Jing Zhang

Presenting a comprehensive review on recent advancements in strain-engineered 2D transition metal dichalcogenides (TMDs). This review delves into precision tuning of valley physics through strain engineering, elucidating mechanisms and connections between strain-induced modifications and optoelectronic characteristics. It offers insights into future directions of valley-straintronics, underscoring the significant promise of valley-strain engineering in TMDs for fundamental studies and practical applications.

Abstract

2D transition metal dichalcogenides (TMDs) have emerged as a novel class of semiconductors with promising applications in optoelectronics, owing to their rich and tunable valley fine structure, known as valleytronics. Strain engineering in TMDs presents opportunities to tailor their valley fine structures and band alignment, which greatly expands the potential to investigate their intrinsic properties and improve device performance, thus opening a new field of straintronics. In this review, recent advances in strain-engineered 2D TMDs are summarized, with a focus on new phenomena and applications enabled by precision tuning of valley physics. The underlying mechanisms and connections are delineated between strain-induced modifications to the valley fine structures based on intravalley, intervalley, and interlayer band alignment in single and heterostructure TMDs. These insights allow targeted strain control strategies to be devised for optimizing optoelectronic characteristics. This review provides perspectives and guidance on the future directions of valley-straintronics and flexible 2D optoelectronics using TMDs, highlighting the substantial promise of valley-strain engineering in TMDs for fundamental valley physics studies as well as practical device applications.

The van der Waals (vdW) force has been regarded as a versatile and universal potential. Nevertheless, whether vdW force can be used as an attractive potential for the crystallization of colloids remains to be proven. Here, it is shown that the implementation of gold cores into silica colloids can reconfigure vdW force to optimal range in terms of colloidal crystallizations.

Abstract

A general guiding principle for colloidal crystallization is to tame the attractive enthalpy such that it slightly overwhelms the repulsive interaction. As-synthesized colloids are generally designed to retain a strong repulsive potential for the high stability of suspensions, encoding appropriate attractive potentials into colloids has been key to their crystallization. Despite the myriad of interparticle attractions for colloidal crystallization, the van der Waals (vdW) force remains unexplored. Here, it is shown that the implementation of gold cores into silica colloids and the resulting vdW force can reconfigure the pair potential well depth to the optimal range between −1 and −4 k_BT at tens of nanometer-scale colloidal distances. As such, colloidal crystals with a distinct liquid gap can be formed, which is evidenced by photonic bandgap-based diffractive colorization.

A negative-differential-resistance (NDR) device featuring a junctionless vdW channel. The approach for inducing the NDR phenomenon revolves around selectively inhibiting carrier transport, a result accomplished by creating a partial potential barrier within the junctionless channel. To showcase the utility of the junctionless NDR device for a ternary hardware neural network, its practical application is presented by configuring ternary logic circuits.

Abstract

Negative-differential-resistance (NDR) devices offer a promising pathway for developing future computing technologies characterized by exceptionally low energy consumption, especially multivalued logic computing. Nevertheless, conventional approaches aimed at attaining the NDR phenomenon involve intricate junction configurations and/or external doping processes in the channel region, impeding the progress of NDR devices to the circuit and system levels. Here, an NDR device is presented that incorporates a channel without junctions. The NDR phenomenon is achieved by introducing a metal-insulator-semiconductor capacitor to a portion of the channel area. This approach establishes partial potential barrier and well that effectively restrict the movement of hole and electron carriers within specific voltage ranges. Consequently, this facilitates the implementation of both a ternary inverter and a ternary static-random-access-memory, which are essential components in the development of multivalued logic computing technology.

Highly efficient room-temperature nonvolatile magnetic switching by current is realized in a single-material device based on vdW ferromagnet Fe₃GaTe₂. This result is mainly caused by the spin-orbit-torque effect in Fe₃GaTe₂ itself. Moreover, the switching current density and the power dissipation are several orders of magnitude smaller than those in conventional spin-orbit-torque devices of magnet/heavy-metal heterostructures.

Abstract

Effectively tuning magnetic state by using current is essential for novel spintronic devices. Magnetic van der Waals (vdW) materials have shown superior properties for the applications of magnetic information storage based on the efficient spin torque effect. However, for most of known vdW ferromagnets, the ferromagnetic transition temperatures lower than room temperature strongly impede their applications and the room-temperature vdW spintronic device with low energy consumption is still a long-sought goal. Here, the highly efficient room-temperature nonvolatile magnetic switching is realized by current in a single-material device based on vdW ferromagnet Fe₃GaTe₂. Moreover, the switching current density and power dissipation are about 300 and 60000 times smaller than conventional spin-orbit-torque devices of magnet/heavy-metal heterostructures. These findings make an important progress on the applications of magnetic vdW materials in the fields of spintronics and magnetic information storage.

Nature, Published online: 06 March 2024; doi:10.1038/s41586-024-07058-z

We leverage advances in integrated photonics to generate low-noise microwaves with an optical frequency division architecture that can be low power and chip integrated.

Surprising coherently coupled elastodynamics is observed between a VO₂ film exhibiting an insulator-to-metal transition (IMT) and a TiO₂ substrate that   also exhibits an IMT-like response in a micrometers deep surface layer, reveals by spatiotemporal X-ray diffraction microscopy. Phase-field model points to native oxygen vacancy defects that respond to electric fields, a promising direction for neuromorphic computing.

Abstract

The drive toward non-von Neumann device architectures has led to an intense focus on insulator-to-metal (IMT) and the converse metal-to-insulator (MIT) transitions. Studies of electric field-driven IMT in the prototypical VO₂ thin-film channel devices are largely focused on the electrical and elastic responses of the films, but the response of the corresponding TiO₂ substrate is often overlooked, since it is nominally expected to be electrically passive and elastically rigid. Here, in-operando spatiotemporal imaging of the coupled elastodynamics using X-ray diffraction microscopy of a VO₂ film channel device on TiO₂ substrate reveals two new surprises. First, the film channel bulges during the IMT, the opposite of the expected shrinking in the film undergoing IMT. Second, a microns thick proximal layer in the substrate also coherently bulges accompanying the IMT in the film, which is completely unexpected. Phase-field simulations of coupled IMT, oxygen vacancy electronic dynamics, and electronic carrier diffusion incorporating thermal and strain effects suggest that the observed elastodynamics can be explained by the known naturally occurring oxygen vacancies that rapidly ionize (and deionize) in concert with the IMT (MIT). Fast electrical-triggering of the IMT via ionizing defects and an active “IMT-like” substrate layer are critical aspects to consider in device applications.

Using a combination of femtosecond electron diffraction, structure factor calculations, and TDDFT-MD simulations, the local disorder and local anharmonicity in thermoelectric SnSe are identified exclusively, indicating a glass-like thermal transport channel. The use of femtosecond electron diffraction is demonstrated to detect nonequilibrium structural dynamics in crystalline-disordered materials and reveal the intrinsic local disorder and local anharmonicity with femtosecond-picometer temporospatial resolution.

Abstract

In addition to long-range periodicity, local disorder, with local structures deviating from the average lattice structure, dominates the physical properties of phonons, electrons, and spin subsystems in crystalline functional materials. Experimentally characterizing the 3D atomic configuration of such a local disorder and correlating it with advanced functions remains challenging. Using a combination of femtosecond electron diffraction, structure factor calculations, and time-dependent density functional theory molecular dynamics simulations, the static local disorder and its local anharmonicity in thermoelectric SnSe are identified exclusively. The ultrafast structural dynamics reveal that the crystalline SnSe is composed of multiple locally correlated configurations dominated by the static off-symmetry displacements of Sn (≈0.4 Å) and such a set of locally correlated structures is termed local disorder. Moreover, the anharmonicity of this local disorder induces an ultrafast atomic displacement within 100 fs, indicating the signature of probable THz Einstein oscillators. The identified local disorder and local anharmonicity suggest a glass-like thermal transport channel, which updates the fundamental insight into the long-debated ultralow thermal conductivity of SnSe. The method of revealing the 3D local disorder and the locally correlated interactions by ultrafast structural dynamics will inspire broad interest in the construction of structure–property relationships in material science.

This study reports a “dynamic” wrinkling system with controllable polymer interaction networks. By regulating the viscoelasticity of polymer interaction networks, the wavelength and the relaxation rate of the wrinkles can be controlled. Consequently, dynamic wrinkling anti-counterfeiting patterns and time-resolved multistage information encryption are achieved, which can be further utilized to develop a practical encryption label.

Abstract

As counterfeit techniques continue to evolve, ensuring the security of conventional “static” encryption methods becomes increasingly challenging. Here, the viscoelasticity-controlled relaxation is introduced for the first time in a bilayer wrinkling system by regulating the density of hydrogen bond networks in polymer to construct a “dynamic” encryption material. The wrinkling surface can manipulate light during the dynamic relaxation process, exhibiting three stages with frosted glass, structural color, and mirror reflection. By regulating the viscoelasticity of skin layer through UV irradiation, the wavelength and the relaxation rate of the wrinkles can be controlled. As a result, dynamic wrinkling anti-counterfeiting patterns and time-resolved multistage information encryption are achieved. Crucially, the encryption material is developed as an anti-counterfeiting label for packing boxes in daily applications, allowing the encrypted information to be activated manually and identified by naked eyes, surpassing the existing time-resolved encryption materials in utilization potential. Besides, the dynamic hydrogen bond networks are extended to various dynamic interaction networks, demonstrating the versatility of the dynamic encryption strategy. This work not only provides an additional dimension for dynamic information encryption in daily practical use, but also offers theoretical guidance for the development of advanced optical anti-counterfeiting and smart display materials in the future.

Here, a time-dependent information encryption model from a liquid crystalline polymer with a programmable glass transition temperature (T _g) and gradually adjustable fluorescence is presented. The programmable T _g is achieved by adjusting the degree of order of the materials via a configuration interconversion of spiropyran-based materials (SPBMs), and the gradually adjustable fluorescence is achieved via a fluorescence resonance energy transfer effect.

Abstract

Time-dependent dynamic information encryption technology is a promising approach to enhancing the security and complexity of information transmission. Herein, a time-dependent information encryption model from a liquid crystalline polymer (LCP) film with a programmable glass transition temperature (T _g) and gradually adjustable fluorescence is demonstrated. The programmable T _g is achieved by adjusting the degree of order of the LC molecules via a configuration interconversion of spiropyran-based materials (SPBMs), which can convert between a V-shaped colorless spiro (SP) and a rodlike dark-colored merocyanine (MC) form. An LCP film obtained by visible light polymerization exhibits a lower T _g than UV light, because the SPBM molecules keep different configurations in the two films. By adjusting the ratio of two isomerization forms of SPBM molecules during the polymerization process, the T _g values of LCP films can change from 11.6 °C to 31.1 °C. Based on the isomerization rate of SPBM in the LCP films with different T _g, time-dependent information encryption is successfully achieved.

This study presents a 3D stackable vertical-sensing electrochemical random-access memory (VS-ECRAM) utilizing the low-temperature (200 °C) atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) process. The AP-PECVD-synthesized WS₂ drain electrode, which also serves as an ion-barrier layer, enables near-ideal linearity in the synaptic weight update behavior, excellent cycling reliability and variability, and 3D multi-stacking process compatibility.

Abstract

Ion-based electrochemical random-access memory (ECRAM) is proposed for synaptic applications owing to its promising characteristics that have the potential to accelerate data processing through neuromorphic systems. However, attaining ideal synaptic functionalities and constructing high-density vertical synapse arrays are challenging due to issues related to uncontrolled ion migration and constraints in 3D multi-stacking. Here, a breakthrough using 3D stackable Li ion-based vertical-sensing ECRAM (VS-ECRAM) is presented with an ion-permeable ultrathin WS₂ electrode synthesized through low-temperature (200 °C) atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD). The direct AP-PECVD of the WO_x channel layer induces WS₂ formation in the surface region, which exhibits sufficient electrical conductivity to function as an electrode. By utilizing the WS₂ electrode as an ion-barrier layer in the VS-ECRAM synapse, excellent weight update linearity and cycling variability are achieved due to the finely controlled ion migration. Furthermore, a two-layer stacked 3D VS-ECRAM is successfully fabricated through the vertical WS₂ formation, and independent weight updates without any disturbance are confirmed. Finally, a high pattern recognition accuracy of 95.22% is obtained using a multi-layer perceptron-based neural network. Therefore, the proposed 3D stackable WS₂-based VS-ECRAM exhibits a strong potential for application in high-density neuromorphic devices with excellent synaptic performances.

Using inherent atomic properties in the periodic table, a concise descriptor is proposed for rapidly determining dipole moment and band alignment in 2D Janus TMDCs, facilitating the rational design of 2D electronic devices.

Abstract

The dipole moment (µ) is a critical parameter in Janus structures, influencing band alignments and carrier transmissions. However, evaluating µ in 2D Janus layers is challenging due to the vast number of structures and the inefficiency of Kelvin probe force microscopy. Using the recently developed 2D Janus transition-metal dichalcogenides (TMDCs) as a prototype, a descriptor is proposed based on fundamental parameters (atomic number and atomic radii) to investigate the relationship between atomic structures and µ. By constructing 621 structural models, this descriptor is applicable from monolayers to three-layers. By considering shielding effect of terminal atoms, the performance of the descriptor has been significantly enhanced, resulting in a description accuracy of 94.6% for all TMDC systems. Based on this descriptor, the Anderson's Rule (AR) model can be extended to Janus bilayers in simulating band alignments, resulting in a substantial improvement in accuracy from 20.0% to 90.8%. This development holds crucial importance in screening Janus self-doping P-N junctions. The work provides an efficient descriptor based on inherent atomic properties for rapid determining dipole moment and band alignment in 2D Janus TMDCs, accelerating the design of devices with built-in electronic field structures.

Recent progress on the influence of pressure on perovskite materials and devices is reviewed. Based on the mechanism of influence, the pressure effect can be divided into six categories: crystal densification, crystal orientation, crystal size, bond length, bond angle, bandgap, phase transition, and amorphous phase. Finally, prospects for developing new perovskite structures and devices under pressure are presented.

Abstract

As a fundamental thermodynamic parameter, pressure serves as an effective tool to control the structures and properties of functional materials. To date, numerous pressure-engineering methods have been introduced to enhance perovskite structures and devices. This paper comprehensively reviews the advances in understanding the effects of pressure on perovskite materials and devices, encompassing both low and high-pressure influences. These effects are categorized into six distinct groups based on their underlying mechanisms, detailing the evolution of perovskite structures from macroscopic to microscopic levels, and exploring the interplay between these structures and their functional characteristics. Finally, the current challenges and offer insights into the future prospects for harnessing pressure effects to further develop perovskite structures, properties, and devices are assessed.

Leveraging from thickness control methodology, vertical ferroelectric polarization switching is recorded on a 6 nm thick specimen probed by a piezoresponse force microscopy. The ferroelectric origin is uncovered by first-principles density-functional theory calculations. Bi₂O₂Se-based field-effect transistor demonstrated an unprecedented current on–off ratio of 10⁸ and carrier mobility of 131 cm² V⁻¹ s⁻¹. This work manifests the feasibility of 2D Bi₂O₂Se for next-generation electronics.

Abstract

The amelioration of atomically thin ferroelectric materials is imperative for next-generation outperformed two-dimensional (2D) electronics, which is elusive by their bulk counterparts. These remarkable materials’ ferroelectric and piezoelectric features are the fundamental urges in optoelectronics, electronics, and energy harvesting. In this work, 2D ferroelectric Bi₂O₂Se flakes have been synthesized using a modified chemical vapor deposition technique. The 6 nm thick Bi₂O₂Se flake provides a robust ferroelectric switching under an applied voltage of ±10 V by piezoresponse force microscopy, further confirmed by first principles. Leveraging the successful growth, the high-quality Bi₂O₂Se flakes permit the fabrication of a field-effect transistor (FET) with state-of-the-art performance. The FET device rewards a high current on–off ratio of 10⁸ and field effect mobility of almost 131 cm² V⁻¹ s⁻¹, owing to the small carrier effective mass of 0.2 m₀. Combined, the electric field-induced local polarization of ferroelectric switching and unprecedented device performance of Bi₂O₂Se semiconductors are certified for their utilization in advanced nanoelectronics and miniaturization of multifunctional devices with multifunctionalities.

Combining laser scribing techniques and strain engineering techniques, a laser-guided self-assembly strategy is developed to manufacture 3D micro-rolls from thin films. This dry-release strategy is highly scalable and viable in the atmosphere, and achieves precise control of self-assembly behavior (including self-rolling areas, curvatures, orientations, and sizes) by itself (no pre-patterning or post-drying required), outperforming all the existing reported self-assembly methods.

Abstract

Advanced manufacturing techniques offer tremendous potential in electronics, photonics, and biomedicine. Self-assembly is a powerful strategy for creating three-dimensional (3D) artificial structures, but existing thin film release techniques have limitations in the relatively complex processes. Herein, a localized laser scribing strategy is proposed to guide the self-assembly of two-dimensional thin films into 3D microstructures. It is revealed that laser-induced heating and momentum can release thin films and roll them into various microstructures. Uniquely, this method allows accurate control of shapes, curvatures, orientations, and sizes for the fabricated rolls. This is a one-step strategy with no pre-patterning or post-drying required. The proposed method represents a significant improvement over existing self-assembly techniques and may enrich the thin film self-assembly materials and applications. As proof of concept, the prepared gold micro-rolls are demonstrated as implanted stents in porcine arteries with impressive flexibility. This study provides a new approach to creating 3D microstructures with simplicity and high repeatability and has significant implications for the future of advanced manufacturing, especially in emerging miniaturized applications, such as invasive robotics, minimized drug delivery, implanted batteries, and nanophotonics.

Extremely high-density, physically unclonable cryptographic keys are demonstrated by using stochastic nanoscale ferroelectric domain polarizations in Aurivillius ferroelectric CaBi₂Nb₂O₉ as a robust source of physical unclonable entropy. Reconfiguration of the ferroelectric cryptographic keys with no correlation is facilitated by voltage pulse operations. Consequently, a high data density of 435 Gbit is achievable within a miniaturized area of 1 um².

Abstract

In the era of information, emerging hardware security primitives, i.e., hardware random number generators and physically unclonable functions, hold profound promise for the establishment of exceptionally secure network information systems. Nonetheless, these potential solutions are constrained by inherent drawbacks, including the need for additional error correction circuits or algorithms, heightened susceptibility to environmental interference, and limited data density. This paper demonstrates the extremely high-density, physical-unclonable cryptographic keys by harnessing stochastically ferroelectric domain polarizations in Aurivillius ferroelectric material CaBi₂Nb₂O₉ (CBNO). Ferroelectric polarization of CBNO nanodomains can serve as a robust source of physical unclonable entropy. Through the application of high-speed voltage pulses, the inherent randomness of ferroelectric polarizations can be enhanced, thereby yielding cryptographic keys characterized by remarkable uniformity, uniqueness, and negligible environmental sensitivity. More importantly, the voltage pulse operations facilitate the configurability of the ferroelectric cryptographic keys with no correlation. An unprecedented data density of 435 Gbit µm⁻² is therefore achievable with a miniaturized CBNO of less than 1 um². Notably, the reconfigured keys successfully pass the National Institute of Standards and Technology random number tests without requiring additional post-processing steps. Emanating from the inherent attributes of the material, these high-density ferroelectric keys confer intrinsic advantages to information security, evincing substantial resistance to duplication or cloning.

Recent progress in the research and development of 2D atomic layers for CO₂ photoreduction is reviewed. The advantages and features of 2D atomic layers for CO₂ photoreduction are presented. The classification, controlled fabrication, and formation mechanism of various materials are introduced. Different strategies are employed to further boost the CO₂ reduction performance of 2D atomic layers.

Abstract

Artificial photosynthesis can convert carbon dioxide into high value-added chemicals. However, due to the poor charge separation efficiency and CO₂ activation ability, the conversion efficiency of photocatalytic CO₂ reduction is greatly restricted. Ultrathin 2D photocatalyst emerges as an alternative to realize the higher CO₂ reduction performance. In this review, the basic principle of CO₂ photoreduction is introduced, and the types, advantages, and advances of 2D photocatalysts are reviewed in detail including metal oxides, metal chalcogenides, bismuth-based materials, MXene, metal-organic framework, and metal-free materials. Subsequently, the tactics for improving the performance of 2D photocatalysts are introduced in detail via the surface atomic configuration and electronic state tuning such as component tuning, crystal facet control, defect engineering, element doping, cocatalyst modification, polarization, and strain engineering. Finally, the concluding remarks and future development of 2D photocatalysts in CO₂ reduction are prospected.

The crystallization pathway to either α −Ga or β −Ga can be effectively engineered by a universally existing critical annealing temperature, which non-trivially depends on the droplet size at micron-scale. This polymorph selection mechanism is suggested to be highly relevant to the capability of forming covalent bonds linked to the crystallization product in the equilibrium supercooled liquid.

Abstract

As the most popular liquid metal (LM), gallium (Ga) and its alloys are emerging as functional materials due to their unique combination of fluidic and metallic properties near room temperature. As an important branch of utilizing LMs, micro- and submicron-particles of Ga-based LM are widely employed in wearable electronics, catalysis, energy, and biomedicine. Meanwhile, the phase transition is crucial not only for the applications based on this reversible transformation process, but also for the solidification temperature at which fluid properties are lost. While Ga has several solid phases and exhibits unusual size-dependent phase behavior. This complex process makes the phase transition and undercooling of Ga uncontrollable, which considerably affects the application performance. In this work, extensive (nano-)calorimetry experiments are performed to investigate the polymorph selection mechanism during liquid Ga crystallization. It is surprisingly found that the crystallization temperature and crystallization pathway to either α −Ga or β −Ga can be effectively engineered by thermal treatment and droplet size. The polymorph selection process is suggested to be highly relevant to the capability of forming covalent bonds in the equilibrium supercooled liquid. The observation of two different crystallization pathways depending on the annealing temperature may indicate that there exist two different liquid phases in Ga.

Nature Photonics, Published online: 01 March 2024; doi:10.1038/s41566-024-01400-7

A transparent ceramic phosphor based on Cr3+-doped MgO offers a route to a powerful broadband near-infrared light source.

Nature Communications, Published online: 02 March 2024; doi:10.1038/s41467-024-46246-3

Parallel information transmission components and hardware strategies are still lacking in neural networks. Here, the authors propose a strategy to use light emitting memristors with negative ultraviolet photoconductivity and intrinsic parallelism to construct direct information cross-layer modules.

A seeded growth technique is developed for crystallizing large-scale 2D CrTe₂ films on amorphous SiN _x /Si substrates with a low thermal budget. Grain boundaries, intrinsic ferromagnetism, and magnetic–electrical behavior of 2D CrTe₂ magnets are controlled through crystallinity engineering. This work paves the way for large-scale batch manufacturing of practical magneto–electronic and spintronic devices, heralding a new era of technological innovation.

Abstract

2D van der Waals (vdW) magnets open landmark horizons in the development of innovative spintronic device architectures. However, their fabrication with large scale poses challenges due to high synthesis temperatures (>500 °C) and difficulties in integrating them with standard complementary metal-oxide semiconductor (CMOS) technology on amorphous substrates such as silicon oxide (SiO₂) and silicon nitride (SiN _x ). Here, a seeded growth technique for crystallizing CrTe₂ films on amorphous SiN _x /Si and SiO₂/Si substrates with a low thermal budget is presented. This fabrication process optimizes large-scale, granular atomic layers on amorphous substrates, yielding a substantial coercivity of 11.5 kilo-oersted, attributed to weak intergranular exchange coupling. Field-driven Néel-type stripe domain dynamics explain the amplified coercivity. Moreover, the granular CrTe₂ devices on Si wafers display significantly enhanced magnetoresistance, more than doubling that of single-crystalline counterparts. Current-assisted magnetization switching, enabled by a substantial spin–orbit torque with a large spin Hall angle (85) and spin Hall conductivity (1.02 ×  10⁷ ℏ/2e  Ω⁻¹  m⁻¹), is also demonstrated. These observations underscore the proficiency in manipulating crystallinity within integrated 2D magnetic films on Si wafers, paving the way for large-scale batch manufacturing of practical magnetoelectronic and spintronic devices, heralding a new era of technological innovation.

Optoelectronic Memristors

In article number 2307393, Fucai Liu, Deen Gu, Kah-Wee Ang, and co-workers present an overview of the fundamental performance, mechanisms, structure designs, applications, and integration roadmap of optoelectronic memristors. By establishing connections between materials, multilayer optoelectronic memristor units, and monolithic optoelectronic integrated circuits, this review provides insights into emerging technologies and prospects expected to drive innovation and widespread adoption in neuromorphic optoelectronics applications.

1D ternary van der Waals (vdWs) material, Mo₆Se₂I₈ with non-centrosymmetric characteristics and strong optical anisotropy, exhibits weak interchain coupling. Taking advantage of this weak vdWs coupling characteristic, the in situ probe exfoliation of the 1D Mo₆Se₂I₈ is achieved by using a nanoprobe in a scanning electron microscope (SEM), obtaining ultrathin Mo₆Se₂I₈ molecular chains.

Abstract

van der Waals (vdWs) interchain coupling is a unique feature of 1D vdWs materials, where strong vdWs coupling in 1D vdWs materials leads to the thickness-dependent physical properties, while weak vdWs coupling can preserve the single-chain property even in their thick counterparts. Different from 2D vdWs materials, due to their nanoscale widths, identifying and producing ultrathin 1D molecular chains are challenging, severely limit their device applications. Thus, looking for novel 1D vdWs materials with weak interchain coupling is crucial. In this paper, the authors report that the 1D ternary vdWs material, Mo₆Se₂I₈ with non-centrosymmetric characteristic and strong optical anisotropy, exhibits weak interchain coupling. On one hand, the density functional theory (DFT) calculations theoretically demonstrate its thickness-independent electronic structure, negligible interchain differential charge density, and weak cleavage energy as low as 0.256 J m⁻². On the other hand, the thickness-independent work function and low first-order temperature coefficient of −0.0030 cm⁻¹ K⁻¹ further experimentally confirm its weak interchain coupling. Moreover, taking advantage of this weak vdWs coupling characteristic, the in situ exfoliation of the Mo₆Se₂I₈ nanowires is achieved by using a nanoprobe in a scanning electron microscope (SEM), obtaining ultrathin molecular chains with a thickness of ≈1.2 nm.

This research introduces a novel approach to address challenges in controlling functionalized microrobots. By using an asymmetric magnetic texture resembling a lateral ladder, termed the “railway track,” precise unidirectional movement is achieved, enabling versatile microrobot manipulation. This concept allows for complex tasks such as targeted collection, controlled transport, and local mixing, advancing micro-robotics beyond traditional magnetic field-based control methods.

Abstract

Functionalized microrobots, which are directionally manipulated in a controlled and precise manner for specific tasks, face challenges. However, magnetic field-based controls constrain all microrobots to move in a coordinated manner, limiting their functions and independent behaviors. This article presents a design principle for achieving unidirectional microrobot transport using an asymmetric magnetic texture in the shape of a lateral ladder, which the authors call the “railway track.” An asymmetric magnetic energy distribution along the axis allows for the continuous movement of microrobots in a fixed direction regardless of the direction of the magnetic field rotation. The authors demonstrated precise control and simple utilization of this method. Specifically, by placing magnetic textures with different directionalities, an integrated cell/particle collector can collect microrobots distributed in a large area and move them along a complex trajectory to a predetermined location.  The authors can leverage the versatile capabilities offered by this texture concept, including hierarchical isolation, switchable collection, programmable pairing, selective drug-response test, and local fluid mixing for target objects. The results demonstrate the importance of microrobot directionality in achieving complex individual control. This novel concept represents significant advancement over conventional magnetic field-based control technology and paves the way for further research in biofunctionalized microrobotics.

A metal–organic framework consisting of Eu³⁺ and 1,3,5-benzenetricarboxylic acid exhibits an eightfold enhancement in luminescence intensity upon doping with Y³⁺ and Ca²⁺ ions. This emission enhancement correlates with changes in the Eu³⁺ local electric field and is consistent with significant changes in HOMO and LUMO levels. The doped MOFs are successfully used for photonic barcoding and fingerprinting applications.

Abstract

Emission from metal–organic frameworks (MOFs) made from Eu³⁺ and 1,3,5-benzenetricarboxylic acid (BTC) is enhanced eightfold by doping with Y³⁺ and Ca²⁺ ions. The Ca²⁺ ions are shown to substitute into the MOFs, and the MOFs structure is shown to be retained at high Y³⁺ doping levels. The emission enhancement is shown to be associated with variations in the local electric field at the Eu³⁺ centers in the MOFs. Calculations indicate that the HOMO and LUMO levels vary considerably with both Y³⁺ doping and with low-level Ca²⁺ doping. These then modulates Eu³⁺ concentration quenching, ligand-metal energy transfer processes, and the local electric field at the Eu³⁺ centers, qualitatively accounting for the primary observed features. For UV excitation (250, 295, and 393 nm, respectively), the greatest emission enhancement comes from the doped MOFs with 10% Eu³⁺, 89% Y³⁺, and 1% Ca²⁺. In a photonic barcode application, the doped MOFs are shown to facilitate increased information storage density, and in a fingerprinting application, they are displayed to lead to higher photostability and reduced materials demand.

This review summarizes the pioneering morphological variations among RE-doped fluoride nanoparticles, impacting applications such as anti-counterfeiting, temperature sensing, and photodynamic therapy. Exploring distinctive forms, including hollow, dumbbell, and peasecod-like nanoparticles, unveils potential applications. Future research in the field hinges on advanced techniques to customize nanoparticle shape, enhancing aggregation an targeted modification.

Abstract

The advanced design of rare-earth-doped (RE-doped) fluoride nanoparticles has expanded their applications ranging from anticounterfeiting luminescence and contactless temperature measurement to photodynamic therapy. Several recent studies have focused on developing rare morphologies of RE-doped nanoparticles. Distinct physical morphologies of RE-doped fluoride materials set them apart from contemporary nanoparticles. Every unusual structure holds the potential to dramatically improve the physical performance of nanoparticles, resulting in a remarkable revolution and a wide range of applications. This comprehensive review serves as a guide offering insights into various uniquely structured nanoparticles, including hollow, dumbbell-shaped, and peasecod-like forms. It aims to cater to both novices and experts interested in exploring the morphological transformations of nanoparticles. Discovering new energy transfer pathways and enhancing the optical application performance have been long-term challenges for which new solutions can be found in old papers. In the future, nanoparticle morphology design is expected to involve more refined microphysical methods and chemically-induced syntheses. Targeted modification of nanoparticle morphology and the aggregation of nanoparticles of various shapes can provide the advantages of different structures and enhance the universality of nanoparticles.

Nature Synthesis, Published online: 29 February 2024; doi:10.1038/s44160-024-00488-7

A chemist-intuited atomic robotic probe is developed that enables autonomous site-selective manipulation of magnetic nanographenes with atomic precision and aids in reaction mechanism elucidation through the incorporation of learned knowledge and artificial intelligence, leading to the intelligent synthesis of these materials.

Nature Materials, Published online: 28 February 2024; doi:10.1038/s41563-024-01830-2

Single-crystal black phosphorus nanoribbons are grown uniformly on insulating substrates by chemical vapour transport growth with black phosphorus nanoparticles as seeds, demonstrating potential for application in nanoelectronic devices and the exploration of the exotic physics in black phosphorus.

Nature, Published online: 29 February 2024; doi:10.1038/d41586-024-00597-5

Advances in materials science and sensing could deliver robots that can mend themselves and feel pain.