ZnO压电薄膜的生长与应用

本文实验研究了ZnO压电薄膜的生长与表征,运用XRD和SEM测试了磁控溅射生长的ZnO压电薄膜的C轴择优取向生长情况和晶粒质量,比较了Si、覆盖在si基底上的Al薄膜和SixNy薄膜三种材料衬底以及退火处理对ZnO薄膜的结晶质量的影响.还开发了仍然采用Al作为底电极但用一层SixNy薄膜与ZnO层隔离的MEMS压电器件的微制造工艺,以满足生长高质量的ZnO压电薄膜并与CMOS工艺兼容的要求.     

用光声技术测量ZnO薄膜的压电系数

本文报导了用光声技术测量溅射 ZnO 薄膜的压电系数,介绍了用来测量 ZnO 薄膜压电系数的理论分析和实验方法。本实验所得压电系数 e_(33)、e_(31)的值分别为0.817C/m~2和-0.431C/m~2,与 ZnO 单晶的值相比是合理的。     

类石墨烯二维材料及光电器件应用研究进展

二维层状材料是具有单原子层或几个原子层厚度的平面材料,有着特殊的物理化学性能,在光电功能器件、吸附与分离、催化等领域具有重要应用前景,是目前国际研究的前沿和热点领域之一。其中,石墨烯是最先受到人们重视的二维材料,随即以过渡金属硫化物为主的类石墨烯二维光电功能材料也被广泛研究。近年来黑磷的发现也极大促进了二维光电材料的研究和发展。二维光电材料中石墨烯及类石墨烯硫化物的研究及其光电功能器件应用现状进行简单综述,并对其应用趋势进行展望,为光电材料研究领域的研究提供参考。     

电阻率梯度PZT/ZnO压电复合陶瓷的结构与电性能

研制了具有电阻率和压电系数梯度的PZT/ZnO压电陶瓷,其本身也是一类独石型梯度功能压电陶瓷驱动器(FGMPA),并且它所需的驱动电场比La-PZT/Fe-PZT FGMPA低.分别用电子探针(EPMA)、X衍射(XRD)和扫描电镜(SEM)查证了其组分、相结构和显微结构的梯度分布.结果表明,显微结构及电性能的梯度分布,主要是由Zn2+的扩散及其在PZT晶界富集造成的,它也是使PZT层中与界面相邻的部分区域电阻率下降的原因.XRD证实了在PZT层中ZnO第二相的存在.     

ZnO纳米棒/石墨烯异质结构的应用研究进展

ZnO纳米棒具有优异的光学性质,石墨烯具有优良的电学性质并且可变形,制备出高质量ZnO纳米棒/石墨烯异质结构能够发挥两者协同效应,有望在高性能光电子器件中实现重要应用。综述了近几年来国内外关于ZnO纳米棒/石墨烯异质结构的最新研究进展,重点包括该结构的各种制备技术及特点,该结构在发光器件、太阳能电池器件、光电探测器以及光催化剂等方面的应用研究进展,最后展望了其未来发展趋势和研究重点。     

低温剥离法制备高性能石墨烯/ZnO复合材料

采用氧化石墨和七水合硫酸锌作为初始反应物, 在低温下(80℃)合成了氧化石墨/ZnO, 然后通过低温剥离法制备了高质量石墨烯/ZnO (GNS/ZnO)复合材料. 采用X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、热重分析仪(TG)、X射线光电子能谱(XPS)、拉曼光谱(RS)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等分析手段对石墨烯/ZnO样品进行了表征. 结果表明: 氧化石墨还原彻底, 纳米ZnO成功地负载到了石墨烯上, 有效地减少了石墨烯片层间的团聚现象. 通过对ZnO和石墨烯/ZnO荧光性能测试, 结果表明: 石墨烯/ZnO发生了荧光淬灭现象, 在光电子领域拥有广阔的应用前景.     

~(60)Coγ射线辐照单层石墨烯的损伤效应

石墨烯是一种在常温下拥有极低的电阻率、极高的电子迁移率和高透光性的零带隙能带结构的新型碳材料,由于石墨烯优异的电学特性、光学特性和光电性能使它为研制下一代超快、高频、宽光谱光电器件提供了可能,目前已有许多基于石墨烯的光电探测器件研究,若将此类器件未来应用于航天器必有巨大优势。基于此本工作首先用化学气相沉积法制备了单层多晶石墨烯,然后进行了伽马射线辐照单层石墨烯实验,并用拉曼光谱表征了辐照前后石墨烯微观结构变化,对辐照后石墨烯的缺陷间平均距离,缺陷密度等进行了分析,辐照使单层石墨烯产生缺陷,出现无序的sp~3杂化结构。此研究可为石墨烯光电器件在外层空间中的应用打下基础,为其他空间环境因素对石墨烯的影响研究提供借鉴参考。     

石墨烯及其相关材料的技术发展全景分析

正石墨烯,一种碳原子紧密堆积成单层二维蜂窝状晶格结构的炭质二维材料,以其超高的比较面积[单层石墨烯比表面积理论计算为2 630m~2/g)、优异的电子迁移率(20 000cm~2/(V·s)]、高的热导率(导热系数高达5 300W/m·K)、超强的力学性能和良好的生物相容性,成为了学术界以及产业界研究和开发的热点,它可以应用于理论物理实验平台、纳米电子器件、超导材料、储能和产能器件、显微滤网、传感器和生物医药等领域。     

固贴式薄膜体声波谐振器性能受压电材料的影响分析

利用Math CAD软件对固贴式薄膜体声波谐振器(SMR-FBAR)器件建立数学模型进行仿真,分析了不同压电薄膜材料和厚度,不同电极材料和厚度对FBAR器件谐振特性的影响。采用射频磁控溅射方法制备氮化铝(AlN)薄膜,利用扫描探针显微镜中的压电力显微镜(PFM)模块对AlN薄膜的压电性能进行了测试。得到主要结论为:复合FBAR的谐振频率因为增加了电极厚度因素相比理想FBAR的谐振频率偏低;压电材料的机电耦合系数对器件带宽起决定性作用,器件的机电耦合系数正比于材料的机电耦合系数;AlN具有较高的压电系数,可以有效提升器件性能,增大带宽,适合作为压电薄膜材料;采用小尺寸压电薄膜和电极厚度有益于提高器件的频率。     

应用于体声波谐振器的ZnO薄膜结构和电学特性

采用直流磁控溅射的方法制备了ZnO压电薄膜,并在双面抛光的熔融石英基片上制备了高次谐波体声波谐振器.x射线衍射结果显示ZnO压电薄膜C轴择优取向明显,衍射峰半高宽为0.1624°,显示出较好的结晶质量;扫描电镜分析观察到ZnO垂直于基片表面的柱形晶粒结构和较平滑的薄膜表面.体声波器件的电学测试结果显示器件具有很好的多模谐振特性,说明ZnO压电薄膜很好地激发出了厚度方向的纵声波,可应用于体声波器件和声表面波器件中.另外采用间接的方法得到ZnO压电薄膜在870MHz时的介电常数约为5.24,介电损耗因子为1.07,进一步减小介电损耗因子,可以提高器件的Q值.     

Magnetic Transition in Nonmetal N- and F-Doping g-ZnO Monolayer with Different Concentrations

In this paper, the geometrical, electronic, and magnetic properties of nonmetal (N, F) atom doping g-ZnO monolayer supercell forming 6.25, 12.5, and 25% concentrations have been investigated comprehensively using the first-principles method. The structural optimization implies that N or F atom doping g-ZnO monolayer causes the structural distortion around the doping atoms. Doping g-ZnO monolayer with one N atom is FM semiconductor, and the total magnetic moment is 0.651 μ_B. The N–N-pair or two N–N-pair doping g-ZnO is AFM states. The total magnetic moments mainly originate from the spin polarization of the doping atom N, and the rest comes from the nearest Zn and O atoms. Doping g-ZnO with F atoms with the concentrations of 6.25, 12.5, and 25% all are nonmagnetic semiconductor. The F-doping can adjust energy band gap, which increases with the increase of F concentration.     

Strain-engineering of band gaps in piezoelectric boron nitride nanoribbons

Two-dimensional atomic sheets such as graphene and boron nitride monolayers represent a new class of nanostructured materials for a variety of applications. However, the intrinsic electronic structure of graphene and h-BN atomic sheets limits their direct application in electronic devices. By first-principles density functional theory calculations we demonstrate that band gap of zigzag BN nanoribbons can be significantly tuned under uniaxial tensile strain. The unexpected sensitivity of band gap results from reduced orbital hybridization upon elastic strain. Furthermore, sizable dipole moment and piezoelectric effect are found in these ribbons owing to structural asymmetry and hydrogen passivation. This will offer new opportunities to optimize two-dimensional nanoribbons for applications such as electronic, piezoelectric, photovoltaic, and opto-electronic devices.     

Piezoelectric properties in two-dimensional materials: Simulations and experiments

The piezoelectric effect, discovered in 1880 by Jacques and Pierre Curie, effectively allows to transduce signals from the mechanical domain to the electrical domain and vice versa. For this reason, piezoelectric devices are already ubiquitous, including, for instance, quartz oscillators, mechanical actuators with sub-atomic resolution and microbalances. However, the ability to synthesize two-dimensional (2D) materials may enable the fabrication of innovative devices with unprecedented performance. For instance, many materials which are not piezoelectric in their bulk form become piezoelectric when reduced to a single atomic layer; moreover, since all the atoms belong to the surface, piezoelectricity can be effectively engineered by proper surface modifications. As additional advantages, 2D materials are strong, flexible, easy to be co-integrated with conventional integrated circuits or micro-electromechanical systems and, in comparison with bulk or quasi-1D materials, easier to be simulated at the atomistic level. Here, we review the state of the art on 2D piezoelectricity, with reference to both computational predictions and experimental characterization. Because of their unique advantages, we believe 2D piezoelectric materials will substantially expand the applications of piezoelectricity.     

Simulation of piezoelectric devices by two- and three-dimensional finite elements

A method for the analysis of piezoelectric media based on finite-element calculations is presented in which the fundamental electroelastic equations governing piezoelectric media are solved numerically. The results obtained by this finite-element calculation scheme agree with theoretical and experimental data given in the literature. The method is applied to the vibrational analysis of piezoelectric sensors and actuators with arbitrary structure. Natural frequencies with related eigenmodes of those devices as well as their responses to various time-dependent mechanical or electrical excitations are computed. The theoretically calculated mode shapes of piezoelectric transducers and their electrical impedances agree quantitatively with interferometric and electric measurements. The simulations are used to optimize piezoelectric devices such as ultrasonic transducers for medical imaging. The method also provides deeper insight into the physical mechanisms of acoustic wave propagation in piezoelectric media.     

Optimal design of laminated piezocomposite energy harvesting devices considering stress constraints

Energy harvesting devices are smart structures capable of converting the mechanical energy (generally, in the form of vibrations) that would be wasted otherwise in the environment into usable electrical energy. Laminated piezoelectric plate and shell structures have been largely used in the design of these devices because of their large generation areas. The design of energy harvesting devices is complex, and they can be efficiently designed by using topology optimization methods (TOM). In this work, the design of laminated piezocomposite energy harvesting devices has been studied using TOM. The energy harvesting performance is improved by maximizing the effective electric power generated by the piezoelectric material, measured at a coupled electric resistor, when subjected to a harmonic excitation. However, harmonic vibrations generate mechanical stress distribution that, depending on the frequency and the amplitude of vibration, may lead to piezoceramic failure. This study advocates using a global stress constraint, which accounts for different failure criteria for different types of materials (isotropic, piezoelectric, and orthotropic). Thus, the electric power is maximized by optimally distributing piezoelectric material, by choosing its polarization sign, and by properly choosing the fiber angles of composite materials to satisfy the global stress constraint. In the TOM formulation, the Piezoelectric Material with Penalization and Polarization material model is applied to distribute piezoelectric material and to choose its polarization sign, and the Discrete Material Optimization method is applied to optimize the composite fiber orientation. The finite element method is adopted to model the structure with a piezoelectric multilayered shell element. Numerical examples are presented to illustrate the proposed methodology. Copyright © 2015 John Wiley & Sons, Ltd.     

Piezo and photoelectric coupled nanogenerator using CdSe quantum dots incorporated ZnO nanowires in ITO/ZnO NW/Si structure

We report the fabrication of ITO/n-ZnO NW/p-Si sandwiched structure and its photoelectric and piezoelectric conversion properties. This hybrid cell was designed to harvest simultaneously both solar and mechanical energies. ZnO nanowires used in the work were grown on p-type Si substrates employing seed mediated low-temperature aqueous solution method. The synthesized ZnO nanowires were characterized by XRD, SEM and EDX characterization for their structural and morphological evaluation. The as-grown ZnO nanowires showed good crystallinity with c-axis preferable orientation. Free ZnO nanowires and CdSe quantum dots were also incorporated with the vertically grown nanowires and their response in harvesting optical and mechanical energies were investigated. The piezoelectric and photoelectric coupled effects of a ZnO nanowire device in the simultaneous conversion of both optical and mechanical energies have been studied for the first time with the goal of designing piezoelectric and photoelectric hybrid nanogenerator. This presented ITO/n-ZnO NW/p-Si heterojunction architecture is envisaged as a potentially valuable candidate for the next generation energy harvesting devices. Graphene-coated ITO was also used and its response was studied.     

“Self-Matched” Tribo/Piezoelectric Nanogenerators Using Vapor-Induced Phase-Separated Poly(vinylidene fluoride) and Recombinant Spider Silk

Flexible biocompatible mechanical energy harvesters are drawing increasing interest because of their high energy-harvesting efficiency for powering wearable/implantable devices. Here, a type of “self-matched” tribo-piezoelectric nanogenerators composed of genetically engineered recombinant spider silk protein and piezoelectric poly(vinylidene fluoride) (PVDF)-decorated poly(ethylene terephthalate) (PET) layers is reported. The PET layer serves as a shared structure and electrification layer for both piezoelectric and triboelectric nanogenerators. Importantly, the PVDF generates a strong piezo-potential that modifies the surface potential of the PET layer to match the electron-transfer direction of the spider silk during triboelectrification. A “vapor-induced phase-separation” process is developed to enhance the piezoelectric performance in a facile and “green” roll-to-roll manufacturing fashion. The devices show exceptional output performance and energy transformation efficiency among currently existing energy harvesters of similar sizes and exhibit the potential for large-scale fabrication and various implantable/wearable applications.     

Simulations of piezoelectric Lamb wave delay lines using a finite element method

The method of piezoelectric finite elements was applied to the simulation of piezoelectric Lamb-wave delay lines with and without acoustical absorbers. In this finite-element analysis, free as well as electrically driven vibrations were computed. The shapes of the symmetric Lamb modes were determined by the solution of eigenproblems, and the transient mechanical build-up process was studied for a switched electrical sine wave excitation. The transfer function, the group delay time, and the impedance matrix of devices of different designs are calculated. The good agreement between simulation and experimental results indicates the suitability of the finite-element method for optimizing acoustic delay-line devices.     

BiAlO3掺杂PZT陶瓷的高压电性能和低电场应变滞后

铅基压电陶瓷因其优异的压电性能, 被广泛应用于压电器件。其中, 压电驱动器要求压电陶瓷具有较高压电性能并且在电场下具有较高的电致应变和较小的应变滞后。本研究通过施主-受主共掺, 得到高压电性能和低电场应变滞后的PZT陶瓷。采用传统固相反应法制备了(1-x)(Pb_0.95Sr_0.05)(Zr₅₃Ti₄₇)O₃-xBiAlO₃+0.2%MnO₂陶瓷(掺杂量为质量百分数), 并对其微观结构和压电性能进行了研究。结果表明：BiAlO₃掺杂量较少时, 陶瓷中缺陷偶极子的“钉扎”效应使得陶瓷畴壁转动困难, 陶瓷压电性能较弱, 应变滞后也较小。随BiAlO₃掺杂量增加, 缺陷偶极子“钉扎”效应减弱, 陶瓷的压电性能和应变滞后随之提高。本实验得到的性能最优组分为x=1.75%, 该组份陶瓷的压电系数d₃₃=504 pC/N, 机电耦合系数k_p=0.71, 机械品质因数Q_m=281, 居里温度T_C=312 ℃, 在10 kV/cm电场下的应变滞后仅为15%, 并且还具有较好的温度稳定性, 是一种具有应用价值的压电驱动器用压电陶瓷材料。     

Prediction of the T0 Shift between Specimens of Different Constraints Using the T-Stress Based T-Functions

Microcracking in piezoelectrics is found to produce two major effects on the effective piezoelectric properties: it weakens the electromechanical coupling and it changes its "directionality", i.e. the direction of mechanical (electrical) response to the applied electrical (mechanical) loads. The latter effect implies that microcracking in piezoelectric sensors and actuators reduces the accuracy of the devices. We quantify the mentioned loss of accuracy. This can also be viewed as a quantification of the "piezoelectric fatigue".