Memristive feature and mechanism induced by laser-doping in defect-free 2D semiconductor materials

Memristors as non-volatile memory devices have gained numerous attentions owing to their advantages in storage,in-memory computing, synaptic applications, etc. In recent years, two-dimensional(2D) materials with moderate defects have been discovered to exist memristive feature. However, it is very difficult to obtain moderate defect degree in 2D materials, and studied on modulation means and mechanism becomes urgent and essential. In this work, we realized memristive feature with a bipolar switching and a configurable on/off ratio in a two-terminal MoS_(2) device(on/off ratio ~100), for the first time, from absent to present using laser-modulation to few-layer defect-free MoS_(2)(about 10 layers), and its retention time in both high resistance state and low resistance state can reach 2×10^(4) s. The mechanism of the laser-induced memristive feature has been cleared by dynamic Monte Carlo simulations and first-principles calculations. Furthermore, we verified the universality of the laser-modulation by investigating other 2D materials of TMDs. Our work will open a route to modulate and optimize the performance of 2D semiconductor memristive devices.

Fabrication of ultra-high strength magnesium alloys over 540 MPa with low alloying concentration by double continuously extrusion

We prepare a new type of patented biodegradable biomedical Mg-Nd-Zn-Zr(JDBM)alloy system and impose double continuously extrusion(DCE)processing.The lowest processing temperature is 250℃for JDBM-2.1Nd and 310℃for JDBM-2.8Nd,which increases with the Nd concentration.The highest yield strength of 541 MPa is achieved in JDBM-2.1 Nd samples when extruded at 250℃and the elongation is about 3.7%.Moreover,the alloy with a lower alloying element content can reach a higher yield strength while that with a higher alloying element content can reach a larger elongation after DCE processing.However,when extruded under the same conditions,the alloy with a higher alloying contents exhibits better tensile properties.

High-performance junction field-effect transistor based on black phosphorus/β-Ga2O3 heterostructure

Black phosphorous(BP),an excellent two-dimensional(2D)monoelemental layered p-type semiconductor material with high carrier mobility and thickness-dependent tunable direct bandgap structure,has been widely applied in various devices.As the essential building blocks for modern electronic and optoelectronic devices,high quality PN junctions based on semiconductors have attracted widespread attention.Herein,we report a junction field-effect transistor(JFET)by integrating narrow-gap p-type BP and ultra-wide gap n-typeβ-Ga2O3 nanoflakes for the first time.BP andβ-Ga2O3 form a vertical van der Waals(vdW)heterostructure by mechanically exfoliated method.The BP/β-Ga2O3 vdW heterostructure exhibits remarkable PN diode rectifying characteristics with a high rectifying ratio about 107 and a low reverse current around pA.More interestingly,by using the BP as the gate andβ-Ga2O3 as the channel,the BP/β-Ga2O3 JFET devices demonstrate excellent n-channel JFET characteristics with the on/off ratio as high as 107,gate leakage current around as low as pA,maximum transconductance(gm)up to 25.3μS and saturation drain current(IDSS)of 16.5μA/μm.Moreover,it has a pinch-off voltage of–20 V and a minimum subthreshold swing of 260 mV/dec.These excellent n-channel JFET characteristics will expand the application of BP in future nanoelectronic devices.

Realization of flexible in-memory computing in a van der Waals ferroelectric heterostructure tri-gate transistor

Combining logical function and memory characteristics of transistors is an ideal strategy for enhancing computational efficiency of transistor devices.Here,we rationally design a tri-gate two-dimensional(2D)ferroelectric van der Waals heterostructures device based on copper indium thiophosphate(CuInP_(2)S_(6))and few layers tungsten disulfide(WS_(2)),and demonstrate its multi-functional applications in multi-valued state of data,non-volatile storage,and logic operation.By co-regulating the input signals across the tri-gate,we show that the device can switch functions flexibly at a low supply voltage of 6 V,giving rise to an ultra-high current switching ratio of 107 and a low subthreshold swing of 53.9 mV/dec.These findings offer perspectives in designing smart 2D devices with excellent functions based on ferroelectric van der Waals heterostructures.

An integrated portable bio-monitoring system based on tough hydrogels for comprehensive detection of physiological activities

Advanced soft ion-conducting hydrogels have been developed rapidly in the integrated portable health monitoring equipment due to their higher sensitivity,sensory traits,tunable conductivity,and stretchability for physiological activities and personal healthcare detection.However,traditional hydrogel conductors are normally susceptible to large deformation and strong mechanical stress,which leads to inferior electro-mechanical stability for real application scenarios.Herein,a strong ionically conductive hydrogel(poly(vinyl alcohol)-boric acid-glycerol/sodium alginate-calcium chloride/electrolyte ions(PBG/SC/EI))was designed by engineering the covalently and ionically crosslinked networks followed by the salting-out effect to further enhance the mechanical strength and ionic conductivity of the hydrogel.Owing to the collective effects of the energy-dissipation mechanism and salting-out effect,the designed PBG/SC/EI with excellent structural integrity and robustness exhibits exceptional mechanical properties(elongation at break for 559.1%and tensile strength of 869.4 kPa)and high ionic conductivity(1.618 S·m^(-1)).As such,the PBG/SC/EI strain sensor features high sensitivity(gauge factor=2.29),which can effectively monitor various kinds of human motions(joint motions,facial micro-expression,faint respiration,and voice recognition).Meanwhile,the hydrogel-based Zn||MnO_(2)battery delivers a high capacity of 267.2 mAh·g^(-1)and a maximal energy density of 356.8 Wh·kg^(-1)associated with good cycle performance of 71.8%capacity retention after 8000 cycles.Additionally,an integrated bio-monitoring system with the sensor and Zn||MnO_(2)battery can accurately identify diverse physiological activities in a real-time and non-invasive way.This work presents a feasible strategy for designing high-performance conductive hydrogels for highly-reliable integrated bio-monitoring systems with excellent practicability.

Diamond: asymmetry leads to continuous hardening

Naturally occurring and synthetic materials are often polycrystalline comprising various species of grain boundaries(GBs),many of which are randomly oriented.It is known that GBs play a pivotal role in affecting a broad range of material properties,and the nature of GBs is dedicated by grain orientation,growth history and processing conditions.

Anomalous refinement and uniformization of grains in metallic thin films

When a laser beam writes on a metallic film,it usually coarsens and deuniformizes grains because of Ostwald ripening,similar to the case of annealing.Here we show an anomalous refinement effect of metal grains:A metallic silver film with large grains melts and breaks into uniform,close-packed,and ultrafine(~10 nm)grains by laser direct writing with a nanoscale laser spot size and nanosecond pulse that causes localized heating and adaptive shock-cooling.This method exhibits high controllability in both grain size and uniformity,which lies in a linear relationship between the film thickness(h)and grain size(D),D∝h.The linear relationship is significantly different from the classical spinodal dewetting theory obeying a nonlinear relationship(D∝h5/3)in common laser heating.We also demonstrate the application of such a silver film with a grain size of~10.9 nm as a surface-enhanced Raman scattering chip,exhibiting superhigh spatial-uniformity and low detection limit down to 10-15 M.This anomalous refinement effect is general and can be extended to many other metallic films.

All-atomristor logic gates

The atomristor(monolayer two-dimensional(2D)-material memristor)is competitive in high-speed logic computing due to its binary feature,lower energy consumption,faster switch response,and so on.Yet to date,all-atomristor logic gates used for logic computing have not been reported due to the poor consistency of different atomristors in performance.Here,by studying band structures and electron transport properties of MoS2 atomristor,a comprehensive memristive mechanism is obtained.Guided by the simulation results,monolayer MoS2 with moderated defect concentration has been fabricated in the experiment,which can build atomristors with high performance and good consistency.Based on this,for the first time,MoS2 all-atomristor logic gates are realized successfully.As a demonstration,a half-adder based on the logic gates and a binary neural network(BNN)based on crossbar arrays are evaluated,indicating the applicability in various logic computing circumstances.Owing to shorter transition time and lower energy consumption,all-atomristor logic gates will open many new opportunities for next-generation logic computing and data processing.

In situ observation of the pseudoelasticity of twin boundary

Twin boundary(TB)is a special and fundamental internal interface that plays a key role in altering the mechanical and physical properties of materials.However,the atomistic deformation mechanism of TB re-mains under debate,of which the most concerned aspect is how TB would affect the mechanical strength and plasticity of a material.Herein,we introduce our new discovery that the pseudoelastic strain of a TB can recover with decomposition and escape of pile-up dislocations,demonstrated by imposing a sponta-neous pseudoelastic deformation with recoverable plastic bending strain up to 5.1%on a TB.We found that the steps on the curved TB gradually annihilated during the migration of the TB,which was in-duced by the slip of decomposition dislocations on the TB.The TB not only provides local strain harden-ing through interaction with dislocations during the loading stage but also acts as a channel for the fast movement of decomposition dislocations during the recovery stage.Beside,the TB can maintain excellent pseudoelasticity under a multicycle bending test,which may play an important role in improving the fa-tigue resistance of materials.These findings could open up a new avenue for optimizing the mechanical properties of materials by manipulating their twin boundaries at the nanoscale.

Novel intelligent devices: Two-dimensional materials based memristors

Two-dimensional(2D)materials with atomic thickness,non-volatile resistive switching feature and compatibility with the semiconducting technology are naturally a good media of memristors.2D materials-based memristors with excellent performance,low-power consumption and high integration density can be integrated with other circuit components to implement the complicate logic computing,which will become a key driving force for the development of artificial intelligence.

Boosting acidic water oxidation performance by constructing arrays-like nanoporous Ir_(x)Ru_(1−x)O_(2) with abundant atomic steps

The fabrication of electrocatalysts with high activity and acid stability for acidic oxygen evolution reaction(OER)is an urgent need,yet extremely challenging.Here,we report the design and successful fabrication of a high performance self-supported cogwheel arrays-like nanoporous Ir_(x)Ru_(1−x)O_(2) catalyst with abundant atomic steps for acidic OER using a facile alloy-spinningelectrochemical activation method that allows large-scale fabrication.The obtained Ir_(x)Ru_(1−x)O_(2) catalysts merely need overpotentials of 211 and 295 mV to deliver catalytic current densities of 10 and 300 mA·cm^(−2) in 0.5 M H_(2)SO_(4),respectively,and can sustain constant OER electrolysis for at least 140 h at a high current density of 300 mA·cm^(−2).Further density functional theory(DFT)calculations uncover that such high intrinsic activities mainly originate from the largely exposed high-index atomic step planes,which markedly lower the limiting potential of the rate-determining step(RDS)of OER.These findings provide an insight into the exploration of high performance electrocatalysts,and open up an avenue for further developing the state-of-theart Ir and/or Ru-based catalysts for large-scale practical applications.

Plasma tailoring in WTe_(2)nanosheets for efficiently boosting hydrogen evolution reaction

2D transition metal dichalcogenides(TMDs)have been considered as promising non-precious electrocatalysts for the hydrogen evolution reaction(HER).However,their limited active sites and poor electric conductivity pose a significant hurdle to their HER performance,resulting in a large overpotential.Here,we report the defect engineering in ultrathin tungsten telluride(WTe_(2))nanosheets with semimetal nature to improve hydrogen evolution effectively.We find that the oxygen plasma etching imposes a cutting effect on WTe_(2)nanosheets,resulting in a large number of tungsten vacancies.Particularly,the sample after plasma treatment for 10 min shows a feather-like structure with an overpotential of 251m V at 10 m A/cm~2and a Tafel slope of 94 m V/dec,which is 4 times lower than the Tafel slope of pristine nanosheets.Further first-principles calculations shed light on the evolution of defect-rich WTe_(2)nanosheets and offer rational explanation to their superiority in efficient hydrogen evolution.

Ultrafast growth of high-quality large-sized GaSe crystals by liquid metal promoter

Growth of high-quality large-sized crystals using the traditional chemical vapor transport(CVT)or vertical Bridgman(VB)technique is costly and time-consuming,limiting its practical industrial application.Here,we propose an ultrafast crystal growth process with low energy consumption and capability of producing crystals of excellent quality,and demonstrate that large-sized GaSe crystals with a lateral size of 0.5 to 1 cm can be obtained within a short period of 5 min.X-ray diffraction(XRD)and scanning transmission electron microscopy(STEM)studies clearly indicate that the as-grown crystals have a good crystallinity.To further show the potential application of the resulting GaSe crystals,we fabricate the few-layer GaSe-based photodetector,which exhibits low dark current of 21 pA and fast response of 34 ms under 405 nm illumination.Our proposed technique for rapid crystal growth could be further extended to other metallenes with low-melting point,such as Bi-,Sn-,In-,Pb-based crystals,opening up a new avenue in fulfilling diverse potential optoelectronics applications of two-dimensional(2D)crystals.

Synthesis of Meta Symmetric 1T'-WTe2 Using an Edge-Induced Mechanism

Lattice symmetry is vital to the properties of two-dimensional(2D)materials,yet their fixed symmetry cannot meet the increasing requirements in highly eficient and programmable electrical transport.If the structural diversity of 2D materals,as demon-strated by 1T'-WTez,is improved without any phase transition or structural reconstruction,excellent metallic 1T'-WTez would be possibly used for inte-grated devices.Here,we realized meta symmetry of 1T'-WTez by using an edge-induced mechanism,which is recognized as the combination of the intrin-sic C2v symmetry and sixfold axes.On account of the dynamically controlled growth,the meta symmetric 1T'-WTez with^94.9%purity is obtained for the first time.Meta symmetry will also keep the intrinsic electrical properties of 1T'-WTez over the node.Such meta symmetry could not only enrich the structural diversity of 1T'-WTez,but also be extended to other low-symmetry 2D materials,which would be promising for customized circuits and devices.

Growth of 2D MoP single crystals on liquid metals by chemical vapor deposition

Two-dimensional(2 D) transition metal phosphides(TMPs) are predicted with many novel properties and various applications. As a member of TMPs family, molybdenum phosphide(MoP) exhibits many exotic physicochemical properties. However, the synthesis of high-quality2 D MoP single crystals is not reported due to the lack of reliable fabrication method, which limits the exploration of 2 D MoP. Here, we report the growth of high-quality ultrathin MoP single crystals with thickness down to 10 nm on liquid metals via chemical vapor deposition(CVD). The smooth surface of liquid Ga is regarded as a suitable growth substrate for producing 2 D MoP single crystals. The Mo source diffuses toward the Ga surface due to the high surface energy to react with phosphorus source, thus to fabricate ultrathin MoP single crystals. Then, we study the second harmonic generation(SHG) of 2 D MoP for the first time due to its intrinsic noncentrosymmetric structure. Our study provides an new approach to synthesize and explore other 2 D TMPs for future applications.

Ni(Ⅱ) Ternary Complex Based on Antimicrobial Drug Enoxacin: Synthesis and Biological Properties

First Ni(Ⅱ)ternary complex using the quinolone antibacterial agent enoxacin(HEn)as ligand and 1,10-phenanthroline as co-ligand has been synthesized and characterized.It is a mononuclear structure,in which enoxacin acts as a bidentate ligand bound to the metal through the ketone oxygen and a carboxylate oxygen atom.The complex exhibited good binding propensity to human and bovine serum albumin proteins having relatively high binding constants(6.40×10^(4) and 7.12×10^(4),respectively).The investigation of the interaction of the complex with calf-thymus(CT)DNA has been performed with UV and circular dichroism(CD)spectroscopies,indicating that they bind to CT DNA probably by the intercalative binding mode.The binding constant(K_(b))of the complex with CT DNA calculated with UV is 2.03×10^(5),which is higher than that of free enoxacin drug(2.09×10^(4))and even higher than that of typical intercalation indicator(1.23×10^(5))of ethidium bromide(EB).Fluorescence competitive studies with EB have revealed that the complex exhibited the ability to displace the DNA-bound EB using the intercalative binding site.In addition,the antimicrobial activity showed that the complex exhibited a little bit good inhibition(MIC=1.843μg•mL^(-1))against B.subtilis than free HEn.

Metallic interface induced by electronic reconstruction in crystalline-amorphous bilayer oxide films

Extraordinary electronic properties can emerge at the interfaces between metal oxides[1-10].Interfacial behaviors have enabled a wide range of applications from electronic communication,energy conversion and storage,to data processing and memory.In recent years,unprecedented progress has been made in exploring and exploiting the emergent and/or enhanced properties of these interfaces,and it is becoming clear that interface engineering provides a new opportunity for advanced devices in the near future.The capability of using interfaces to manipulate material properties offers an effective means to achieve intriguing phenomena.