as thin films through magnetron sputtering, chemical vapor deposition or surface nitridation of high entropy alloys. The present article reports on a single-phase compositionally complex ceramic, i.e., (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)N _x C_1−x , that is synthesized for the first time by employing an organometallic precursor route and using a double ammonolysis process. A multidisciplinary approach is performed to study these compositionally complex nitride and carbonitride systems, including experimental and theoretical investigations.

A general strategy for portable preparation of lateral heterostructures using artificial pressure gradients has been designed. Taking violet phosphorus as a case, the controllable pressure gradient generated by diamond anvil cells is utilized to fabricate the violet/blue phosphorus and violet/black phosphorus lateral heterostructures.

Abstract

Hydrostatic conditions are generally pursued in high-pressure research, maintained to prevent the intrinsic pressure gradient on the culets of diamond anvil cells (DACs) from introducing heterogeneity to the structure and physical properties of the regulated materials. Here, a pioneering route to fabricate lateral heterostructures is proposed via artificial pressure gradients intentionally designed in DACs. Under the tailored pressure gradients, different structural phases emerge in distinct parts of the material, resulting in the formation of heterostructures. Harnessing the polymorphic transition nature of violet phosphorus under high pressure, violet/blue and violet/black phosphorus lateral heterostructures with different electrical properties have been successfully prepared by the pressure gradient method. This achievement highlights the potential of artificial pressure gradients as a portable and universal strategy for the fabrication of lateral heterostructures, shedding new light on the preparation and regulation of lateral heterostructures across a wider range of materials.

A substrate-confined sublimation-based vapor deposition method is developed to obtain the hexagonal single crystals of the famous supramolecular crystals of cynuric acid-melamine. A mechanism of three-stage step-growth crystallization is proposed including nucleation, in-plane expansion, and out-of-plane growth. This methodology addresses the longstanding challenge of synthesizing hexagonal CAM single crystals and provides insights for the fabrication of functional organic crystalline materials.

Abstract

Herein, a low-temperature sublimation-based vapor deposition (SVD) method is developed to synthesize hexagonal crystal plates of cyanuric acid-melamine (CAM) with outstanding crystallinity. Through meticulous design of the reaction apparatus and careful selection of source materials, substrate-confined SVD in a tube furnace is explored to grow single crystals of CAM in hexagonal shapes. Additionally, the orientation preference of the (202) facet is revealed, corresponding to the 2D arrangement of the H-bonded network, of single-crystalline plates on surfaces using selected area electron diffraction and X-ray diffraction techniques. By employing atomic force microscopy and scanning electron microscopy for topography characterization, a mechanism of three-stage step-growth crystallization is proposed, including nucleation, in-plane expansion, and out-of-plane growth. Furthermore, it is found that the interactions among melamine molecules in CAM synthesized via SVD are more intense compared to those in CAM synthesized via water-based methods, as evidenced by infrared and photoluminescent spectra studies. Subsequent nanoindentation tests on the (202) facet of CAM single-crystalline plates reveals a reduced modulus and hardness of 12.8 and 0.82 GPa, respectively. This methodology addresses the longstanding challenge of synthesizing hexagonal CAM single crystals and provides valuable insights for the fabrication of functional organic crystalline materials.

Bioinspired morphing swimmers are designed integrating chemical protein motors and photoresponsive liquid crystal networks. This approach gives access to five interchangeable modes of locomotion within a single swimming robot via shape-morphing of the soft structure. The proposed design, which mimics the mechanisms of surface gliding and posture change of semiaquatic insects, offers untethered and orthogonal power and control for small-scale swimming soft robots.

Abstract

Aquatic insects have developed versatile locomotion mechanisms that have served as a source of inspiration for decades in the development of small-scale swimming robots. However, despite recent advances in the field, efficient, untethered, and integrated powering, actuation, and control of small-scale robots remains a challenge due to the out-of-equilibrium and dissipative nature of the driving physical and chemical phenomena. Here, we have designed small-scale, bioinspired aquatic locomotors with programmable deterministic trajectories that integrate self-propelled chemical motors and photoresponsive shape-morphing structures. A Marangoni motor system is developed integrating structural protein networks that self-regulate the release of chemical fuel with photochemical liquid crystal network (LCN) actuators that change their shape and deform in and out of the surface of water. While the diffusion of fuel from the motor system regulates the propulsion, the dissipative photochemical deformation of LCNs provides locomotors with control over the directionality of motion at the air-water interface. This approach gives access to five different but interchangeable modes of locomotion within a single swimming robot via morphing of the soft structure. The proposed design, which mimics the mechanisms of surface gliding and posture change of semiaquatic insects such as water treaders, offers solutions for autonomous swimming soft robots via untethered and orthogonal power and control.

npj 2D Materials and Applications, Published online: 02 October 2024; doi:10.1038/s41699-024-00502-8

The 1D vdW ferroelectric NbOI₃ nanowires possess a high Curie temperature T_C  >  450 K. Impressively, NbOI₃ exhibits a giant second harmonic generation (SHG) effect with a susceptibility up to 1572 pm V⁻¹ at 810 nm, and a further enhanced SHG susceptibility of 5582 pm V⁻¹ under the pressure of 2.06 GPa.

Abstract

The realization of spontaneous ferroelectricity down to the one-dimensional (1D) limit is both fundamentally intriguing and practically appealing for high-density ferroelectric and nonlinear photonics. However, the 1D vdW ferroelectric materials are not discovered experimentally yet. Here, the first 1D vdW ferroelectric compound NbOI₃ with a high Curie temperature T_C  > 450 K and giant second harmonic generation (SHG) is reported. The 1D crystalline chain structure of the NbOI₃ is revealed by cryo-electron microscopy, whereas the 1D ferroelectric order originated from the Nb displacement along the Nb-O chain (b-axis) is confirmed via obvious electrical and ferroelectric hysteresis loops. Impressively, NbOI₃ exhibits a giant SHG susceptibility up to 1572 pm V⁻¹ at a fundamental wavelength of 810 nm, and a further enhanced SHG susceptibility of 5582 pm V⁻¹ under the applied hydrostatic pressure of 2.06 GPa. Combing in situ pressure-dependent X-ray diffraction, Raman spectra measurements, and first-principles calculations, it is demonstrated that the O atoms shift along the Nb─O atomic chain under compression, which can lead to the increased Baur distortion of [NbO₂I₄] octahedra, and hence induces the enhancement of SHG. This work provides a 1D vdW ferroelectric system for developing novel ferroelectronic and photonic devices.

Light: Science & Applications, Published online: 03 October 2024; doi:10.1038/s41377-024-01645-5

Nature Synthesis, Published online: 03 October 2024; doi:10.1038/s44160-024-00657-8

The low-symmetry dielectrics GaInS₃ sparks MoS₂ obvious anisotropy, at the inface of MoS₂/GaInS₃ heterojunction. The anisotropic optical responses are confirmed through polarized Raman and PL spectra. Under dual-gate modulation, MoS₂ FET demonstrates highly adjustable anisotropic conductivity up to 10⁶. Remarkably, the GaInS₃-gated MoS₂ photodetector exhibits a large dichroic ratio (≈167), which greatly promotes its application in polarized photodetection.

Abstract

Low-symmetry structures in van der Waals materials have facilitated the advancement of anisotropic electronic and optoelectronic devices. However, the intrinsic low symmetry structure exhibits a small adjustable anisotropy ratio (1–10), which hinders its further assembly and processing into high-performance devices. Here, a novel 2D anisotropic dielectric, GaInS₃ (GIS), which induces isotropic MoS₂ to exhibit significant anisotropic optical and electrical responses is demonstrated. With the excellent gate modulation ability of 2D GIS (dielectric constant k ∼12), MoS₂ field effect transistor (FET) shows an adjustable conductance ratio from isotropic to anisotropic under dual-gate modulation, up to 10⁶. Theoretical calculations indicate that anisotropy originates from lattice mismatch-induced charge density deformation at the interface. Moreover, the MoS₂/GIS photodetector demonstrates high responsivity (≈4750 A W⁻¹) and a large dichroic ratio (≈167). The anisotropic van der Waals dielectric GIS paves the way for the development of 2D transition metal dichalcogenides (TMDCs) in the fields of anisotropic photonics, electronics, and optoelectronics.

Mechanoresponsive color-changing materials that can reversibly and resiliently change color in response to stress are highly desirable for diverse technologies in optics, sensors, and robots; however, such materials are rarely achieved. This work reports a fatigue-resistant mechanoresponsive color-changing hydrogel that exhibits reversible, resilient, and predictable color changes under mechanical stress, for tactile robots by translating tactile sensations into visual images.

Abstract

Mechanoresponsive color-changing materials that can reversibly and resiliently change color in response to mechanical deformation are highly desirable for diverse modern technologies in optics, sensors, and robots; however, such materials are rarely achieved. Here, a fatigue-resistant mechanoresponsive color-changing hydrogel (FMCH) is reported that exhibits reversible, resilient, and predictable color changes under mechanical stress. At its undeformed state, the FMCH remains dark under a circular polariscope; upon uniaxial stretching of up to six times its initial length, it gradually shifts its color from black, to gray, yellow, and purple. Unlike traditional mechanoresponsive color-changing materials, FMCH maintains its performance across various strain rates for up to 10 000 cycles. Moreover, FMCH demonstrates superior mechanical properties with fracture toughness of 3000 J m⁻², stretchability of 6, and fatigue threshold up to 400 J m⁻². These exceptional mechanical and optical features are attributed to FMCH's substantial molecular entanglements and desirable hygroscopic salts, which synergistically enhance its mechanical toughness while preserving its color-changing performance. One application of this FMCH as a tactile sensoris then demonstrated for vision-based tactile robots, enabling them to discern material stiffness, object shape, spatial location, and applied pressure by translating stress distribution on the contact surface into discernible images.

Here, a viable strategy is demonstrated to regulate the emission of materials by integrating a standard photochromic compound spiropyran into functionalized HOFs, thereby precisely modulating the fluorescence properties. Leveraging the dynamic fluorescence emission, multilevel information encryption applications such as anti-counterfeiting ink, QR code, base code, and time-resolved information storage are successfully showcased.

Abstract

The powerful capability of multi-stimulus-responsive fluorescent hydrogen-bonded organic frameworks (HOFs) to respond to external chemical or physical stimuli in various manners makes them appealing in advanced information encryption. However, it is still a global challenge to manipulate the fluorescence properties finely to achieve dynamic fluorescence properties in the time dimension. Here, a feasible strategy is shown to control the emission of materials by introducing a common SP photochromic compound (1′, 3′, 3′-trimethyl-6-nitro-spiro- [chromene-2, 2′-indoline]) into functionalized HOFs, to finely manipulate the fluorescence properties. Two kinds of HOFs are successfully synthesized by modifying the unbonded carboxylic group of HOFs with Tb³⁺ or 5-hexene-1-ol termed Tb-HOFs and HOF-olefin, respectively. Then, spiropyran is loaded into the Tb-HOFs or HOFs-olefin and dynamic fluorescence emission can be well controlled by changing the lanthanide dopants and light stimulation time. Relying on the dynamic fluorescence emission, the multilevel information encryption including anti-counterfeiting ink, QR code, base code, and time-resolved information storage has been successfully demonstrated, and the security level has been greatly improved. This work opens an avenue for achieving time-resolved information storage technology, where the “time factor” is equivalent to a dynamic key, which introduces countless unpredictable possibilities and makes imitation more challenging.

This review article summarizes the start-of-art of the synthesis and surface chemistry of diamond films and diamond nanostructures, followed by the highlights of their applications in the fields of sensing, energy, catalysis, and biomedicine. The perspectives of synthesis, surface chemistry, and applications of diamond films and nanostructures are also discussed and outlined.

Abstract

Diamond nanomaterials are renowned for their exceptional properties, which include the inherent attributes of bulk diamond. Additionally, they exhibit unique characteristics at the nanoscale, including high specific surface areas, tunable surface structure, and excellent biocompatibility. These multifaceted attributes have piqued the interest of researchers globally, leading to an extensive exploration of various diamond nanostructures in a myriad of applications. This review focuses on non-zero-dimensional (non-0D) diamond nanostructures including diamond films and extended diamond nanostructures, such as diamond nanowires, nanoplatelets, and diamond foams. It delves into the fabrication, modification, and diverse applications of non-0D diamond nanostructures. This review begins with a concise review of the preparation methods for different types of diamond films and extended nanostructures, followed by an exploration of the intricacies of surface termination and the process of immobilizing target moieties of interest. It then transitions into an exploration of the applications of diamond films and extended nanostructures in the fields of biomedicine and electrochemistry. In the concluding section, this article provides a forward-looking perspective on the current state and future directions of diamond films and extended nanostructures research, offering insights into the opportunities and challenges that lie ahead in this exciting field.

This experimental work focuses on the design and fabrication of a basic module for integrated thermoelectric devices based on a large number of interconnected monocrystalline silicon nanobeams, very tall (>1 µm) and thin (less than 200 nanometers). The proposed structure shows high mechanical stability and very good values of deliverable power per unit area.

Abstract

The strong reduction of thermal conductivity with respect to bulk silicon makes nanostructured silicon one of the best materials for highly efficient direct conversion of heat into electrical power and vice-versa. The widespread technologies for the integration of silicon devices can be used to define on-chip micro thermoelectric generators (scavengers); similar structures could also be used for precise and well-localized cooling through the reverse process of heat pumping. However, the road to the fabrication of integrated thermal energy scavengers or cooler, based on silicon, is still very long. In this work, the design and the fabrication process of on-chip thermoelectric devices based on a large number of interconnected monocrystalline silicon nanobeams, very tall (>1 µm) and thin (less than 200 nanometers), arranged in large areas combs is shown. The small width of the nanobeams gives a reduced thermal conductivity, and the height perpendicular to the substrate allows the definition of a highly dense collection of nanostructures. The total cross-section is far broader than that of other nanostructures, a characteristic that guarantees both mechanical stability and larger deliverable power per unit area.

Nature Photonics, Published online: 27 September 2024; doi:10.1038/s41566-024-01529-5

Author(s): A. D. Kokovin, V. Yu. Kachorovskii, and I. S. Burmistrov

We develop the microscopic theory for the attenuation of out-of-plane phonons in stressed flexible two-dimensional crystalline materials. We demonstrate that the presence of nonzero tension strongly reduces the relative magnitude of the attenuation and, consequently, results in parametrical narrowin…

[Phys. Rev. Lett. 133, 136203] Published Fri Sep 27, 2024

Author(s): Ying Xiong, Mark S. Rudner, and Justin C. W. Song

Screening is a ubiquitous phenomenon through which the polarization of bound or mobile charges tends to reduce the strengths of electric fields inside materials. Here, we show how photoexcitation can be used as a knob to transform conventional out-of-plane screening into antiscreening—the amplificat…

[Phys. Rev. Lett. 133, 136901] Published Fri Sep 27, 2024