Piezo‐Phototronic Effect for Enhanced Flexible MoS2/WSe2 van der Waals Photodiodes

The recent discoveries of transition‐metal dichalcogenides (TMDs) as novel 2D electronic materials hold great promise to a rich variety of artificial van der Waals (vdWs) heterojunctions and superlattices. Moreover, most of the monolayer TMDs become intrinsically piezoelectric due to the lack of structural centrosymmetry, which offers them a new degree of freedom to interact with external mechanical stimuli. Here, fabrication of flexible vdWs p–n diode by vertically stacking monolayer n‐MoS₂ and a few‐layer p‐WSe₂ is achieved. Electrical measurement of the junction reveals excellent current rectification behavior with an ideality factor of 1.68 and photovoltaic response is realized. Performance modulation of the photodiode via piezo‐phototronic effect is also demonstrated. The optimized photoresponsivity increases by 86% when introducing a −0.62% compressive strain along MoS₂ armchair direction, which originates from realigned energy‐band profile at MoS₂/WSe₂ interface under strain‐induced piezoelectric polarization charges. This new coupling mode among piezoelectricity, semiconducting, and optical properties in 2D materials provides a new route to strain‐tunable vdWs heterojunctions and may enable the development of novel ultrathin optoelectronics.     

无铅压电陶瓷材料研究进展

系统分析了无铅压电陶瓷材料的研究现状,在此基础上,对(Bi, Na)TiO3-Ba(Zr,Ti)O3及CaBi4Ti4O15(CBT)基两类无铅材料进行了研究。结果表明:非化学计量掺杂及A位空位的存在有助于提高(Bi, Na)TiO3-Ba(Zr,Ti)O3材料的压电活性,通过引入适量的Sn,在该体系中得到了d33高达196 pC/N的材料。通过A位小离子复合取代及引入A位空位的方法,大大提高CaBi4Ti4O15材料的压电性能,居里温度及高温电阻率。得到了居里温度高达866℃,d33为20 pC/N的优质高温无铅压电材料。     

2D Layered Dipeptide Crystals for Piezoelectric Applications

2D piezoelectric materials such as transition metal dichalcogenides are attracting significant attention because they offer various benefits over bulk piezoelectrics. In this work, the fabrication of layered biomolecular crystals of diphenylalanine (FF) obtained via a co-assembly of l,l - and d,d - enantiomers of FF monomers is reported. Their crystal structure, thermal and chemical stabilities, and piezoelectric properties are investigated. Single crystal X-ray diffraction results show that FF enantiomers are arranged in the form of bilayers consisting of monomers with alternating chirality packed into a tape-like monoclinic structure belonging to a polar space group P2₁. Each bilayer ( ≈ 1.5 nm thick) demonstrates strong out-of-plane piezoelectricity (d₃₃  ≈  20 pm V⁻¹) that is almost an order of magnitude higher than in the archetypical piezoelectric material quartz. The grown crystals demonstrate better thermal and chemical stabilities than self-assembled hexagonal FF nanotubes studied in the past. Piezoelectric bilayers, being held via weak aromatic interaction in the bulk crystals, can be exfoliated by mechanical or chemical methods, thus resulting in a 2D piezoelectric material, which can find various applications in biocompatible and ecologically friendly electromechanical microdevices, such as sensors, actuators, and energy harvesting elements used in implantable and wearable electronics.     

Ferroelectric Polarization-Enhanced Performance of Flexible CuInP2S6 Piezoelectric Nanogenerator for Biomechanical Energy Harvesting and Voice Recognition Applications

2D piezoelectric materials have strong intrinsic piezoelectricity and superior flexibility, which are endowed with huge potential to develop piezoelectric nanogenerators (PENGs). However, there are few attempts to investigate the energy harvesting of 2D ferroelectric materials. Herein, an enhanced output performance is reported by ferroelectric polarization in a PENG with exfoliated 2D ferroelectric CuInP₂S₆ (CIPS). Specifically, the polarized CIPS-based PENG produces a short-circuit current of 760 pA at 0.85% tensile strain, which is 3.8 times higher than that of unpolarized CIPS-based PENG. Systematical PFM and Raman analysis reveal that the ferroelectric polarization remarkably reinforces the effective piezoelectric constant of CIPS nanoflakes and boosts the in-plane migration and out-of-plane hopping of copper ions, which is the main reason for the enhancement of output performance. Furthermore, the CIPS-based PENG can not only be utilized to harvest biomechanical energy such as wrist joints movement, but also exhibits a potential for a voice recognition system integrated with deep learning technology. The classification accuracy of a series of letter sounds is as high as 96%. This study commendably broadens the application scope of 2D materials in micro-nano energy and intelligent sensors, which will have profound implications for exploring wearable nanoelectronic devices.     

Flexible Piezoelectric Nanocomposite Generators Based on Formamidinium Lead Halide Perovskite Nanoparticles

Organic–inorganic lead halide perovskite materials have recently attracted much attention in the field of optoelectronic devices. Here, a hybrid piezoelectric nanogenerator based on a composite of piezoelectric formamidinium lead halide perovskite (FAPbBr₃) nanoparticles and polydimethylsiloxane polymer is fabricated. Piezoresponse force spectroscopy measurements reveal that the FAPbBr₃ nanoparticles contain well‐developed ferroelectric properties with high piezoelectric charge coefficient (d₃₃) of 25 pmV⁻¹. The flexible device exhibits high performance with a maximum recordable piezoelectric output voltage of 8.5 V and current density of 3.8 μA cm⁻² under periodically vertical compression and release operations. The alternating energy generated from nanogenerators can be used to charge a capacitor and light up a red light‐emitting diode through a bridge rectifier. This result innovatively expands the feasibility of organic–inorganic lead halide perovskite materials for application in a wide variety of high‐performance energy harvesting devices.     

形状参数对Cymbal执行器压电性能的影响

研究金属端帽及压电陶瓷的形状参数对压电复合执行器 Cymbal压电性能的影响。Cymbal执行器由在厚度方向极化的压电陶瓷片 (PZT- 5 A)夹在两个薄的黄铜端帽之间 ,每一个端帽的内表面都有一个圆台形空穴。Cymbal执行器的纵向等效压电常数 de33与金属端帽的直径 de2 、内腔深度 te、黄铜箔的厚度 tb及压电陶瓷片的直径dp、厚度 tp有关     

Organization of Organic Molecules with Inorganic Nanoparticles: Hybrid Nanodiodes

A monolayer of inorganic nanoparticles and a monolayer of organic molecules have been electrostatically assembled in sequence. Such assemblies or organizations exhibit electrical rectification. When the sequence of the organization is reversed, the direction of rectification becomes opposite. In both n‐type ZnO/organic and organic/n‐ZnO assemblies, electron flow is favorable from the n‐ZnO nanoparticle to the (electron‐accepting) organic molecule. While the individual components do not show any rectification, substitutes of the organic molecule tune electrical rectification. Junctions between a p‐type ZnO nanoparticle and an electron‐donating metal phthalocyanine favor current flow in the nanoparticle‐to‐phthalocyanine direction. The rectification in a junction between a nanoparticle and an organic molecule is due to the parity between free carriers in the former component and the type of carrier‐accepting nature in the latter one. By observing electrical rectification with the tip of a scanning tunneling microscope, organic/inorganic hybrid nanodiodes or rectifiers on the molecular/nanoscale have been established.     

Declamped Piezoelectric Coefficients in Patterned 70/30 Lead Magnesium Niobate–Lead Titanate Thin Films

Lateral subdivision of blanket piezoelectric thin films increases the functional properties through both increased domain wall mobility and declamping of the intrinsic response. This work presents the local effects of substrate declamping on the piezoelectric coefficient d _33,f of 300 nm thick, rhombohedral, {001}‐oriented lead magnesium niobate–lead titanate thin films at the 70/30 composition (70PMN–30PT). Films grown by chemical solution deposition on platinized Si substrates are patterned into strip structures ranging from 0.75 to 9 µm in width. The longitudinal piezoelectric coefficient, d _33,f, is interrogated as a function of position across the patterned structures by three approaches: finite element modeling, piezoresponse force microscopy, and nanoprobe synchrotron X‐ray diffraction. It is found that d _33,f increases from the clamped value of 40–50 to ≈160 pm V^?1 at the free sidewall under 200 kV cm^?1 excitation. The sidewalls partially declamp the piezoelectric response 500–600 nm into the patterned structure, raising the piezoelectric response at the center of features with lateral dimensions less than 1 µm (3:1 width to thickness aspect ratio). The normalized data from all three methods are in excellent agreement, with quantitative differences providing insight to the field dependence of the piezoelectric coefficient and its declamping behavior.     

压电材料的发展及应用

对压电学作了历史地回顾之后.本文概括地叙述了国内外,特别是我所的压电材料的发展以及它们的各式各样的应用.最后介绍了压电陶瓷的发展趋势.     

A Piezotronic and Magnetic Dual-Gated Ferroelectric Semiconductor Transistor

Piezotronics is the coupling effect of the piezoelectric and semiconductor properties; however, the piezoelectric constant of the piezoelectric semiconductor is relatively small while the ferroelectric materials with large piezoelectric constant typically possess weak semiconductor properties, thus limiting the effective coupling coefficient of the piezotronic materials and devices. Here, a piezotronics and magnetic dual-gated ferroelectric semiconductor transistor (PM-FEST) is fabricated by Terfenol-D, aluminum oxide (Al₂O₃), and ferroelectric semiconductor α-In₂Se₃, which has a large piezoelectric coefficient, room-temperature ferroelectricity, and dipole locking. The charge carrier transport and corresponding drain current of the PM-FEST can be directly modulated by either the applied magnetic field or external strain. At a low magnetic field (<200 mT), the maximum current on/off ratio of α-In₂Se₃ based PM-FEST is as high as 1700%. Compared with traditional piezotronic devices, the PM-FEST demonstrates a higher gauge factor (2.3 × 10⁴) than that of the piezoelectric semiconductors. This work provides a possibility of realizing magnetism-modulated electronics in semiconductors by exploiting the coupling of piezotronics and magnetostriction.     

驻极体的研究现状

驻极体是电介质物理、材料科学、传感器工程及生物医学的重要交叉学科。近年来，驻极体在生物驻极体、驻极体的应用及有机驻极体的非线性光学效应等方面取得了瞩目的进展。文章就上述几个问题，从材料制备、实验方法和驻极体的应用等方面进行了综述。     

The Relationship between Structural and Electrical Characteristics in Perylenecarboxydiimide‐Based Nanoarchitectures

The controlled assembly of the prototypical n‐type organic semiconductor N,N′‐1H,1H‐perfluorobutyl dicyanoperylenecarboxydiimide (PDIF‐CN₂) into ordered nanoarchitectures and the multiscale analysis of the correlation between their structural and their electrical properties is reported. By making use of the Langmuir–Blodgett (LB) technique, monolayers of PDIF‐CN₂ arranged in upright standing molecular packing on different substrates are formed. Postdeposition thermal treatment makes it possible to trigger a reorganization into layered ultrathin crystalline nanostructures, exhibiting structural and photophysical properties similar to those of microscopic crystals obtained by solvent‐induced precipitation. The controlled engineering of these molecular architectures on surfaces enables us to identify both a dependence of the monolayer resistance on the molecular tilt angle in vertical junctions and a pronounced charge‐transport anisotropy with enhanced transport along the π–π stacking direction of the PDI core. While a charge carrier mobility for electrons as high as 10^–2 cm² V^–1 s^–1 is determined in monolayer field‐effect transistors for the in‐plane direction, being the highest yet reported value for a n‐type LB monolayer, the out‐of‐plane mobility measured by conductive atomic force microscopy in multilayered structures is found to be one order of magnitude lower.     

Ba (Ti0.8Zr0.2)O3-(Ba0.7Ca0.3)TiO3无铅陶瓷的显微结构和压电性能

采用传统固相反应制备出了高压电常数的Ba(Ti0.8 Zr0.2)O3-(Ba0.7Ca0.3)TiO3 (BZT-xBCT)无铅压电陶瓷材料,研究了BCT含量对于体系结构、压电与介电性能的影响规律.结果表明,x=0.45～0.60时,BZTxBCT系统处于准同型相界附近,BZT-xBCT陶瓷时主晶相为钙钛矿相结构,当x＞0.50时,出现少量的第二相CaTiO3.当x=0.50时,陶瓷的性能达到最佳,其介电常数ε、压电常数d33、机电耦合系数kp、机械品质因数Qm、频率系数Np分别为2 900,385 pC/N,0.456,124和2 740 Hz·m.由此可认为位于准同型相界附近的BZT-xBCT是一类很有前途的无铅压电材料.     

霍耳位移法测量压电陶瓷的压电系数

提出了一种利用霍耳位移传感器测量压电陶瓷的横向压电系数的新方法。该方法利用压电陶瓷的逆压电效应,对压电陶瓷施加一定大小的电压,使其在垂直电场方向上产生微小形变,利用霍耳位移传感器法测量这一微小位移,得到不同电压驱动下压电陶瓷相应的伸长量,通过计算得出该材料的压电系数。实验表明,该方法简单可靠,精确度高,实验结果符合预期。     

铌镁酸铅-钛酸铅铁电体准同型相界附近的压电性能研究

采用固相合成法制备了准同型相界附近的PMN-PT铁电陶瓷,对其介电和压电性能进行了研究,并讨论了不同掺杂对陶瓷的晶粒尺寸,介电常数,压电系数和机电耦合系数的影响,分析了不同掺杂取代位置对陶瓷的介电和压电性能的影响。发现这一体系陶瓷材料的压电性能与其晶粒的大小有一定的对应关系,同时在这一体系的掺杂后的影响可以较好地用传统PZT系统中的软硬掺杂解释。     

Ionic Current Rectification in Soft‐Matter Diodes with Liquid‐Metal Electrodes

A soft‐matter‐based diode composed of hydrogel and liquid metal (eutectic gallium indium, EGaIn) is presented. The ability to control the thickness, and thus resistivity, of an oxide skin on the metal enables rectification. First, a simple model system with liquid‐metal/electrolyte‐solution/Pt interfaces is characterized. The electrically insulating oxide skin on the EGaIn electrode is reduced or oxidized further depending on the direction of the bias, thereby allowing unidirectional ionic current. The forward current of the diode increases as the conductivity of the electrolyte increases, whereas backward current depends on the pH of the medium in contact with the insulating oxide layer on the EGaIn electrode. As a result, the diode shows a higher rectification ratio (defined as the ratio of forward to backward current measured at the same absolute bias) with more conductive electrolyte at neutral pH. Replacement of the liquid electrolyte solution with a hydrogel improves the structural stability of the soft diode. The rectification performance also improves due to the increased ionic conductivity by the gel. Finally, a diode composed entirely of soft materials by replacing the platinum electrode with a second liquid‐metal electrode is presented. Contacting each liquid metal with a polyelectrolyte gel featuring different pH values provided asymmetry in the device, which is necessary for rectification. A hydrogel layer infused with a strong basic polyelectrolyte removes the insulating oxide layer, allowing one interface with the EGaIn electrode to be conductive regardless of the direction of bias. Thus, the oxide layer at the other interface rectifies the current.     

Mg掺杂ZnO电子结构与压电性能的第一性原理研究

采用第一性原理计算方法研究了掺杂不同Mg（r(Mg),摩尔比）的ZnO材料的电子结构与压电性能。研究发现,随着r(Mg)的增加,ZnO晶格常数c与a的比值（c/a）减小,材料禁带宽度增大。当r(Mg)=0.3时,其带隙达到最大值（为1.493 eV）。态密度与差分电荷密度计算结果表明,其带隙增大的原因是导带中Zn-3d态向高能端移动。Mg的引入有助于提升ZnO材料的压电性能,其压电系数从本征的1.302 72 C/m²提升至1.355 88 C/m²,压电系数的提高可能来源于四方因子c/a数值减小引起的结构畸变。     

K4CuNb8O23对K0.5Na0.5NbO3-Bi0.5Na0.5TiO3-LiSbO3压电陶瓷结构及性能的影响

采用固相反应法制备了0.96(0.99K0.5Na0.5.5NbO3-0.01Bi0.5Na0.5TiO3)-0.04¨SbO3-xK4CuNb8O23(0≤x≤3.00％)(简称KNN-BNT-LS-KCN)无铅压电陶瓷,研究了其晶体结构、压电、介电以及铁电性质。结果表明,KCN的加入使所制陶瓷的晶体结构从四方相转变...     

Giant Piezoelectric Coefficients in Relaxor Piezoelectric Ceramic PNN‐PZT for Vibration Energy Harvesting

It is well known that the piezoelectric performance of ferroelectric Pb(Zr,Ti)O₃ (PZT) based ceramics is far inferior to that of ferroelectric single crystals due to ceramics' polycrystalline nature. Herein, it is reported that piezoelectric stress coefficient e₃₃ = 39.24 C m^?2 (induced electric displacement under applied strain) in the relaxor piezoelectric ceramic 0.55Pb(Ni_1/3Nb_2/3)O₃–0.135PbZrO₃–0.315PbTiO₃ (PNN‐PZT) prepared by the solid state reaction method exhibits the highest value among various reported ferroelectric ceramic and single crystal materials. In addition, its piezoelectric coefficient d₃₃* = 1753 pm V^?1 is also comparable with that of the commercial Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ (PMN‐PT) piezoelectric single crystal. The PNN‐PZT ceramic is then assembled into a cymbal energy harvester. Notably, its maximum output current at the acceleration of 3.5 g is 2.5 mA_pp, which is four times of the PMN‐PT single crystal due to the large piezoelectric e₃₃ constants; while the maximum output power is 14.0 mW, which is almost the same as the PMN‐PT single crystal harvester. The theoretical analysis on force‐induced power output is also presented, which indicates PNN‐PZT ceramic has great potential for energy device application.     

Printing 2D Conjugated Polymer Monolayers and Their Distinct Electronic Properties

Recently, 2D monolayer films of conjugated polymers have gained increasing attention owing to the preeminence of 2D inorganic films that exhibit unique optoelectronic and mechanical properties compared to their bulk analogs. Despite numerous efforts, crystallization of semiconducting polymers into highly ordered 2D monolayer films still remains challenging. Herein, a dynamic‐template‐assisted meniscus‐guided coating is utilized to fabricate continuous, highly ordered 2D monolayer films of conjugated polymers over a centimeter scale with enhanced backbone π–π stacking. In contrast, monolayer films printed on solid substrates confer upon the 1D fiber networks strong alkyl side‐chain stacking at the expense of backbone packing. From single‐layers to multilayers, the polymer π‐stacks change from edge‐on to bimodal orientation as the film thickness reaches ≈20 nm. Spectroscopic and cyclic voltammetry analysis reveals an abrupt increase in J‐aggregation and absorption coefficient and a decrease in bandgap and highest occupied molecular orbital level until critical thickness, possibly arising from the straightened polymer backbone. This is corroborated by an abrupt increase in hole mobility with film thickness, reaching a maximum of 0.7 cm² V^?1 s^?1 near the critical thickness. Finally, fabrication of chemical sensors incorporating polymer films of various thicknesses is demonstrated, and an ultrahigh sensitivity of the ≈7 nm thick ultrathin film (bilayers) to 1 ppb ammonia is shown.