Jing Zhang

Nature Communications, Published online: 01 June 2022; doi:10.1038/s41467-022-30519-w

Neuromorphic computing requires the realization of high-density and reliable random-access memories. Here, Thean et al. demonstrate wafer-scale integration of solution-processed 2D MoS2 memristor arrays which show long endurance, long memory retention, low device variations, and high on/off ratio.

Graphene islands are subjected to different compressive strains from the opposite copper crystal plane after growing across the twin boundary. The monotonically changed graphene doping across different twin boundaries with unique spatial distribution is observed. This study is expected to have a potential impact on the growth of high-quality graphene on twinned copper substrates.

Abstract

Twin crystals, the formation energy of which is much smaller than that of ordinary grain boundaries, widely exist in the annealed copper and are hard to eliminate. The study of the effects of twin boundaries on graphene growth is of great significance to the understanding of graphene epitaxy. However, there are few studies on the effects of twin boundaries on the graphene growth process. Here, this article experimentally demonstrates that graphene islands are subjected to different compressive strains from the opposite copper crystal plane after growing across the twin boundary. Further results reveal that graphene can grow across different twin boundaries, such as atom steps, narrow valleys, and even micron-scale ridges, without forming linear defect. Therefore, strain-induced graphene doping can be manipulated with the type of twin boundaries and the location on the twin crystals. The transition region where the degree of doping changes monotonically across the twin boundary further confirms the different spatial doping phenomena of graphene islands. This work provides a new perspective for understanding the effect of twin boundaries on the graphene epitaxy, which is expected to have a potential impact on growing high-quality graphene on twinned copper substrates.

A facile approach is developed for constructing high-quality metal-2D semiconductor junctions through the edge-guided electrodeposition. Cross-sectional imaging and transport measurements confirm the seamless contact of Pd with each layer of MoS₂ greatly reduces the contact barrier to ≈20 meV and contact resistance to ≈290 Ω µm and thus significantly increases the performance of FETs with Pd nanowire edge contacts.

Abstract

2D semiconductors, such as MoS₂ have emerged as promising ultrathin channel materials for the further scaling of field-effect transistors (FETs). However, the contact barrier at the metal-2D semiconductor junctions still significantly limits the device's performance. By extending the application of electrochemical deposition in 2D electronics, a distinct approach is developed for constructing metal-2D semiconductor junctions in an edge-contacted configuration through the edge-guided electrodeposition of varied metals. Both high-resolution microscopic imaging and electrical transport measurements confirm the successful creation of high-quality Pd-2D MoS₂ junctions in desired geometry by combining electrodeposition with lithographic patterning. FETs are fabricated on the obtained Pd-2D MoS₂ junctions and it is confirmed that these junctions exhibit a reduced contact barrier of ≈20 meV and extremely low contact resistance of 290 Ω µm and thus increase the averaged mobility of MoS₂ FETs to ≈108 cm² V ⁻¹ s⁻¹. This approach paves a new way for the construction of metal-semiconductor junctions and also demonstrates the great potential of the electrochemical deposition technique in 2D electronics.

Nature Nanotechnology, Published online: 31 May 2022; doi:10.1038/s41565-022-01156-7

Author Correction: Monolayer mosaic heterostructures

Nature Communications, Published online: 30 May 2022; doi:10.1038/s41467-022-30516-z

Li intercalation of MoS2 induces a transition from the insulating H-phase to the metallic T-phase, with a sharp boundary in between. Here the authors stabilize the intermediate phase in twisted bilayer MoS2, by leveraging the Moiré potential which facilitates fast Li diffusion and uniform intercalation.

Nature Materials, Published online: 31 May 2022; doi:10.1038/s41563-022-01253-x

Twisted monolayer–multilayer graphene superlattices present bi-stable reconstruction states, with reversible switch in-between and long-distance propagation triggered by local mechanical perturbation. This provides additional degrees of freedom for moiré engineering.

Nature Electronics, Published online: 30 May 2022; doi:10.1038/s41928-022-00767-1

A solid-state electronic switch based on an atomic sheet of molybdenum disulfide is demonstrated in the 6G communication band with very high speed data transmission.

Nature Electronics, Published online: 30 May 2022; doi:10.1038/s41928-022-00766-2

Non-volatile analogue switches made from molybdenum disulfide can operate at frequencies of 480 GHz and achieve data transmission rates of 100 Gbit s–1, making them of potential use in sixth-generation communication technology.

A “shrinkage-assisted patterning by evaporation” (SHAPE) method is reported to fabricate freestanding and flexible electrodes. The multimaterial, multilayer, and shape-designable properties of the SHAPE method for fabrication of flexible electrodes provide electronics with unconfined stacking, customizable stretchability, and conformable integration on arbitrary surfaces, demonstrating their wide spectrum of applications in wearable and 3D integrated electronics.

Abstract

Flexible electrodes that are multilayer, multimaterial, and conformal are pivotal for multifunctional wearable electronics. Traditional electronic circuits manufacturing requires substrate-supported transfer printing, which limits their multilayer integrity and device conformability on arbitrary surfaces. Herein, a “shrinkage-assisted patterning by evaporation” (SHAPE) method is reported, by employing evaporation-induced interfacial strain mismatch, to fabricate auto-detachable, freestanding, and patternable electrodes. The SHAPE method utilizes vacuum-filtration of polyaniline/bacterial cellulose (PANI/BC) ink through a masked filtration membrane to print high-resolution, patterned, and multilayer electrodes. The strong interlayer hydrogen bonding ensures robust multilayer integrity, while the controllable evaporative shrinking property of PANI/BC induces mismatch between the strains of the electrode and filtration membrane at the interface and thus autodetachment of electrodes. Notably, a 500-layer substrateless micro-supercapacitor fabricated using the SHAPE method exhibits an energy density of 350 mWh cm⁻² at a power density of 40 mW cm⁻², 100 times higher than reported substrate-confined counterparts. Moreover, a digital circuit fabricated using the SHAPE method functions stably on a deformed glove, highlighting the broad wearable applications of the SHAPE method.

This work reports the programmable information encryption by 2D van der Waals rare-earth material ErOCl based on the editable electric-tunable photoluminescence (PL). The correct information encoded in PL outputs can be tactfully decrypted from the PL intensity ratio of two thermal coupling transitions (²H_11/2–⁴I_15/2 and ⁴S_3/2–⁴I_15/2), which has been applied to ASCII codes and images encryption with high-security.

Abstract

High-security encryption has always been important in economic and military fields as well as in daily life. 2D van der Waals (vdW) rare-earth (RE) materials have advantages in photoluminescence (PL) modulation to achieve high-security encryption because of their multiple sharp emission peaks, which will facilitate the multimode regulation for high-security encryption of programmable information. Here, programmable information encryption has been achieved by applying 2D vdW ErOCl via the editable electric-tunable PL. The correct information encoded in PL outputs can be tactfully decrypted from the PL intensity ratio of ²H_11/2–⁴I_15/2 and ⁴S_3/2–⁴I_15/2 transitions. This strategy for ASCII codes and images encryption with high-security is demonstrated. This novel approach, PL modulation of 2D vdW RE material based on programmable electric inputs, will mark a new path to achieve high-security encryption.

An electrically and optically switchable logic operation encryption based on the photoluminescence (PL) ratio of ZnTe is developed. Two PL emissions can be selectively regulated by the electric and optical fields due to different responses of band-edge emission and defect emission. This work provides a design for the creation of logic operation encryption and holds great promise for high-security encryption.

Abstract

Logic operation encryption is emerging as a novel cryptographic mode, protecting logic operation from being attacked and tampered, and is a modern extension of conventional encryption system. However, the existing encryption methods are not conducive to the logic operation encryption due to the complexity, signal mode, and non-adjustability of their design. Herein, an advanced logic operation encryption method is designed via the photoluminescence ratio of ZnTe, and the electrically and optically switchable NAND (Not AND) and NOR (Not OR) encryption based on this method is implemented. Two photoluminescence emissions can be selectively regulated by the gate voltage and excitation laser based on the different responses of band-edge emission and defect emission. This novel approach will shed light on the development of high-security encryption and computer information protection.

A novel broadband, strong electromagnetic intereference (EMI) shielding response fabric based on highly structured ferromagnetic graphene quartz fibers is demonstrated, which combines high conductivity and ferromagnetism to attain a synergistic effect for EMI shielding and electromagnetic wave (EMW) absorption, along with the specific woven superstructure of the fabric to introduce the additional multiple reflections and multichannel absorption of EMWs.

Abstract

Flexible electromagnetic interference (EMI) shielding materials with ultrahigh shielding effectiveness (SE) are highly desirable for high-speed electronic devices to attenuate radiated emissions. For hindering interference of their internal or external EMI fields, however, a metallic enclosure suffers from relatively low SE, band-limited anti-EMI responses, poor corrosion resistance, and non-adaptability to the complex geometry of a given circuit. Here, a broadband, strong EMI shielding response fabric is demonstrated based on a highly structured ferromagnetic graphene quartz fiber (FGQF) via a modulation-doped chemical vapor deposition (CVD) growth process. The precise control of the graphitic N-doping configuration endows graphene coatings on specifically designable quartz fabric weave with both high conductivity (3906 S cm⁻¹) and high magnetic responsiveness (a saturation magnetization of ≈0.14 emu g⁻¹ under 300 K), thus attaining synergistic effect of EMI shielding and electromagnetic wave (EMW) absorption for broadband anti-EMI technology. The large-scale durable FGQF exhibits extraordinary EMI SE of ≈107 dB over a broadband frequency (1–18 GHz), by configuring ≈20 nm-thick graphene coatings on a millimeter-thick quartz fabric. This work enables the potential for development of an industrial-scale, flexible, lightweight, durable, and ultra-broadband strong shielding material in advanced applications of flexible anti-electronic reconnaissance, antiradiation, and stealthy technologies.

The exposure sensitivity of negative tone electron beam resists based on a metal–organic ring can be tuned by subtle changes in the chemical composition. Inclusion of unsaturation in organic components and addition of heavy metal ions give a significant increase in write speed.

Abstract

A new class of electron bean negative tone resist materials has been developed based on heterometallic rings. The initial resist performance demonstrates a resolution of 15 nm half-pitch but at the expense of a low sensitivity. To improve sensitivity a 3D Monte Carlo simulation is used that utilizes a secondary and Auger electron generation model. The simulation suggests that the sensitivity can be dramatically improved while maintaining high resolution by incorporating appropriate chemical functionality around the metal–organic core. The new resists designs based on the simulation have the increased sensitivity expected and illustrate the value of the simulation approach.

Nature Electronics, Published online: 27 May 2022; doi:10.1038/s41928-022-00781-3

Heterostructures make light work of photodetection

Nature Electronics, Published online: 27 May 2022; doi:10.1038/s41928-022-00780-4

Two-dimensional materials stack up

Nature Electronics, Published online: 27 May 2022; doi:10.1038/s41928-022-00783-1

Methods to create van der Waals contacts between two-dimensional semiconductors and three-dimensional metals are helping to unleash the potential of two-dimensional devices.

A selective area reconstruction method is proposed for in-situ growth of high-quality customized monolayer graphene structures on copper substrates. The feature size of the fabricated arbitrary graphene structure is comparable with that of the photolithographic technology. This method provides a new approach for direct growth of high-quality, scalable, and high-precision graphene structures, which is promising for optoelectronic applications.

Abstract

High-quality customized monolayer graphene structures are a prerequisite for various applications such as electronics, optoelectronics, and energy devices. Top-down photolithography is the main method for graphene patterning, but it is greatly affected by complex manufacturing processes and residual photoresist. Recently, bottom-up methods based on catalyst or precursor patterning have been developed. Although these methods can achieve high-resolution graphene patterns, it is difficult to control the number of graphene layers and has a high defect density. Here, the authors propose a selective area reconstruction method for in-situ growth of high-quality monolayer graphene structures on copper substrates. The method utilizes selective oxidation and high-temperature reduction technologies, which can effectively regulate the surface characteristics of the copper substrate, thereby precisely controlling the nucleation and growth behavior of the customized graphene structure. The feature size of the fabricated graphene structure is less than 1 µm and it has high monolayer coverage and extremely low defect density. The performance of the photoluminescence device and photodetector based on the customized monolayer graphene structure is characterized. The method provides a new approach for the direct growth of high-quality, scalable, and high-precision functional graphene structures, which is expected to have great potential in the optoelectronic applications.

The electronic and magnetic response of the magnetic topological insulator MnBi₂Te₄ is shown to be controllable by manipulating the surface chemistry in epitaxial thin films. This results in a dramatic reversal of the sign of the anomalous Hall effect driven by a change in the effective film thickness due to the non-compensated magnetic moment.

Abstract

Understanding the effects of the interfacial modification to the functional properties of magnetic topological insulator thin films is crucial for developing novel technological applications from spintronics to quantum computing. Here, a large electronic and magnetic response is reported to be induced in the intrinsic magnetic topological insulator MnBi₂Te₄ by controlling the propagation of surface oxidation. It is shown that the formation of the surface oxide layer is confined to the top 1–2 unit cells but drives large changes in the overall magnetic response. Specifically, a dramatic reversal of the sign of the anomalous Hall effect is observed to be driven by finite thickness magnetism, which indicates that the film splits into distinct magnetic layers each with a unique electronic signature. These data reveal a delicate dependence of the overall magnetic and electronic response of MnBi₂Te₄ on the stoichiometry of the top layers. This study suggests that perturbations resulting from surface oxidation may play a non-trivial role in the stabilization of the quantum anomalous Hall effect in this system and that understanding targeted modifications to the surface may open new routes for engineering novel topological and magnetic responses in this fascinating material.

Charge-regulated field-effect transistors (CRFETs) with polarity-differentiated dielectric materials and a monolayer graphene channel are developed to mimic a reflex arc and pain modulation system of the spinal cord. By integrating actuators and memristors with CRFETs, reflex actions and pain sensation under noxious stimuli are realized, offering a new method to emulate the functionalities of the nervous system.

Abstract

The nervous system is a vital part of organisms to survive and it endows them with remarkable abilities, such as perception, recognition, regulation, learning, and decision-making, by intertwining myriad neurons. To realize such outstanding efficacies and functions, many artificial devices and systems have been investigated to emulate the operating principles of the nervous system. Here, an artificial reflex arc (ARA) and artificial pain modulation system (APMS) are proposed to imitate the unconscious behaviors of the spinal cord. Gd _x O _y - and Al _x O _y -based charge-regulated field-effect transistors (CRFETs) with a monolayer graphene channel are fabricated and adopted as inhibitory and excitatory synapses, respectively, under the same pulse signals to mimic the biological reflex arc through a connection with a poly(vinylidene fluoride-co-trifluoroethylene)-based actuator. Additionally, a memristor is integrated with a CRFET as the interneuron to regulate the Dirac point by controlling the voltage drop on the graphene channel, analogous to the descending pain-inhibition system in the spinal cord, to prevent excessive pain perception. The proposed ARA and APMS provide a significant step forward to realizing the functions of the nervous system, giving promising potential for developing future intelligent alarm systems, neuroprosthetics, and neurorobotics.

Nature Materials, Published online: 26 May 2022; doi:10.1038/s41563-022-01266-6

Thin films of BaTiO3 do not possess the same small switching fields and energies as the single-crystal form, hindering applications. Here, thin films are synthesized that enable switching for voltages <100 mV and fields <10 kV cm–1, and a pathway to subnanosecond switching is presented.

Heterobilayers of molybdenum and tungsten disulfide have mechanical and electrical properties that the individual layers lack.