Jing Zhang

A 2D heterostructure-based memtransistor is designed to emulate the Bienenstock–Cooper–Munro (BCM) theory, since this structure not only induces spontaneous forgetting process but also offers another gate-tunable forgetting effect. BCM learning rule is perfectly demonstrated on this memtransistor using triplet-STDP. Furthermore, high-order spatiotemporal recognition is achieved in a feedforward neuron network based on the memtransistor.

Abstract

The Bienenstock, Cooper, and Munro (BCM) theory of synaptic plasticity is regarded as the most precise model of the synapse, and is more compatible with neuromorphic computing. However, the development in BCM synaptic modification is rather limited since the memristive devices used to emulate the BCM lack tunable forgetting rate. Compared with memristors, memtransistors provide another gate-tunable freedom degree, which will help to modulate the forgetting rate. In this work, the authors demonstrate a perfect BCM learning rule based on the 2D heterostructure memtransistor through using triplet-spike timing dependent plasticity model. Two critical characteristics of the BCM rule, sliding frequency threshold and enhanced depression effect, are perfectly presented due to their spontaneous/gate-assistant forgetting effect. The experimental results are extremely consistent with the BCM learning rule and suggest the potential application of 2D memtransistors in high-order spatiotemporal recognition.

Arbitrary graphene microelectrodes are directly patterned on fallen leaves in ambient air by ultraviolet ultrafast laser. The graphene microelectrodes on leaves exhibit superior electrical conductivity compared with their synthetic polymer counterparts. Due to unique hierarchical porous structures, flexible graphene micro-supercapacitors on leaves show excellent performance that can be utilized for green wearable electronics.

Abstract

The development of green flexible micro-supercapacitors (MSCs) is one of the biggest challenges in future wearable electronics. Flexible MSCs are mainly produced from non-biodegradable synthetic polymers, resulting in massive electronic waste. Moreover, complex multi-step fabrication increases their production cost. Here, the direct fabrication of highly conductive, intrinsically flexible, and green microelectrodes from naturally fallen leaves in ambient air using femtosecond laser pulses without any additional materials is reported. Hierarchically porous graphene is patterned on different types of leaves via a facile, mask-less, scalable, and one-step laser writing. Leaves consist of biominerals, which decompose into inorganic crystals that serve as nucleation sites for the growth of 3D mesoporous few-layer graphene. The femtosecond laser-induced graphene (FsLIG) microelectrodes formed on leaves have lower sheet resistance (23.3 Ω sq⁻¹) than their synthetic polymer counterparts and exhibit an outstanding areal capacitance (34.68 mF cm⁻² at 5 mV s⁻¹) and capacitance retention (≈99% after 50 000 charge/discharge cycles). The FsLIG MSCs on a single leaf could easily power a light-emitting diode or a table clock and could be applied in wearable electronics, smart houses, and Internet of Things.

Electrochromic displays provide reversible switch of multiple colors and long-term bistability. The first example of Zn anode-based electrochromic displays having 2D color space tunability is presented to display multiple colors traversing a 2D International Commission on Illumination regional color space. These findings accelerate future electrochromic display technology that brings the full-color tunability in a single electrochromic device within reach.

Abstract

Electrochromic devices with a wide color gamut distribution have long been sought after for non-emissive display technologies. The current state-of-the-art multicolor electrochromic displays utilize a single electrochromic layer, which restricts their color tunability within a linear or curved segment scope in International Commission on Illumination (CIE) color space and thus leads to limited color hues. Herein, it is demonstrated vivid electrochromic displays with broadened color hues via fabricating Zn-based multicolor electrochromic displays having 2D CIE color space tunability. In addition, it is revealed that a Fabry–Perot nanocavity structure can further tune the color hues via altering the coordinate of the 2D CIE color space. It is known that this is the first demonstration of 2D CIE color space tunability realization from a single transparent or reflective electrochromic device. These findings represent a novel strategy for fabricating multicolor electrochromic displays and are expected to advance the development of electrochromic displays.

Here, a strategy is proposed for fabricating ultrastretchable MoS₂ photoreceptors based on multilayer MoS₂. The ten-layer MoS₂ photodetector on polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene (SEBS) elastomer can withstand ≈50% tensile strain and presents 32 times higher photoresponsivity than that of monolayer MoS₂. Large-area bilayer MoS₂ array is demonstrated and is capable of working as artificial photoreceptors to control a mechanical hand under 16% tensile strain.

Abstract

2D materials have been widely applied in flexible electronics but only with limited stretchability, because the metal-halide bonding is so strong that the materials’ electronic properties will be severely influenced upon tensile strain. Here, a strategy is proposed for the fabrication of ultrastretchable MoS₂ photoreceptors based on chemical vapor deposition-grown or manually stacked multilayer MoS₂. Strain-dependent spectroscopic comparisons of multilayer versus monolayer MoS₂ indicate that the strain transfer is suppressed from bottom to top layers owing to interlayer sliding, which is consistent with the density functional theory and molecular dynamics simulations. Thus, the optoelectronic properties of multilayer MoS₂ can withstand larger mechanical strain than monolayer MoS₂. Leveraging this mechanical feature, ten-layer MoS₂ photodetector is fabricated on polystyrene-b-poly (ethylene-co-butylene)-b-polystyrene elastomer, withstanding ≈50% tensile strain and presenting 32 times higher photoresponsivity than that of monolayer MoS₂ under the same stretching condition. Based on large-area bilayer MoS₂ film, 5 × 5 stretchable photodetector array is demonstrated and is capable of working as artificial photoreceptors to control a robotic hand under 16% tensile strain, showing great potential in applications for 2D material-based electronic skin.

Van der Waal (VdW) doping is investigated and applied to germanium sulfide transistors using layered black phosphorus. This VdW doping results in the observation of resonant tunneling at room temperature coupled with a conductivity switch to n-type semiconductor. Van der Waal doping can be a promising method for future nanoelectronics applications.

Abstract

van der Waals semiconductors have proven to be exceptional for electronic and photonic applications. Although most research is extensively focused on some transition metal dichalcogenides materials (MX₂) such as MoS₂, WS₂, WS_e2, and MoSe₂, studies on 2D metal monochalcogenides such as germanium sulfide (GeS) has been widely under investigated, mainly due to the high contact resistance GeS devices exhibit. Here, a van der Waals field-effect transistor (VdW-FET) based on GeS is investigated and resonant tunneling behavior is shown at room temperature due to VdW doping via black phosphorus (BP), evident by the observation of multiple decades of negative differential resistance (NDR) during doping transient state. These NDR decades are caused by confinement of carriers inside the double barrier quantum well, which allows tunneling to occur for discrete energy levels. Moreover, a noticeable conductivity switch from a low p-type to a high n-type is observed, with a conductivity enhancement of 2 orders of magnitude compared to pristine GeS devices. The underlying mechanism behind the observed NDR and the conductivity switch is discussed and it is shown that these phenomena are likely caused by phosphorus doping due to BP sublimation, evident by the detected P-Ge Raman peak in the measured Raman spectra. The results can open doors for electrical oscillators and switching devices for the next generation of nanoelectronics.

Active hydrogen evolution reaction (HER) at heterophase boundaries between semiconducting 2H and metallic 1T’ phases in large-scale MoTe₂ is reported. Despite the small area ratio of the 1D heterophase boundary to the basal plane, HER is improved up to a turnover frequency of 317 s⁻¹ at the 1D geometry. Kelvin probe force microscopy demonstrates a sharp band bending for the HER.

Abstract

The phase engineering of transition metal dichalcogenides (TMDs) is considered a promising strategy for promoting efficient catalysis, such as the hydrogen evolution reaction (HER). While theoretical studies predict the presence of catalytically active atomic sites at heterophase boundaries in TMDs, conventional bulk HER measurements are not able to precisely explore these 1D heterophase regions for HER. Here, one reports on active HER occurring at heterophase boundaries between the semiconducting 2H and metallic 1T’ phases in large-scale MoTe₂ grown via chemical vapor deposition. Microreactors are used to investigate the local HER at varying lengths of 1D heterophase boundaries, and the results are systematically compared with the HER performance at the pristine basal planes of MoTe₂. Despite the small area ratio between the 1D heterophase boundary and the open region for local HER, a clear improvement in HER is observed with a turnover frequency of 317 s^–1. The Kelvin probe force microscopy determines a surface potential difference of 50 mV across the heterophase boundary, which supports sharp band bending and local charge accumulation as the basis for the TMDs’ efficient electrochemical catalysis.

Nature Nanotechnology, Published online: 02 December 2021; doi:10.1038/s41565-021-01023-x

Square-centimetre scale, multilayer superlattice structures based on atomically thin two-dimensional chalcogenide monolayers enable the realization of excitonic metamaterials.

Nature Nanotechnology, Published online: 03 December 2021; doi:10.1038/s41565-021-01029-5

Mid-infrared pulses stimulate fast neutralization of photocharged colloidal nanocrystals, which suppresses blinking of a single nanocrystal’s photoluminescence.

Nature Nanotechnology, Published online: 18 November 2021; doi:10.1038/s41565-021-01020-0

Dense, short hydrophobic nanochannels have been restacked from two-dimensional quantum sheets to achieve both high areal and volumetric capacitance in thick electrodes under ultrahigh rates.

Nature Nanotechnology, Published online: 29 November 2021; doi:10.1038/s41565-021-00994-1

Although quantum physics underpins the behaviour of nanoscale objects, its role in nanoscience has been mostly limited to determining the static, equilibrium properties of small systems. This Review describes seminal developments and new directions for the explicit exploitation of quantum coherence in nanoscale systems, a research area termed quantum-coherent nanoscience.

Nature Nanotechnology, Published online: 29 November 2021; doi:10.1038/s41565-021-01014-y

In moiré superlattice van der Waals magnetic materials, competing interactions emerge and can stabilize new magnetic states. Here, stacking-dependent interlayer exchange interactions in small-twist-angle CrI3 bilayers yield an ordered ground state with coexisting ferromagnetic and antiferromagnetic regions.

A facile strategy is developed to construct Ru SACs with tunable microenvironments by employing NiFe-LDH with different cation vacancies as supports. The Ru-O coordination environments and electronic configurations of Ru₁ can be easily tailored by the vacancy regulation. Hence, isolated Ru atoms anchored by M^III vacancies facilitate the desorption of benzaldehyde, thus leading to higher efficiency of benzyl alcohol oxidation.

Abstract

Single-atom catalysts (SACs) with rationally designed microenvironments (defined as coordination environments and electronic configurations) show superior catalytic activity, selectivity, and stability in a majority of reactions. However, the construction of isolated SACs with definite microenvironments to understand the microenvironment–activity relationship is still challenging. Herein, a facile strategy is developed to construct a series of Ru SACs with tunable geometric and electronic structures by employing NiFe-layered double hydroxides (LDH) with different cation vacancies (M^II or M^III) as supports. Detailed spectroscopic characterizations and theoretical calculations reveal that the Ru-O coordination environments and electronic configurations of single-atomic Ru can be easily tailored by the vacancy regulation. As a result, isolated Ru atoms anchored by M^III vacancies (denoted as Ru₁/LDH-V_III) with Ru-O-Ni coordination environments facilitate the desorption of benzaldehyde, thus leading to higher efficiency of benzyl alcohol oxidation with a superior turnover frequency of 1331 h⁻¹.

The heterogenous MoSe₂/N-doped carbon nanoarrays demonstrate a brilliant performance as K-ion batteries anode materials with greatly enhanced reversibility. The as-formed heterointerface greatly weakens the KSe bond of the discharge product (K₂Se) by optimizing its geometric structure, leading to the easy regeneration of the MoSe bond. The K-ion storage mechanism and structure-performance relationship are further clarified during de-/potassiation.

Abstract

Owing to the lower price and higher safety, developing high-performance K-ion batteries (KIBs) is of great significance as an alternative to Li-ion batteries. High-energy-density MoSe₂ has been identified as a promising anode material for KIBs; however, its electrochemical reversibility remains a big challenge. Herein, heterogenous MoSe₂/N-doped carbon nanoarrays demonstrate a brilliant performance as KIBs anode materials. The as-formed hetero-interface weakens the KSe bond of discharged products (K₂Se), the length of KSe bond is stretched by 3.9% with an enlargement of 19.2% in angle compared with pure K₂Se, greatly promoting the regeneration of MoSe bond during charge. Moreover, the atomically inter-overlapping feature leads to an expanded MoSe₂ interlayer distance of 1.20 nm that enables a much faster K-ion diffusion. Consequently, this nanoarray delivers an unprecedented K-ion storage performance, that is, a capacity of 402 mAh g⁻¹ at 0.2 A g⁻¹ over 200 cycles, and a long cycle life over 1000 cycles at 1.0 A g⁻¹ with 307 mAh g⁻¹ capacity retention.

Van der Waals (vdW) materials are an indispensable part of functional device technology. Recently, the search for magnetic vdW materials has intensified due to the realization of magnetism in 2D. However, metallic magnetic vdW systems are still uncommon and they rarely show high-mobility charge carriers. Using chemical reasoning, it is found that TaCo₂Te₂ is an air-stable, high-mobility, magnetic vdW material.

Abstract

Van der Waals (vdW) materials are an indispensable part of functional device technology due to their versatile physical properties and ease of exfoliating to the low-dimensional limit. Among all the compounds investigated so far, the search for magnetic vdW materials has intensified in recent years, fueled by the realization of magnetism in 2D. However, metallic magnetic vdW systems are still uncommon. In addition, they rarely host high-mobility charge carriers, which is an essential requirement for high-speed electronic applications. Another shortcoming of 2D magnets is that they are highly air sensitive. Using chemical reasoning, TaCo₂Te₂ is introduced as an air-stable, high-mobility, magnetic vdW material. It has a layered structure, which consists of Peierls distorted Co chains and a large vdW gap between the layers. It is found that the bulk crystals can be easily exfoliated and the obtained thin flakes are robust to ambient conditions after 4 months of monitoring using an optical microscope. Signatures of canted antiferromagntic behavior are also observed at low-temperature. TaCo₂Te₂ shows a metallic character and a large, nonsaturating, anisotropic magnetoresistance. Furthermore, the Hall data and quantum oscillation measurements reveal the presence of both electron- and hole-type carriers and their high mobility.

Through the construction of a W/Cr₂Ge₂Te₆ heterostructure with annealing treatment, the Curie temperature of Cr₂Ge₂Te₆ is raised above 150 K with strong perpendicular magnetic anisotropy, which is attributed to the interfacial orbital hybridization. Due to the weak interlayer coupling, the interfacial enhancement can be effective in long distance. The enhanced ferromagnetism can be controlled by spin-orbit torque with low current density.

Abstract

Ferromagnetic semiconductors discovered in 2D materials open an avenue for highly integrated and multifunctional spintronics. The Curie temperature (T _C) of existing 2D ferromagnetic semiconductors is extremely low and the modulation effect of their magnetism is limited compared with their 2D metallic counterparts. The interfacial effect is found to effectively manipulate the 3D magnetism, providing a unique opportunity for tailoring the 2D magnetism. Here, it is demonstrated that the T _C of a 2D ferromagnetic semiconductor Cr₂Ge₂Te₆ (CGT) can be enhanced by 130% (from ≈65 K to above 150 K) when adjacent to a tungsten layer. The interfacial W–Te bonding contributes to the T _C enhancement with a strong perpendicular magnetic anisotropy, guaranteeing efficient magnetization switching by the spin-orbit torque with a low current density at 150 K. Distinct from the rapid attenuation in conventional magnets, the interfacial effect exhibits a weak dependence on CGT thickness and a long-distance effect (more than 10 nm) due to the weak interlayer coupling inherent to 2D magnets. This work not only reveals a unique interfacial behavior in 2D materials, but also advances the process toward practical 2D spintronics.

A perovskite single crystal is grown in solution via a hydrothermal reaction. Through a co-doping strategy of both Na⁺ and Yb³⁺, a dual-band emission comprising both visible and near-infrared (NIR) is activated by self-trapped excitons and lanthanide ions, respectively. Intriguingly, a long-lasting afterglow at NIR band (≈7200 s) and a simultaneous photochromism are both observed after ceasing the excitation.

Abstract

Near-infrared (NIR) afterglow is keenly sought in emerging areas including deep-tissue imaging and night-vision surveillance, while only few successes in powder phosphors are achieved through solid-state calcination. In this work, a perovskite single crystal, namely Cs₂Na_0.2Ag_0.8InCl₆:Yb³⁺, is grown in solution via a simple hydrothermal reaction. Through a co-doping strategy involving both Na⁺ and Yb³⁺, dual-band emission in the visible and NIR region is activated by self-trapped excitons (STE) and lanthanide ions, respectively. Importantly, the total photoluminescence quantum yield (PL QY) of both bands is boosted to ≈82%. Intriguingly, a long-lasting afterglow at the NIR band (≈7200 s) and a simultaneous photochromism is observed after ceasing the excitation. Importantly, the transparency of crystals exhibit a pronounced contrast in the decoloration process, enabling a quantitative analysis of photochromism at varied temperatures. On the other hand, the transparent crystals enable the design of a light-storage battery free of reabsorption, featuring a linear power output with crystal loading. This work proposes a new paradigm to quantitatively correlate the afterglow traps to photochromism, opening many possibilities to practical applications of NIR-afterglow transparent crystals.

Nature Nanotechnology, Published online: 10 November 2021; doi:10.1038/s41565-021-01024-w

2D materials grow large

Nature Nanotechnology, Published online: 12 November 2021; doi:10.1038/s41565-021-01046-4

Author Correction: Tuning of the Berry curvature in 2D perovskite polaritons

Nature Nanotechnology, Published online: 15 November 2021; doi:10.1038/s41565-021-01015-x

Nonlocal noise thermometry enables experimental probing of energy transport in emergent states of matter and devices in low dimensions.

Nature Nanotechnology, Published online: 15 November 2021; doi:10.1038/s41565-021-01004-0

A dual-coupling-guided growth mechanism enables the realization of wafer-scale single-crystal WS2 on vicinal a-plane sapphire.

Two dimensional van der Waals ferromagnets with honeycomb structures are expected to host the bosonic version of Dirac particles in their magnon excitation spectra. Using inelastic neutron scattering, we study spin wave excitations in polycrystalline CrCl 3 , which exhibits ferromagnetic honeycomb layers with antiferromagnetic stackings along the c -axis. For comparison, polycrystal samples of CrI 3 with different grain sizes are also studied. We find that the powder-averaged spin wave spectrum of CrCl 3 at T  = 2 K can be adequately explained by the two dimensional spin Hamiltonian including in-plane Heisenberg exchanges only. The observed excitation does not exhibit noticeable broadening in energy, which is in remarkable contrast to the substantial broadening observed in CrI 3 . Based on these results, we conclude that the ferromagnetic phase of CrCl 3 hosts massless Dirac magnons and is thus not topological.

For the first time, EMW absorbers based on VB-group NbS₂ nanosheets achieved via a one-step solvothermal method are successfully prepared. The remarkable EMW absorption performance can also be reflected in the tunable frequency bands (C-, X-, and Ku-bands). It opens up a new way for the development of broadband absorbing materials for electromagnetic wave absorption.

Abstract

VB-Group transition metal disulfides (TMDs) are considered excellent materials for electromagnetic wave (EMW) absorption because of their good conductivity and abundant active sites located at their edges and substrates, as compared with VIB-Group TMDs. Herein, for the first time, EMW absorbers based on VB-Group NbS₂ nanosheets by using a facile one-step solvothermal method are successfully prepared. The minimum reflection loss (RL_min) can reach up to 43.85 dB with an effective absorption bandwidth of 6.48 GHz (11.52–18.00 GHz). The remarkable EMW absorption performance can also be reflected in the tunable frequency bands (C-, X-, and Ku-bands), which is achieved by adjusting the contents of materials. Furthermore, the influence of the content of 2H-phase and 1T-phase in NbS₂ on the EMW absorption performance is systematically investigated. The hierarchical hollow-sphere structure of NbS₂ promotes dielectric loss and the multiple reflection and absorption of EMW, and enhances the impedance matching and synergistic attenuation ability. This work demonstrates that the bottleneck of effective absorbing frequency band of single-component dielectric EMW absorbing materials could be broken through, and paves a novel path towards developing broadband absorbing materials in EMW absorption.

Nature Nanotechnology, Published online: 08 November 2021; doi:10.1038/s41565-021-00999-w

So far, only conventional field emitters based on a bulk W needle have achieved atomic resolution in electron microscopy. Here, through the integration of a passive collimator structure and micromanipulation-based alignment of the support needle, a LaB6 nanowire emitter yields stable emission under moderate vacuum conditions and allows for atomic-resolution images and high energy resolution.

To emulate the entire human visual system at the single device level, a multifunctional optoelectronic synapse based on ferroelectric α-In₂Se₃/GaSe vdW heterostructure is elaborately designed. Visual perception, logic functions, and memory are integrated into the device. The study shed light on creating a sophisticated artificial visual system analogous to that of humans and break the bottleneck of current image recognition technology.

Abstract

The development of optoelectronic synapses can provide an important breakthrough toward creating a sophisticated and adaptable artificial visual system analogous to that of humans. However, it remains a great challenge to implement the various functions of the biological visual neuromorphic system at the single device level. Intriguingly, 2D van der Waals (vdW) heterostructure may offer a platform to address the issue. Here, a novel multifunctional synaptic device based on ferroelectric α-In₂Se₃/GaSe vdW heterojunction is proposed to emulate the entire biological visual system. Essential synaptic behaviors are observed in response to light and electrical stimuli; additionally, the retina-like selectivity for light wavelengths and the achievement of Pavlov's dog experiment demonstrate the device's capacity for processing complex electrical and optical inputs. Beyond the optoelectronic synaptic behaviors, the device incorporates memory and logic functions analogous to those in the brain's visual cortex. The results of artificial neural network simulations show that the vdW heterojunction-based device is completely capable of performing logic operations and recognizing images with a high degree of accuracy. The study indicates that versatile devices with a rationally designed construction have great potential for efficiently processing complex visual information and may simplify the design of artificial visual systems.