Jiuxiang Dai

Nature Communications, Published online: 01 March 2024; doi:10.1038/s41467-024-45952-2

Nature Electronics, Published online: 01 March 2024; doi:10.1038/s41928-024-01129-9

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 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.

The electrodeposition technique can be used to design Cu₂O hierarchical microarchitectures. Simply varying the overpotential induces the growth of a new building unit on the preformed ones, giving rise to the formation of complex hierarchical microarchitectures. Cl⁻ ions are used to adjust growth rates of {100} facets, further strengthening the capability of the electrodeposition technique.

Abstract

Rational morphology control of inorganic microarchitectures is important in diverse fields, requiring precise regulation of nucleation and growth processes. While wet chemical methods have achieved success regarding the shape-controlled synthesis of micro/nanostructures, accurately controlling the growth behavior in real time remains challenging. Comparatively, the electrodeposition technique can immediately control the growth behavior by tuning the overpotential, whereas it is rarely used to design complex microarchitectures. Here, the electrochemical design of complex Cu₂O microarchitectures step-by-step by precisely controlling the growth behavior is demonstrated. The growth modes can be switched between the thermodynamic and kinetic modes by varying the overpotential. Cl⁻ ions preferably adhered to {100} facets to modulate growth rates of these facets is proved. The discovered growth modes to prepare Cu₂O microarchitectures composed of multiple building units inaccessible with existing methods are employed. Polyvinyl alcohol (PVA) additives can guarantee all pre-electrodeposits simultaneously evolve into uniform microarchitectures, instead of forming undesired microstructures on bare electrode surfaces in following electrodeposition processes is discovered. The designed Cu₂O microarchitectures can be converted into noble metal microstructures with shapes unchanged, which can be used as surface-enhanced Raman scattering substrates. An electrochemical avenue toward rational design of complex inorganic microarchitectures is opened up.

Nature Communications, Published online: 29 February 2024; doi:10.1038/s41467-024-46209-8

Nature Reviews Methods Primers, Published online: 29 February 2024; doi:10.1038/s43586-024-00293-8

Inspired by voltage-gated ion channels in neurons, a two-dimensional nanofluidic ionic transistor was fabricated, which operates based on the response to transmembrane potential. The device demonstrates a high on/off ratio of ~2000 and can transition from ambipolar to unipolar behavior with a low subthreshold swing of 560 mV/decade. The successful implementation of ionic logic gate circuits, including “NOT”, “NAND”, and “NOR” gates, paves a promising pathway towards ion-based brain-like computing.

Abstract

Voltage-gated ion channels prevalent in neurons play important roles in generating action potential and information transmission by responding to transmembrane potential. Fabricating bio-inspired ionic transistors with ions as charge carriers will be crucial for realizing neuro-inspired devices and brain-liking computing. Here, we reported a two-dimensional nanofluidic ionic transistor based on a MXene membrane with sub-1 nm interlayer channels. By applying a gating voltage on the MXene nanofluidic, a transmembrane potential will be generated to active the ionic transistor, which is similar to the transmembrane potential of neuron cells and can be effectively regulated by changing membrane parameters, e.g., thickness, composition, and interlayer spacing. For the symmetric MXene nanofluidic, a high on/off ratio of ~2000 can be achieved by forming an ionic depletion or accumulation zone, contingent on the sign of the gating potential. An asymmetric PET/MXene-composited nanofluidic transitioned the ionic transistor from ambipolar to unipolar, resulting in a more sensitive gate voltage characteristic with a low subthreshold swing of 560 mV/decade. Furthermore, ionic logic gate circuits, including the “NOT”, “NAND”, and “NOR” gate, were implemented for neuromorphic signal processing successfully, which provides a promising pathway towards highly parallel, low energy consumption, and ion-based brain-like computing.

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

Ionic liquids and their various analogues are without doubt the scientific sensation of recent decades, paving the yellow brick road to a worldly version of Oz's green “Emerald city”—a more sustainable society. Their versatile properties, originating from an almost inconceivably large number of possible cation and anion combinations, allows tuning of structures to serve a desired purpose.

Abstract

Ionic liquids and their various analogues are without doubt the scientific sensation of the last few decades, paving the way to a more sustainable society. Their versatile suite of properties, originating from an almost inconceivably large number of possible cation and anion combinations, allows tuning of the structure to serve a desired purpose. Ionic liquids hence offer a myriad of useful applications from solvents to catalysts, through to lubricants, gas absorbers, and azeotrope breakers. The purpose of this review is to explore the more unexpected of these applications, particularly in the energy space. It guides the reader through the application of ionic liquids and their analogues as i) phase change materials for thermal energy storage, ii) organic ionic plastic crystals, which have been studied as battery electrolytes and in gas separation, iii) key components in the nitrogen reduction reaction for sustainable ammonia generation, iv) as electrolytes in aluminum-ion batteries, and v) in other emerging technologies. It is concluded that there is tremendous scope for further optimizing and tuning of the ionic liquid in its task, subject to sustainability imperatives in line with current global priorities, assisted by artificial intelligence.

Recent progress of Raman spectroscopy using deep-ultraviolet light and circularly polarized light and first-principles calculation for single and double resonance Raman spectra.

Abstract

Recent progress of Raman spectroscopy on carbon nanotubes and 2D materials is reviewed as a topical review. The Raman tensor with complex values is related to the chiral 1D/2D materials without mirror symmetry for the mirror in the propagating direction of light, such as chiral carbon nanotube and black phosphorus. The phenomenon of complex Raman tensor is observed by the asymmetric polar plot of helicity-dependent Raman spectroscopy using incident circularly-polarized lights. First-principles calculations of resonant Raman spectra directly give the complex Raman tensor that explains helicity-dependent Raman spectra and laser-energy-dependent relative intensities of Raman spectra. In deep-ultraviolet (DUV) Raman spectroscopy with 266 nm laser, since the energy of the photon is large compared with the energy gap, the first-order and double resonant Raman processes occur in general k points in the Brillouin zone. First-principles calculation is necessary to understand the DUV Raman spectra and the origin of double-resonance Raman spectra. Asymmetric line shapes appear for the G band of graphene for 266 nm laser and in-plane Raman mode of WS₂ for 532 nm laser, while these spectra show symmetric line shapes for other laser excitation. The interference effect on the asymmetric line shape is discussed by fitting the spectra to the Breit–Wigner–Fano line shapes.

Nature, Published online: 28 February 2024; doi:10.1038/s41586-024-07078-9

A universal vapor-phase synthesis method is developed to realize the growth of various halide perovskites (e.g., MAPbBr₃, FAPbBr₃, MAPbI₃, FAPbI₃, and Cs₄PbI₆) with lateral size up to 1.5 cm × 1.5 cm and long-term stability over 180 days under air-environment. The resultant perovskite photodetectors exhibit attractive optoelectronic properties such as superior responsivity, ultrafast response time, and outstanding photoelectric image sensing capability.

Abstract

Ultrathin halide perovskites have drawn tremendous attention in nano-/micro-optoelectronic devices due to their fascinating performance and capability for chip integration. Unfortunately, it is highly challenging to obtain large-scale and chronically stable ultrathin halide perovskites for practical application. Herein, the universal low-temperature vapor-phase synthesis of ultrathin perovskite family materials with thickness down to 2D level and lateral size up to 1.5 cm × 1.5 cm is reported by developing a self-limiting chemical vapor deposition strategy. The perovskite products are found to exhibit superior stability over 180 days under an air environment. The resultant photodetectors demonstrate charming optoelectronic properties such as superior responsivity (3.7 × 10³ A W⁻¹), ultrafast response time (<10 µs), and outstanding low-level light image sensing capability. This universal perovskite synthesis strategy offers great potential for practical applications of halide perovskites in future nano-/micro-optoelectronic devices.

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

A dual-logic-in-memory device is demonstrated through a single bidirectional polarization-integrated 2D ferroelectric field-effect transistor.

A dual-logic-in-memory device is demonstrated through a single bidirectional polarization-integrated 2D ferroelectric field-effect transistor.

Light: Science & Applications, Published online: 27 February 2024; doi:10.1038/s41377-024-01406-4

A GdNiO₃-based interfacial memristor is proposed, which possesses ultra-high stability performance. Combined with the comprehensive microstructure results, this behavior is ascribed to the interface Schottky barrier variation caused by the 1D oxygen vacancy channel conduction according to the transmission electron microscopy results. Highly accurate neural firing pattern recognition up to ≈99.75% accuracy and monitoring of pattern transitions are succeeded in achieving.

Abstract

Perovskite-type rare earth nickelates based memristor have recently attracted extensive attention in the field of novel storage computing due to their special electronic structure and exotic physical properties. However, there is still a shortage of memristors with ultra-high stability performance, which will provide a solid foundation for future neural network computing with high accuracy recognition rates. Here, a GdNiO₃-based interfacial memristor is presented, which possesses ultra-high stable performance, such as electroforming-free, low device-to-device variation, reliable cyclic switching, high on/off ratio (≈10⁴) and stable pulse modulation of conduction. Combined with the comprehensive microstructure results, this behavior is ascribed to the interface Schottky barrier variation caused by the 1D oxygen vacancy channel conduction according to the transmission electron microscopy results. In particular, based on the device's stable pulse modulation plasticity performance, the study also succeeds in achieving highly accurate neural firing pattern recognition up to ≈99.75% accuracy and monitoring of pattern transitions by implementing a reservoir computing system based on the device. This research advances the progress of nickelates in novel storage computing and paves the way for future efficient memristor-based reservoir computing systems to handle more complex temporal tasks.

Nature Communications, Published online: 27 February 2024; doi:10.1038/s41467-024-46066-5

Enhancing interfacial adhesion in flexible devices is crucial for their stretchability and longevity. This study employs gold-chalcogen bonding and mercapto silane bridges to reduce sliding and wrinkling issues. The improved fabrication workflow addresses soft lithography challenges to enhance the reliability of flexible microelectronics, making them more practical for applications in biomedical, environmental, and consumer electronics.

Abstract

Van der Waals semiconductors (vdWS) offer superior mechanical and electrical properties and are promising for flexible microelectronics when combined with polymer substrates. However, the self-passivated vdWS surfaces and their weak adhesion to polymers tend to cause interfacial sliding and wrinkling, and thus, are still challenging the reliability of vdWS-based flexible devices. Here, an effective covalent vdWS–polymer lamination method with high stretch tolerance and excellent electronic performance is reported. Using molybdenum disulfide (MoS₂)and polydimethylsiloxane (PDMS) as a case study, gold–chalcogen bonding and mercapto silane bridges are leveraged. The resulting composite structures exhibit more uniform and stronger interfacial adhesion. This enhanced coupling also enables the observation of a theoretically predicted tension-induced band structure transition in MoS₂. Moreover, no obvious degradation in the devices’ structural and electrical properties is identified after numerous mechanical cycle tests. This high-quality lamination enhances the reliability of vdWS-based flexible microelectronics, accelerating their practical applications in biomedical research and consumer electronics.

Light: Science & Applications, Published online: 26 February 2024; doi:10.1038/s41377-024-01405-5