Effects of electron-and hole-current hysteresis on trap characterization in organo-inorganic halide perovskite

Charge trap density and carrier mobility of perovskite materials are the critical properties of perovskite solar cells.The space charge limited current(SCLC)method,which measures a dark current–voltage(I-V)curve of a single-carrier device has found extensive use for studying the trap density and charge carrier mobility in perovskite materials.Herein,it was found that the electron-and hole-current in organo-lead perovskite-based single-carrier device undergoes significant hysteresis under forward and reverse scanning due to the mobile ions.In addition,it was also observed that measuring history has a detrimental effect on hysteresis resulting in possible overestimation or underestimation of the extracted electrical values from the SCLC measurement.In the forward/reverse scanning process,the mobile ionic defects enhance/shield the charge in the traps due to ionic charging/discharging,thereby increasing/reducing the interface barrier and net charge in the I-V scanning,which in turn affects the determination of transport properties of the carrier.These results raise quite a few doubts over the direct application of classical SCLC measurements for the accurate characterization of intrinsic transport properties of the mixed ionicelectronic perovskite.

二维碱金属金化物双金属烯半导体

将不同金属元素通过合金化形成二维材料(金属烯)对基础研究和纳米电子器件的实际应用具有重要意义,但目前鲜有金属烯材料是具有本征带隙的半导体.受离子晶体成键特征的启发,通过结构搜索、成键分析和高通量第一性原理计算,本文从2500多个双金属烯中筛选出一系列具有晶格动力学稳定和碱金属-金离子键的二维碱金属金化物双金属烯半导体.由于碱金属和金之间的大电负性差,其中32个碱金属金化物双金属烯是带隙范围为0.97~5.20 eV的半导体材料,而锂金双金属烯由于电负性差减小呈现出金属性.Bohn-Oppenheimer分子动力学模拟表明19个双金属烯在室温下结构稳定有利于实际应用.这项研究为设计双金属烯半导体提供了指导,并揭示了二维金属合金中成键行为和电子结构性质间的关联.

范德华材料Ta_(2)Ni_(3)Te_(5)中巨大的面内振动和输运各向异性

目前,Ta_(2)M3Te_(5)(M=Ni,Pd)层状范德华化合物可承载各种奇异电子态,且具有表现出非平凡输运现象的诱人潜力,因而重新引起人们的兴趣.其特征有Luttinger液体、量子自旋霍尔效应、高阶拓扑结构和超导电性.本文中,我们报道了单晶Ta_(2)Ni_(3)Te_(5)的合成,并揭示了其在每个具有准一维键合特征的层内的多重平面内各向异性.我们的技术结合了偏振拉曼光谱、角度分辨光电发射光谱、第一性原理计算和电/磁输运测量的能力.链状低对称层状结构的声子振动产生了高度各向异性的拉曼响应,不同的链内和链间键合特性导致电子带和声学声子的各向异性色散,这共同导致[100]和[001]方向之间的巨大平面内迁移率各向异性(2000%).这一结果与我们的电输运和霍尔效应测量结果相符.因此,沿不同平面内方向的输运行为也表现出不同的温度和磁场依赖性.本工作揭示的丰富的面内各向异性表明,Ta_(2)Ni_(3)Te_(5)是探索新型二维各向异性电子动力学的一个很有前途的平台,在下一代纳米电子器件中具有潜在的应用前景.

Larger in-plane upper critical field and superconducting diode effect observed in topological superconductor candidate InNbS_(2)nanoribbons

Recently,the coexistence of topology and superconductivity has garnered considerable attention.Specifically,the dimensionality of these materials is crucial for the realization of topological quantum computation.However,the naturally grown materials,especially with one-dimensional feature that exhibits the coexistence of topology and superconductivity,still face challenges in terms of experimental realization and scalability,which hinders the fundamental research development and the potential to revolutionize quantum computing.Here,we report the first experimental synthesis of quasi-one-dimensional InNbS_(2)nanoribbons that exhibit the coexistence of topological order and superconductivity via a chemical vapor transport method.Especially,the inplane upper critical field of InNbS_(2)nanoribbons exceeds the Pauli paramagnetic limit by more than 2.2 times,which can be attributed to the enhanced spin-orbit coupling and the weakened interlayer interaction between the NbS_(2)layers induced by the insertion of In atoms,making InNbS_(2)exhibit spin-momentum locking similar to that of monolayer NbS_(2).Moreover,for the first time,we report the superconducting diode effect in a quasi-one-dimensional superconductor system without any inherent geometric imperfections.The measured maximum efficiency is manifested as 14%,observed atμ0H≈±60 mT,and we propose that the superconducting diode effect can potentially be attributed to the presence of the nontrivial topological band.Our work provides a platform for studying exotic phenomena in condensed matter physics and potential applications in quantum computing and quantum information processing.

Bioinspired hybrid patches with self-adhesive hydrogel and piezoelectric nanogenerator for promoting skin wound healing

Wound management is a crucial measure for skin wound healing and is significantly important to maintaining the integrity of skins and their functions.Electrical stimulation at the wound site is a compelling strategy for skin wound repair.However,there has been an urgent need for wearable and point-of-care electrical stimulation devices that have self-adhesive and mechanical properties comparable to wound tissue.Herein,we develop a bioinspired hybrid patch with self-adhesive and piezoelectric nanogenerator(HPSP)for promoting skin wound healing,which is composed of a mussel-inspired hydrogel matrix and a piezoelectric nanogenerator based on aligned electrospun poly(vinylidene fluoride)nanofibers.The device with optimized modulus and permeability for skin wear can self-adhere to the wound site and locally produce a dynamic voltage caused by motion.We show that the HPSP not only promotes fibroblast proliferation and migration in vitro,but also effectively facilitates the collagen deposition,angiogenesis,and re-epithelialization in vivo with the increased expressions of crucial growth factors.The HPSP reduces the wound closure time of full-thickness skin defects by about 1/3,greatly accelerating the healing process.This patch can serve as wearable and real-time electrical stimulation devices,potentially useful in clinical applications of skin wound healing.

Theoretical investigation of gold based model catalysts

With potential applications in various fields, gold related catalysts have received intensive attentions. In the past decade, mechanisms of gold catalysis for low-temperature CO oxidation, NOx oxidation/reduction, selective oxidation of alcohols have been investigated both experimentally and theoretically based on model catalysts using free or supported gold nanoparticles and single crystal gold surfaces. In this short review, we summarize recent theoretical studies on molecular oxygen activation process, water or hydroxyl involved oxidation reaction, and also the effect of local structure on the reactivity and selectivity.

Magnetic logic inverter from crossed structures of defect-free graphene with large unsaturated room temperature negative magnetoresistance

Introducing defects into graphene has been widely utilized to realize the negative magnetoresistanee(MR)effect in graphene.However,the reported graphene negative MR exhibits only^10%under 10 T at room temperature to date,which extremely limits the resolution of future spintronics devices.Moreover,intentional defect introduction can also cause unintentional degradation in graphene's intrinsic properties.In this paper,we report a magnetic logic inverter based on a crossed structure of defect-free graphene,resulting in a substantial gain of 4.81 mV/T while exhibiting room temperature operation.This crossed structure of graphene shows large unsaturated room temperature negative MR with an enhancement of up to 1,000%at 9 T.A transition behavior between negative and positive MR is observed in this crossed structure and the transition temperature can be tuned by a ratio of the conductivity between in-plane and out-of-plane transport.Our results open an intriguing path for future two-dimensional spintronics device applications.

Chiral transfer-dictated self-assembly of chiral block copolymers

Chiral structures not only exist in nature widely,they also emerge in artificial systems,attracting myriad attentions due to their excellent mechanical,optical,electrical,and magnetic properties.Self-assembly of chiral block copolymers(BCPs*),where at least one block consists of chiral centers,represents a facile strategy to form helical/spiral/network structures with a controlled chirality.Usually,morphological chirality of BCP*assemblies was closely associated with molecular and conformational chirality of the chiral block.Generally,chiral assemblies arose from molecular chirality of BCPs*,transferring up in the assembly process and dictated the chirality at a higher hierarchical level.In contrast,notwithstanding similar assemblies could be observed from achiral BCPs under certain conditions,both left-and right-handed ones were usually observed simultaneously without a preference.Moreover,unique feature of BCPs*to access to controllable chiral assemblies affords an opportunity to prepare advanced functional materials.Herein,we dedicated a review on assembly of BCPs*into chiral assemblies in bulk/films,selective solvents,and confined spaces.The chiral transfer process in these assembly scenarios were discussed and highlighted as a key contributor to morphological chirality.Functionalities and representative applications of BCP*assemblies were also described,followed by present challenges and future prospects of BCP*self-assembly.

层间Cu^(+)离子重排诱导体系超导转变

层间离子插层的层状材料表现出多样有趣的物理和化学特性.为了获得奇特的二维材料,离子客体对晶体的掺杂和调控在材料科学中得到广泛应用.然而,在离子插层层状材料的研究中,由层间结构变化所引起的性质研究较少.因此,在本文中我们展示了由于Cu_(0.65)NbS_(2)纳米片的新型层间结构导致的超导性.随着维度的降低,层间铜离子的占位从体相结构时的单一四面体位点转变为混合四面体位点,导致原本的普通金属态转变成超导体.值得注意的是,材料的超导转变温度具有强烈的厚度依赖性,并且随厚度变化呈火山曲线,展现出了与纯NbS2体系不同的随样品层数变化关系.操控层间离子的排列方式将成为促进二维材料领域新本征性质研究的重要方法之一.

High-metallic-phase-concentration MO1-xWxS2 nanosheets with expanded interlayers as efficient electrocatalysts

In most cases, layered transition metal dichalcogenides （LTMDs）, containing metallic phases, show electrochemical behavior different from their semiconductor counterparts. Typically, two-dimensional layered metallic 1T-MoS2 demonstrates better electrocatalytic performance for water splitting compared to its 2H counterpart. However, the characteristics of low metallic phase concentration and poor stability limit its applications in some cases. Herein, we demonstrate a simple and efficient bottom-up wet-chemistry strategy for the large-scale synthesis of nanoscopic ultrathin Mo1-xWxS2 nanosheets with enlarged interlayer spacing and high metallic phase concentration. Our characterizations, including X-ray absorption fine structure spectroscopy （XAFS）, high-angle annular dark-field- scanning transmission electron microscopy （HAADF-STEM）, and X-ray photoelectron spectroscopy （XPS） revealed that the metallic ultrathin ternary Mo1-xWxS2 nanosheets exhibited distorted metal-metal bonds and a tunable metallic phase concentration. As a proof of concept, this optimized catalyst, with the highest metallic phase concentration （greater than 90%）, achieved a low overpotential of about -155 mV at a current density of -10 ma/cm^2, a small Tafel slope of 67 mV/dec, and an increased turnover frequency （TOF） of 1.3 H2 per second at an overpotential of -300 mV （vs. reversible hydrogen electrode （RHE））, highlighting the importance of the metallic phase. More importantly, this study can lead to a facile solvothermal route to prepare stable and high-metallic- phase-concentration transition-metal-based two-dimensional materials for future applications.

2D hetero-structures based on transition metal dichalcogenides:fabrication,properties and applications

Recently,two dimensional transition metal dichalcogenides MX_2(M = Mo,W,etc; X = S,Se,Te) have ignited immense interests because of their unique structural and physical properties for the potential applications in the nano-optoelectronics,valley-spintronics etc. In terms of the structural compatibility and van der Waals interaction,two dimensional(2D) MX_2 layers can be fabricated into various lateral and vertical hetero-structures. The atomically-thin hetero-structures comprising different layered MX_2 provide a new platform for exploring fundamental physics and device technologies with unprecedented phenomenon and extraordinary functionalities. In this review,we report the recent progress about the fabrication,properties and applications of 2D hetero-structures based on transition metal dichalcogenides.

Planar-symmetry-breaking induced antisymmetric magnetoresistance in van der Waals ferromagnet Fe_(3)GeTe_(2)

Recently discovered magnetic van der Waals(vdW)materials provide an ideal platform to explore low-dimensional magnetism and spin transport.Its vdW interaction nature opens up unprecedented opportunities to build vertically stacked heterostructures with novel properties and functionalities.By engineering the planar structure as an alternative degree of freedom,herein we demonstrate an antisymmetric magnetoresistance(MR)in a vdW Fe_(3)GeTe_(2)flake with a step terrace that breaks the planar symmetry.This antisymmetric MR originates from a sign change of the anomalous Hall effect and the continuity of the current transport near the boundary of magnetic domains at the step edge.A repeatable domain wall due to the unsynchronized magnetization switching is responsible for this sign change.Such interpretation is supported by the observation of field-dependent domain switching,and the step thickness,temperature,and magnetic field orientation dependent MR.This work opens up new opportunities to encode magnetic information by controlling the planar domain structures in vdW magnets.