Jiuxiang Dai

Robust spin-orbit-torque (SOT) driven perpendicular magnetization switching in the van der Waals Fe₃GaTe₂ at room temperature is achieved with a relatively low critical current density of 1.3 × 10⁷ A cm⁻². These results offer new opportunities to breakthrough the downscaled problem of SOT-magnetic random-access memory based on 3D ferromagnets.

Abstract

The emerging wide varieties of the van der Waals (vdW) magnets with atomically thin and smooth interfaces hold great promise for next-generation spintronic devices. However, due to the lower Curie temperature of the vdW ferromagnets than room temperature, electrically manipulating its magnetization at room temperature has not been realized. In this work, it is demonstrated that the perpendicular magnetization of the vdW ferromagnet Fe₃GaTe₂ can be effectively switched at room temperature in the Fe₃GaTe₂/Pt bilayer by spin–orbit torques (SOTs) with a relatively low current density of 1.3 × 10⁷A cm⁻². Moreover, the high SOT efficiency of ξ_DL ≈ 0.28 is quantitatively determined by harmonic measurements, which is higher than those in Pt-based heavy metal/conventional ferromagnet devices. The findings of room-temperature vdW ferromagnet switching by SOTs provide a significant basis for the development of vdW-ferromagnet-based spintronic applications.

Trench-bridged GaN/Ga₂O₃/GaN device is fabricated. According to the manipulation of the ionization and de-ionization processe of oxygen vacancies within the Ga₂O₃, the device shows fast photoresponse at low voltages and persistent photoconductivity behavior at high voltages. Accordingly, various functions of the photodetector and neuromorphic vision sensor are achieved by one device and switched via bias voltage regulation.

Abstract

Simultaneous implementation of photodetector and neuromorphic vision sensor (NVS) on a single device faces a great challenge, due to the inherent speed discrepancy in their photoresponse characteristics. In this work, a trench-bridged GaN/Ga₂O₃/GaN back-to-back double heterojunction array device is fabricated to enable the advanced functionalities of both devices on a single device. Interestingly, the device shows fast photoresponse and persistent photoconductivity behavior at low and high voltages, respectively, through the modulation of oxygen vacancy ionization and de-ionization processes in Ga₂O₃. Consequently, the role of the optoelectronic device can be altered between the photodetector and NVS by simply adjusting the magnitude of bias voltage. As a photodetector, the device is able to realize fast optical imaging and optical communication functions. On the other hand, the device exhibits outstanding image sensing, image memory, and neuromorphic visual pre-processing as an NVS. The utilization of NVS for image pre-processing leads to a noticeable enhancement in both recognition accuracy and efficiency. The results presented in this work not only offer a new avenue to obtain complex functionality on a single optoelectronic device but also provide opportunities to implement advanced robotic vision systems and neuromorphic computing.

Electrospinning-derived aligned IGZO (a-IGZO) NFN FETs are achieved. The superior electrical performance of the transistors is comparable to devices of the same type fabricated in high-temperature processes. The successful assembly of multi-scenario devices based on a-IGZO FETs also confirms thepotential of electrospun highly oriented inorganic fiber arrays obtained in low-temperature processes forapplications in nano-integrated circuits andvarious functional devices.

Abstract

Metal oxide field-effect transistors (MOFETs) represent a promising technology for applications in existing but alsoemerging large-area electronics. Simultaneously, the rise of 1D nanomaterials with unique properties, represented by nanofibers (NFs), has also energized research. Thus, developing 1D nanofiber networks (NFNs) to act as the potential building blocks for use in fundamental elements of transistors is considered to be a promising approach torealize high-performance 1D electronics. However, high processing temperatures and disordered nanofiber distribution represent two remaining technical challenges. Here, electrospun highly aligned IGZO (a-IGZO) nanofiber arrays with low-thermal-budget of 350 °C and impressive device characteristics are achieved, including a μFE of 5.63 cm2 V^–1 s^–1 and superior on/off current ratio of ≈107. When ALD-derived high-k HfAlOx thin films are employed as gate dielectrics, the source/drain voltage (VDS) can be substantially reduced by ten times to a range of only 03 V, along with a three times improvement in mobility to a respectable value of 15.9 cm2 V^–1 s^–1. Successful integrations of logic operation, sensor, and flexible devices implies the potential prospect of a-IGZO NFN FETs in multifunctional electronics. The strategy for combining cryogenic processes and parallel arrays provides a feasible and reliable route in building future low-power, high-performance flexible electronics.

Liquid metals spontaneously form protective oxide skins on their surfaces when exposed to oxygen. While the oxide layer is generally considered a nuisance, this article reports a mechanism that harnesses the electrochemical energy of the spontaneous re-growth of liquid metal oxide after being damaged by mechanical disturbances. This discovery enables the design of strain-activated stretchable batteries and self-powered soft devices.

Abstract

Liquid metals, such as Gallium-based alloys, have unique mechanical and electrical properties because they behave like liquid at room temperature. These properties make liquid metals favorable for soft electronics and stretchable conductors. In addition, these metals spontaneously form a thin oxide layer on their surface. Applications made possible by this delicate oxide skin include shape reconfigurable electronics, 3D-printed structures, and unconventional actuators. This paper introduces a new approach where liquid metal oxide serves as an electrochemical energy source. By mechanically rupturing their surface oxide, liquid metals form a galvanic cell and convert their chemical energy to electrical energy. When dispersing liquid metals into an ionically-conductive liquid to form emulsions, this composite material can provide ∼500 mV of open-circuit voltage and up to ∼4 μW of power. Protected by the naturally occurring oxide skin, the passivating oxide layer of the liquid metal shields it from self-discharge over time. The device is also stable in harsh environments, such as high temperature or aquatic conditions. Future applications of this device are demonstrated by designing a strain-activated stretchable battery and a pressure-sensitive self-powered keypad. These findings may unlock new pathways to design stretchable batteries and harness their inherent energy for self-powered robust devices.

Abstract

Two-dimensional (2D) semiconductors, especially transition metal dichalcogenides (TMDCs), have been proven to be excellent channel materials for the next-generation integrated circuit (IC). However, the contact problem between 2D TMDCs and metal electrodes has always been one of the main factors restricting their development. In this review, we summarized recent work on 2D TMDCs contact from the perspective of compatible integration with silicon processes and practical application requirements, including the contact performance evaluation indicators, special challenges encountered in 2D TMDCs, and recent optimization methods. Specifically, we sorted out and highlighted the performance indicators of 2D TMDCs contacts, including contact resistance (R_C), contact scaling, contact stability, and contact electrical/thermal conductivity. Special challenges of 2D TMDCs and metal contact, such as severe Fermi level pinning, large R_C and difficult doping, are systematically discussed. Furthermore, typical methods for optimizing 2D TMDCs R_C, edge contact strategies for scaling contact lengths, and solutions for improving contact stability are reviewed. Based on the current research and problems, the development direction of 2D TMDCs contacts that meet the silicon-based compatible process and application performance requirements is proposed.

The asymmetrical growth of a single-wall carbon nanotube from a sub-2-nm Pt catalyst is observed at atomic scale under reactive conditions. The axis-symmetry of the SWCNT is broken due to the formation of step edges around the tube-catalyst interface, which generates topological defects around the wall and results in variations of tube chirality.

Abstract

The asymmetrical growth of a single-wall carbon nanotube (SWCNT) by introducing a change of a local atomic structure, is usually inevitable and supposed to have a profound effect on the chirality control and property tailor. However, the breaking of the symmetry during SWCNT growth remains unexplored and its origins at the atomic-scale are elusive. Here, environmental transmission electron microscopy is used to capture the process of breaking the symmetry of a growing SWCNT from a sub-2-nm platinum catalyst nanoparticle in real-time, demonstrating that topological defects formed on the side of a SWCNT can serve as a buffer for stress release and inherently break its axis-symmetrical growth. Atomic-level details reveal the importance of the tube-catalyst interface and how the atom rearrangement of the solid-state platinum catalyst around the interface influences the final tubular structure. The active sites responsible for trapping carbon dimers and providing enough driving force for carbon incorporation and asymmetric growth are shown to be low-coordination step edges, as confirmed by theoretical simulations.

Pt atomic layers catalysts with electron-deficient Pt sites and epitaxial strain are successfully grown on low-cost CrN nanoparticles via a facile thermal ammonlysis method. The Pt atomic layers on CrN electrocatalyst deliver outstanding activity and durability for the formic acid oxidation reaction, guiding the development of low-cost Pt-based catalysts for various applications.

Abstract

The construction of platinum (Pt) atomic layers is an effective strategy to improve the utilization efficiency of Pt atoms in electrocatalysis, thus is important for reducing the capital costs of a wide range of energy storage and conversion devices. However, the substrates used to grow Pt atomic layers are largely limited to noble metals and their alloys, which is not conducive to reducing catalyst costs. Herein, low-cost chromium nitride (CrN) is utilized as a support for the loading of epitaxial ultrathin Pt atomic layers via a simple thermal ammonolysis method. Owing to the strong anchoring and electronic regulation of Pt atomic layers by CrN, the obtained Pt atomic layers catalyst (containing electron-deficient Pt sites) exhibits excellent activity and endurance for the formic acid oxidation reaction, with a mass activity of 5.17 A mg_Pt ⁻¹ that is 13.6 times higher than that of commercial Pt/C catalyst. This novel strategy demonstrates that CrN can replace noble metals as a low-cost substrate for constructing Pt atomic layers catalysts.

The recent progress of negative capacitance (NC) field effect transistors (FETs) with ferroelectric gate stack is summarized in this review, including the related concepts for in-depth understanding of NC FETs. Moreover, some high-performance NC FETs with different ferroelectric gate stacks are presented. Finally, influential factors and challenges for improving 2D NC FETs are proposed.

Abstract

Steep subthreshold swing (SS) is a decisive index for low energy consumption devices. However, the SS of conventional field effect transistors (FETs) has suffered from Boltzmann Tyranny, which limits the scaling of SS to sub-60 mV dec⁻¹ at room temperature. Ferroelectric gate stack with negative capacitance (NC) is proved to reduce the SS effectively by the amplification of the gate voltage. With the application of 2D ferroelectric materials, the NC FETs can be further improved in performance and downscaled to a smaller dimension as well. This review introduces some related concepts for in-depth understanding of NC FETs, including the NC, internal gate voltage, SS, negative drain-induced barrier lowering, negative differential resistance, single-domain state, and multi-domain state. Meanwhile, this work summarizes the recent advances of the 2D NC FETs. Moreover, the electrical characteristics of some high-performance NC FETs are expressed as well. The factors which affect the performance of the 2D NC FETs are also presented in this paper. Finally, this work gives a brief summary and outlook for the 2D NC FETs.

A 3.9 nm-thick CeO₂ single crystal with 120 µm lateral size is synthesized over sapphire substrate through salt-assisted chemical vapor deposition method. The photoresponsitivity reaches 43.6 A W⁻¹ while the detectivity reaches 7.58 × 10¹¹ Jones under the 395 nm laser irradiation. This work demonstrates the possibility of synthesis of large-size high-quality 2D rare-earth oxides and their strong potential in high-performance optoelectronic devices.

Abstract

Few rare-earth (RE) atoms incorporated in lattice greatly tunned the optical, electrical, magnetic, and catalytic performance of doped crystal through the peculiar atomic electron structure of RE. The dimensionality scale-down of RE oxides can further promote their unique traits and broaden their applications. The UV photodetection performance of (111) oriented CeO₂ thin film is limited by the existence of grain boundaries, defects, and strains. Consequently, single-crystal 2D CeO₂ is promising for photodetection as it lacks of grain boundaries and defects. However, the synthesis of large-sized high-quality 2D CeO₂ with lateral dimensions over 100 µm is challenging. In this work, a 3.9 nm thick CeO₂ single crystal with 120 µm lateral size is synthesized over a sapphire substrate through a salt-assisted chemical vapor deposition method, in which an intermediate insulating CeAlO₃ layer is formed between the substrate and 2D CeO₂ to enhance the crystal lattice matching and therefore facilitates the large area growth. The photodetector based on 2D CeO₂ exhibits a photo response from 395 to 532 nm, possibly ascribed to a micro-strain narrowed bandgap induced at the heterointerface. The photoresponsivity reaches 43.6 A W⁻¹ while the detectivity reaches 7.58 × 10¹¹ Jones under the 395 nm laser irradiation. Besides, the sub-ms switching kinetics is achieved without gating bias, which is significantly improved over other reported RE oxides-based photodetectors. This work demonstrates the possibility of the synthesis of large-size high-quality 2D RE oxides and their strong potential in high-performance optoelectronic devices.

Nature Communications, Published online: 30 October 2023; doi:10.1038/s41467-023-42710-8

Nature Nanotechnology, Published online: 30 October 2023; doi:10.1038/s41565-023-01526-9

Poorly crystalline impurities consisting of Na₂O, Na₂O₂, and NaOH were detected in Na₃OBr antiperovskite synthesised with commercially available Na₂O. These impurities form a eutectic mixture which melts at around 250 °C, reducing the activation energy for Na⁺ conduction from 0.47 eV to 0.43 eV.

Abstract

The sodium-rich antiperovskites (NaRAPs) with composition Na₃OB (B=Br, Cl, I, BH₄, etc.) are a family of materials that has recently attracted great interest for application as solid electrolytes in sodium metal batteries. Non-Arrhenius ionic conductivities have been reported for these materials, the origin of which is poorly understood. In this work, we combined temperature-resolved bulk and local characterisation methods to gain an insight into the origin of this unusual behaviour using Na₃OBr as a model system. We first excluded crystallographic disorder on the anion sites as the cause of the change in activation energy; then identified the presence of a poorly crystalline impurities, not detectable by XRD, and elucidated their effect on ionic conductivity. These findings improve understanding of the processing-structure-properties relationships pertaining to NaRAPs and highlight the need to determine these relationships in other materials systems, which will accelerate the development of high-performance solid electrolytes.

The MoS₂-based light-emitting diodes (LEDs) successfully demonstrate high luminescence and efficient carrier transports in an inverted p–i–n architecture. Scalable MoS₂ is grown by a two-step growth method and transferred onto the ZnO electron transport layer via an HF-assisted wet transfer. These electroluminescence devices exhibit superior optoelectrical properties compared to other transition metal dichalcogenide-based LEDs.

Abstract

Herein, a vertically inverted p–i–n architecture of light-emitting diodes (LEDs) is designed for manufacturing feasibility and demonstrated scalable bilayer MoS₂-based LEDs. A 4 inch scale bilayer MoS₂ is prepared by a two-step growth method allocating the pre-deposition of a few-nm thick metal film and post-sulfurization. To apply bilayer MoS₂ for an active layer in LEDs, the film is transferred over ZnO nanoparticle layers, an electron transfer layer, and then the rest of the LED components are constructed by thermal deposition. This vertically inverted LED architecture allows individual organic or inorganic components to incorporate without degradation during the wet-transfer process and transfer electron or hole carriers across separate layers, resulting in efficient radiative recombination in the MoS₂ emitting layer. MoS₂-based LEDs exhibit electroluminescence of ≈5.41 cd m⁻² throughout four active areas of 6.25 mm² at a driving voltage of 7 V. Therefore, this achievement can overcome the drawbacks of existing transition metal dichalcogenides (TMDs)-based optoelectrical applications and extend its potential in various fields, such as flexible, ultrathin, or transparent displays.

Artificial synapse combining short-term potentiation (STP) and long-term potentiation (LTP) in a single device is realized through the supramolecular engineering of 2D MoS₂. The Janus 2D material asymmetrically functionalized with a ferrocene (Fc)/ferrocenium (Fc⁺) redox couple and a photochromic azobenzene (Azo) responds to electrochemical and optical stimulus enabling fast-response STP as well as 4-bit (16 memory states) LTP.

Abstract

Artificial synapses combining multiple yet independent signal processing strategies in a single device are key enabler to achieve high-density of integration, energy efficiency, and fast data manipulation in brain-like computing. By taming functional complexity, the use of hybrids comprising multiple materials as active components in synaptic devices represents a powerful route to encode both short-term potentiation (STP) and long-term potentiation (LTP) in synaptic circuitries. To meet such a grand challenge, herein a novel Janus 2D material is developed by dressing asymmetrically the two surfaces of 2D molybdenum disulfide (MoS₂) with an electrochemically-switchable ferrocene (Fc)/ ferrocenium (Fc⁺) redox couple and an optically-responsive photochromic azobenzene (Azo). Upon varying the magnitude of the electrochemical stimulus, it is possible to steer the transition between STP and LTP, thereby either triggering electrochemical doping of Fc/Fc⁺ pair on MoS₂ or controlling an adsorption/desorption process of such redox species on MoS₂. In addition, a lower magnitude LTP is recorded by activating the photoisomerization of azobenzene chemisorbed molecules and therefore modulating the dipole-induced doping of the 2D semiconductor. Significantly, the interplay of electrochemical and optical stimuli makes it possible to construct artificial synapses where LTP can be boosted to 4-bit (16 memory states) while simultaneously functioning as STP.

Abstract

Transition metal dichalcogenides are attractive anode materials for sodium ion batteries (SIBs) due to their high theoretical capacity and large interlayer spacing. However, its practical application is hampered by the sluggish kinetics of Na⁺ insertion and structure collapse caused by Na⁺ insertion/deinsertion. Herein, the heterostructures of MoSe₂ nanosheets vertically growing on bowl-like carbon (MoSe₂@C) are designed and prepared by a template method coupled with selenization treatment to boost storage sodium performance. The hollow and collapse could provide enough storage space for Na⁺ and alleviate the volume expansion during the charge/discharge processes. MoSe₂ nanosheets vertically grown on carbon could expose more active sites for adsorbing Na⁺ to enhance the utilization rate of electrode materials. Moreover, building heterostructures by combining different phase components could facilitate Na⁺ diffusion and advance reaction kinetics. Benefiting from these merits, the bowllike MoSe₂@C shows outstanding reversible capacity (356.8 mAh·g⁻¹ after 1500 cycles at 1 A·g⁻¹) and remarkable rate performance (249.9 mAh·g⁻¹ 10 A·g⁻¹).

Publication date: November 2023

Source: Materials Today, Volume 70

Author(s): Kothuru Avinash, Fernando Patolsky

Nature Materials, Published online: 31 October 2023; doi:10.1038/s41563-023-01731-w

Bioinspired large-area atomically-thin graphene membranes exhibit distinct mechanical performances that provide an opportunity for modularization because the fiber-reinforced network composite structure is like a shell of “concrete” wrapping outside the graphene membrane. The nanoporous graphene membrane, after reinforcement, maintains a prominent separation performance of the breathable function with an ultrahigh gas permeance and an ultralow water vapor transportation rate.

Abstract

Nanoporous graphene membranes are attractive for molecular separations, but it remains challenging to maintain sufficient mechanical strength during scalable fabrication and module development. Inspired by the composite structure of cell membranes and cell walls, a large-area atomically thin nanoporous graphene membrane supported by a fiber-reinforced structure with strong interlamellar adhesion is designed. Compared with other graphene-based membranes of large scale, the fracture stress, fracture strength, and tensile stiffness of the composite membranes can be enhanced by a factor of 17, 67, and 94, respectively. This fiber-reinforced structure also confers stability of the composite membrane to different curvature states and repeated bending processes after 10 000 times, which provides an opportunity for modularization. The breathable function of such membrane with an ultrahigh gas permeance (≈8.6–23 L m⁻² d⁻¹ Pa⁻¹) and an ultralow water vapor transportation rate (WVTR) (≈23–129 g L m⁻² d⁻¹) is observed, superior to most commercial materials. This work provides a facile method to fabricate large-area graphene membranes and paves the road to practical application in the membrane separation field for other 2D films.

Superconducting Nb₂CT _x MXenes is realized through nitrogen doping in an atomic-exchange process. This is the first time to investigate MXene superconductivity at nanoscale based either on the single-flake or thin film. The anisotropic 2D superconductivity is successfully uncovered. Besides, processing the superconducting thin film over a 4 in. wafer opens up a space for scalable MXene-based superconducting devices.

Abstract

Superconductivty has recently been induced in MXenes through surface modification. However, the previous reports have mostly been based on powders or cold-pressed pellets, with no known reports on the intrinsic superconsucting properties of MXenes at the nanoale. Here, it is developed a high-temperature atomic exchange process in NH₃ atmosphere which induces superconductivity in either singleflakes or thin films of Nb₂CT _x MXene. The exchange process between nitrogen atoms and fluorine, carbon, and oxygen atoms in the MXene lattice and related structural adjustments are studied using both experiments and density functional theory. Using either single-flake or thin-film devices, an anisotropic magnetic response of the 2D superconducting transformation has been successfully revealed. The anisotropic superconductivity is further demonstrated using superconducting thin films uniformly deposited over a 4 in. wafers, which opens up the possibility of scalable MXene-based superconducting devices.