Jing Zhang

Nature Communications, Published online: 20 April 2023; doi:10.1038/s41467-023-38012-8

Metal free’ materials offer a cheap and chemical benign platform for magnetism, however, the typical source of magnetism are unpaired electrons of a metal, thus designing ‘metal free’ magnetic materials represents a significant challenge. Here, Du et al present a strategy for enhancing the magnetism in carbon nitride using boron bridges.

Nature Photonics, Published online: 20 April 2023; doi:10.1038/s41566-023-01197-x

Ultrathin 10.2-nm-thick (~λ/30,000) Ti3C2Tx MXene assemblies that offer an absorption of 49.2%, which is close to the theoretical limit of 50%, in the range of 0.5–10 THz are reported, benefiting terahertz optoelectronic and photothermoelectric devices.

Nature Photonics, Published online: 20 April 2023; doi:10.1038/s41566-023-01195-z

A passively mode-locked quantum cascade laser (QCL) is developed by employing a heterogeneous gain medium and integrating graphene saturable absorbers along the entire QCL waveguide. Self-starting optical pulses of 4.0 ps are electrically generated in the 2.30–3.55 THz frequency range.

Nature Communications, Published online: 21 April 2023; doi:10.1038/s41467-023-37973-0

Sensing and processing UV light is essential for advanced artificial visual perception system. Here, the authors report a controllable UV-ultrasensitive neuromorphic vision sensor using organic phototransistors to integrate sensing, memory and processing functions, and perform the static image and dynamic movie recognition.

Nature Communications, Published online: 21 April 2023; doi:10.1038/s41467-023-38024-4

The microscopic mechanism of the metal-insulator transition in 2D disordered semiconductors is not fully understood. Shin et al. propose a universal mechanism due to curvature-induced band gap fluctuations in a structurally disordered system, based on gate-tunable scanning tunneling microscopy on monolayer MoS2.

Nature Physics, Published online: 20 April 2023; doi:10.1038/s41567-023-02017-3

The spontaneous topological Hall effect, combining non-coplanar antiferromagnetic order with finite scalar spin chirality in the absence of a magnetic field, is now experimentally demonstrated for the triangular lattice compounds CoTa3S6 and CoNb3S6.

Nature Physics, Published online: 20 April 2023; doi:10.1038/s41567-023-02023-5

So far, a continuous time crystal has only been implemented on a quantum system. Optically driven many-body interactions in a nanomechanical photonic metamaterial now allow the realization of a classical continuous time crystal.

Nature Physics, Published online: 20 April 2023; doi:10.1038/s41567-023-02043-1

Time crystals are a new state of matter. Conventional crystal properties are periodic in space, while the properties of a time crystal are periodic in time. A continuous quantum time crystal has recently been realized, and now, using optically driven many-body interactions in a nano-mechanical photonic metamaterial, a classical continuous time crystal has been created.

The earthworm is widely distributed, with 4000 species in the world and more than 300 species in China (1, 2), where they are in demand as fishing bait, livestock feed, and components of traditional medicine (3). In recent years, poachers in China have started using soil electrocution to capture earthworms, putting earthworm populations and ecosystems at risk. In February, China prohibited the practice. The decision is a necessary first step to protect agriculture, but to ensure that electric capture ceases, China must follow up with legislation to support the implementation of the ban.

The preform-to-fiber thermal drawing of magnetically responsive soft composite materials enables the fabrication of magnetic fibers with extreme aspect ratios and intricate internal multimaterial structures, resulting in diverse functionalities. The soft magnetic fibers can optimally steer in many different directions, lift heavy loads, and also can be weaved into forming functional magnetic textiles for programmable shape-morphing.

Abstract

Magnetically responsive soft materials are promising building blocks for the next generation of soft robotics, prosthesis, surgical tools, and smart textiles. To date, however, the fabrication of highly integrated magnetic fibers with extreme aspect ratios, that can be used as steerable catheters, endoscopes, or within functional textiles remains challenging. Here, multimaterial thermal drawing is proposed as a material and processing platform to realize 10s of meters long soft, ultrastretchable, yet highly resilient magnetic fibers. Fibers with a diameter as low as 300 µm and an aspect ratio of 10⁵ are demonstrated, integrating nanocomposite domains with ferromagnetic microparticles embedded in a soft elastomeric matrix. With the proper choice of filler content that must strike the right balance between magnetization density and mechanical stiffness, fibers withstanding strains of >1000% are shown, which can be magnetically actuated and lift up to 370 times their own weight. Magnetic fibers can also integrate other functionalities like microfluidic channels, and be weaved into conventional textiles. It is shown that the novel magnetic textiles can be washed and sustain extreme mechanical constraints, as well as be folded into arbitrary shapes when magnetically actuated, paving the way toward novel intriguing opportunities in medical textiles and soft magnetic systems.

The discovery of high-temperature antiferromagnetism in NiSi with T _N ⩾ 700 K is reported. The antiferromagnetism is accompanied by a small uncompensated ferromagnetic component, which can be independently tuned by a small magnetic field, resulting in a one-step magnetic switching transition. Thus, a new venue for spintronics research is envisaged in this technologically important material.

Abstract

Envisaging antiferromagnetic spintronics pivots on two key criteria of high transition temperature and tuning of underlying magnetic order using straightforward application of magnetic field or electric current. Here, it is shown that NiSi metal can provide suitable new platform in this quest. First, the study unveils high-temperature antiferromagnetism in single-crystal NiSi with Néel temperature, T _N ⩾ 700 K. Antiferromagnetic order in NiSi is accompanied by non-centrosymmetric magnetic character with small ferromagnetic component in the a–c plane. Second, it is found that NiSi manifests distinct magnetic and electronic hysteresis responses to field applications due to the disparity in two moment directions. While magnetic hysteresis is characterized by one-step switching between ferromagnetic states of uncompensated moment, electronic behavior is ascribed to metamagnetic switching phenomena between non-collinear spin configurations. Importantly, the switching behaviors persist to high temperature. The properties underscore the importance of NiSi in the pursuit of antiferromagnetic spintronics.

Controllable switching between Schottky and p–n junction is constructed in a single MoS₂ flake by ionic gating. The device exhibits rectification ratio as high as 10⁶ and excellent photoelectric performance. The electric field control of such high-performance Schottky and p–n junctions opens up fresh perspectives for studying the behavior of junctions and the development of 2D electronic devices.

Abstract

Semiconductor junctions are of great significance for the development of electronic and optoelectronic devices. Here, controllable switching is demonstrated from a Schottky junction to a p–n junction in a partially ionic liquid-gated MoS₂ device with two types of metal contacts. Excellent rectification behavior with a current on-off ratio exceeding 10⁶ is achieved in both Schottky and p–n junction modes. The formation of Schottky junction at the Pd electrode/MoS₂ contact and p–n junction at the p-MoS₂/n-MoS₂ interface is revealed by spatially resolved photocurrent mappings. The switching between the two junctions under ionic gate modulation is correlated with the evolution of the energy band, further validated by the finite element simulation. The device exhibits excellent photodetection properties in the p–n junction mode, including an open circuit voltage up to 0.84 V, a responsivity of 0.24 A W⁻¹, a specific detectivity of 1.7 × 10¹¹ Jones, a response time of hundreds of microseconds and a linear dynamic range of up to 91 dB. The electric field control of such high-performance Schottky and p–n junctions opens up fresh perspectives for studying the behavior of junction and the development of 2D electronic devices.

Mechanically driven reversible polarization switching is realized in ferroelectric BiFeO₃ thin films. The reversible mechanical switching arises from the interplay among the flexoelectric effect, the piezoelectric effect, and the internal upward built-in field in BiFeO₃ films. This study gains a deeper insight into the mechanism and control of mechanically driven ferroelectric switching, and provides guidance for exploring potential ferroelectric-based electro-mechanical microelectronics.

Abstract

Mechanically driven polarization switching via scanning probe microscopy provides a valuable voltage-free strategy for designing ferroelectric nanodomain structures. However, it is still challenging to realize reversible polarization switching with mechanical forces. Here, the mechanically driven reversible polarization switching observed in imprinted ferroelectric BiFeO₃ thin films is reported, i.e., up-to-down switching by a sharp scanning tip and down-to-up switching by a blunt tip. Free energy calculations, phase-field simulations, and piezoresponse force microscopy reveal that reversible mechanical switching arises from the interplay among the flexoelectric effect, the piezoelectric effect, and the internal upward built-in field in BiFeO₃ films. This study gains a deeper insight into the mechanism and control of mechanically driven polarization switching, and provides guidance for exploring potential ferroelectric-based electro-mechanical microelectronics.

A facile, controllable, and versatile method is reported to prepare monodisperse yolk-shell silica nanoparticles (NPs) by a novel selective etching strategy based on structural differences. This unprecedented and versatile synthesis strategy can be used to encapsulate essentially any silica-based, carbon-based, metal, or metal oxide NPs. Their applications in the fields of ultralow-dielectric constant materials, drug delivery systems, and catalysts are detailly explored.

Abstract

Herein, a facile, controllable, and versatile method is reported to prepare monodisperse yolk-shell and yolk-multishell silica nanoparticles (NPs) with mesoporous shells by a novel selective etching strategy. The mechanism of selective etching based on fluoride-silica chemistry is investigated in detail and thus provides a fundamentally novel principle for the fabrication of yolk-shell NPs. Specifically, this unprecedented and versatile synthesis strategy can be used to encapsulate essentially any silica-based, carbon-based, metal, metal oxide, or other possible NPs. Noteworthy is that most of the yolk-shell mesoporous silica (mSiO₂) NPs are prepared for the first time. To demonstrate the major structural and compositional advantages of the designed yolk-shell NPs, their applications in the fields of ultralow-dielectric constant (k) materials, drug delivery systems, and catalysts were explored. In detail, the lowest k value of the prepared yolk-shellordered mesoporous silica@mSiO₂/fluorinated polybenzoxazole composite films is 2.02; The obtained yolk-shell mSiO₂/C@mSiO₂/C NPs possess high hydrophilicity and pH-responsive sensitivity; The conversion of the catalytic reaction of the designed magnetic yolk-shell hollow Fe₃O₄@SiO₂/Au@mSiO₂ NPs at 20 min is 97% with a high conversion rate (92%) and recyclability even after 10 reuses. This innovative work lays a solid foundation for freely tailorable yolk-shell encapsulation and will greatly stimulate more efforts devoted to relevant research and development.

The uniaxial anisotropic interlayer Dzyaloshinskii–Moriya interaction (IL-DMI) constants are determined quantitatively in synthetic ferromagnetic/antiferromagnetic Pt/Co/Pt/Ru/Pt/Co/Ta structures. The first-principles calculations elucidate that the in-plane symmetry breaking along two high symmetric directions induces the anisotropic IL-DMI. The results show that the IL-DMI can be tuned by the Ru-layer-thickness and beneficial to potential applications in 3D magnetic structures driven by spin–orbit torques.

Abstract

The interfacial Dzyaloshinskii–Moriya interaction (DMI) in ferromagnetic/non-magnetic-metal bilayers is essential to stabilize chiral spin textures for potential applications. Recent works reveal that the interlayer DMI is beneficial to designing 3D chiral spin textures that possess fundamental importance and the associated technological promises. Here, the interlayer DM constants are determined quantitatively in synthetic ferromagnetic/antiferromagnetic Pt/Co/Pt/Ru/Pt/Co/Ta structures. The results demonstrate that the interlayer DMI shows uniaxial anisotropic characteristics. The first-principles calculations elucidate that the anisotropic interlayer DMI is induced by the in-plane symmetry breaking along two high symmetric directions, which favors the magnetization of adjacent ferromagnetic layers canting in different directions. The anisotropic interlayer DMI is also confirmed by spin-orbit torque driven asymmetric magnetization switching. Moreover, the interlayer DMI can be tuned by the Ru-layer-thickness and beneficial to designing 3D spin textures for future spintronic devices.

The PEDOT:PSS film can be oxidized and reduced by different redox agents, causing the “CHINA” pattern appear different colors in infrared, which originates from the mobile polaronic transport property of PEDOT chains. The emission spectra of PEDOT:PSS presents reversible property during the recycle redox agents post-treatment, indicating that PEDOT:PSS is a smart infrared rewritable material.

Abstract

Thermal radiation spectrum regulation plays an important role in energy and information fields. Effectively hiding targets and rendering it invisible to infrared imaging detectors are great challenges in past decades. Herein, a smart infrared rewritable and emissivity tunable polymer film is proposed based on PEDOT:PSS. The adjustment ability for the thermal emission is attributed to the mobile polaronic of PEDOT that can be effectively regulated by redox agents, resulting in an infrared emission modulation > 30%. The conformation and molecular stacking order of PEDOT also present reversible property, accompanied with the transformation between dication state and neutral state. Finally, a technique for direct writing and erasing process in the infrared region is implemented, based on the simple redox treating process. This work aims to provide a simple strategy on fabricating rewritable films based on conducting polymer PEDOT:PSS, which can be potentially applied in infrared optics security printing.

A vertical GaN nanodiode with a 50 nm air channel is reported, fabricated using IC-compatible technologies, with a record field emission current of 11 mA@10 V. Notably, the device displays outstanding stability and fast switching characteristics with a sub-10 ns response time. Additionally, the temperature-dependent performance can guide the design of GaN NACTs for applications in extreme conditions.

Abstract

Nanoscale air channel transistors (NACTs) have received significant attention due to their remarkable high-frequency performance and high switching speed, which is enabled by the ballistic transport of electrons in sub-100 nm air channels. Despite these advantages, NACTs are still limited by low currents and instability compared to solid-state devices. GaN, with its low electron affinity, strong thermal and chemical stability, and high breakdown electric field, presents an appealing candidate as a field emission material. Here, a vertical GaN nanoscale air channel diode (NACD) with a 50 nm air channel is reported, fabricated by low-cost IC-compatible manufacturing technologies on a 2-inch sapphire wafer. The device boasts a record field emission current of 11 mA at 10 V in the air and exhibits outstanding stability during cyclic, long-term, and pulsed voltage testing. Additionally, it displays fast switching characteristics and good repeatability with a response time of fewer than 10 ns. Moreover, the temperature-dependent performance of the device can guide the design of GaN NACTs for applications in extreme conditions. The research holds great promise for large current NACTs and will speed up their practical implementation.

A unique strain-mediated lattice rotation strategy is introduced via nanocompositing to upsurge the optimized limits in the composition-to-structural pathway on rationally engineering the efficient thermoelectric material. The obtained ultra-high ZT_max (=1.13 at T = 773 K) successfully demonstrates the effectiveness of doping-induced structural variation and lattice rotation strategy, unlocking new prospects to develop atomistic lattice engineering in thermoelectric materials.

Abstract

A unique strain-mediated lattice rotation strategy is introduced via nanocompositing to upsurge the optimized limits in the composition-to-structural pathway on rationally engineering the efficient thermoelectric material. In this study, a special lattice rotation via strain engineering is realized to optimize the desired electronic and chemical environment for enhancing thermoelectric properties in n-type Bi₂S₂Se. This approach results in a unique transport phenomenon to assist high-energy electrons in transferring through the optimized transport channels, and appropriate structure disparity to significantly localize phonons. As a result, Sb over Cl doping in Bi₂S₂Se gently reduces E _g and introduces defect states in bandgap with shifting down the Fermi level, thus causing increase in carrier concentration, which contributes to a higher power factor of ≈7.18 µW cm⁻¹ K⁻² (at T = 773 K). Besides, a lower thermal conductivity of ≈0.49 W m⁻¹ K⁻¹ is driven through lattice strain and defect engineering. Consequently, an ultra-high ZT _max = 1.13 (at T = 773 K) and a high ZT _ave = 0.54 (323 K-773 K) are realized. This study not only leads to an extraordinary thermoelectric performance but also reveals a unique paradigm for electron transportation and phonon localization via lattice strain engineering.

Nature Communications, Published online: 19 April 2023; doi:10.1038/s41467-023-37927-6

Two-dimensional charge density waves in layered semiconductors may exhibit chirality. Here, the authors utilize thermal annealing to reversibly switch the in-plane chirality of charge density waves in 1T-TaS2 and demonstrate a vertical chirality-locking effect between the van der Waals-stacked layers.

Moiré bands separated by the primary and secondary gaps emerge in the superlattices of monolayer (MLG) and bilayer graphene (BLG) aligned with the hexagonal boron nitride (BN). We study the tuning of the electronic and transport properties of such moiré superlattices through the periodic electrostatic potentials produced by the one-dimensional (1D) or two-dimensional (2D) patterned gating structure in the devices. The electrostatic potentials in graphene are produced by the spatially varying particle and hole doping due to the local quantum capacitance effect and can be modulated by the voltage () of the top patterned gating structure and that () of the uniform bottom gate. For the 1D devices of MLG/BN and BLG/BN, different sets of Fabry–Pérot interference like resistance patterns as a function of and can be observed when the Fermi level is shifted from the charge neutrality point (CNP) to the secondary gaps in MLG/BN and BLG/BN, and the overlapping regions of the patterns exhibit the highest resistance. The electronic states in these various regions of the resistance map show different moiré-band hybridization and spatial distribution. The secondary resistance patterns around the secondary gaps move away from the primary one with increasing twist angle (θ) between graphene and BN and their detailed patterns also depend on the orientation of the 1D potential with respect to that of the superlattice. The 2D periodic potentials can further split the subbands between CNP and the secondary gaps, depending on the commensurability of the moiré superlattice and the 2D potentials, and additional resistance peaks appear as a function of the gate voltages. The calculated resistance map for BLG/BN at is roughly consistent with recent experimental observations.

Control on spatial location and density of defects in two-dimensional materials can be achieved using electron beam irradiation. Conversely, ultralow accelerating voltages (5 kV) are used to measure surface morphology, with no expected defect creation. We find clear signatures of defect creation in monolayer MoS2 at these voltages. Evolution of and Raman modes with electron dose, and appearance of defect activated peaks indicate defect formation. To simulate Raman spectra of MoS2 at realistic defect distributions, while retaining density-functional theory accuracy, we combine machine-learning force fields for phonons and eigenmode projection approach for Raman tensors. Simulated spectra agree with experiments, with sulphur vacancies as suggested defects. We decouple defects, doping and carbonaceous contamination using control (hBN covered and encapsulated MoS2) samples. We observe cryogenic photoluminescence quenching and defect peaks, and find that carbonaceous contamination does not affect defect creation. These studies have applications in photonics and quantum emitters.

Nature, Published online: 19 April 2023; doi:10.1038/s41586-023-05849-4

We demonstrate the memory effects and stimuli-regulated transport of molecules through an intelligent, phase-changing MoS2 membrane in response to external pH, a phenomenon unique to the 1T′ phase of MoS2.

Néel-type AFM order of the VPS₃ can break both spatial-inversion and time-reversal symmetries, which is verified by the magnetic-order-dependent second-harmonic generation (SHG). Accordingly, The SHG intensity shows a close correlation with the Néel-type magnetic order under varying temperatures, and an out-of-plane spin orientation can be further determined based on the specific six-fold symmetry.

Abstract

2D van der Waals (vdW) antiferromagnets have received intensive attention due to their terahertz resonance, multilevel magnetic-order states, and ultrafast spin dynamics. However, accurately identifying their magnetic configuration still remains a challenge owing to the lack of net magnetization and insensitivity to external fields. In this work, the Néel-type antiferromagnetic (AFM) order in 2D antiferromagnet VPS₃ with the out-of-plane anisotropy, which is demonstrated by the temperature-dependent spin–phonon coupling and second-harmonic generation (SHG), is experimentally probed. This long-range AFM order even persists at the ultrathin limit. Furthermore, strong interlayer exciton–magnon coupling (EMC) upon the Néel-type AFM order is detected based on the monolayer WSe₂/VPS₃ heterostructure, which induces an enhanced excitonic state and further certifies the Néel-type AFM order of VPS₃. The discovery provides optical routes as the novel platform to study 2D antiferromagnets and promotes their potential applications in magneto-optics and opto-spintronic devices.

Here, composition-graded Hf_{1- x} Zr _x O₂ ferroelectric thin films possessing more than two times faster polarization switching speed and better endurance characteristics than the conventional composition-uniform one are demonstrated. The transition of polarization switching dynamics from the nucleation-limited-switching mechanism to the domain-wall growth mechanism is responsible for these enhanced properties in the composition-graded Hf_{1- x} Zr _x O₂ thin films.

Abstract

The next-generation semiconductor memories are essentially required for the advancements in modern electronic devices. Ferroelectric memories by HfO₂-based ferroelectric thin films (FE-HfO₂) have opened promising directions in recent years. Nevertheless, improving the polarization switching speed of FE-HfO₂ remains a critical task. In this study, it is demonstrated that the composition-graded Hf_{1- x} Zr _x O₂ (HZO) ferroelectric thin film has more than two times faster polarization switching speed than the conventional composition-uniform one. Meanwhile, it has excellent ferroelectricity and improved endurance characteristics. It is also discovered that when the HZO thin film has a gradient composition, the polarization-switching dynamics shifts from the nucleation-limited-switching mechanism to the domain-wall growth mechanism. Moreover, the transition of switching dynamics is responsible for the faster speed and better endurance of the composition-graded HZO thin film. These findings not only reveal the physical mechanisms of this material system but also provide a new strategy for memory devices having faster speed and higher endurance.