Out‐of‐Plane Polarization in Bent Graphene‐Like Zinc Oxide and Nanogenerator Applications

Highly efficient piezoelectric nanogenerator operation is demonstrated based on dynamic bending of graphene‐like ZnO nanosheets. Energy is harvested by an external resistor by virtue of a strong time‐varying piezoelectric polarization component perpendicular to the graphene‐like ZnO plane. It is shown analytically and verified numerically using molecular dynamics simulations that the $\overline{6}$m2 point group of flat graphene‐like ZnO is reduced to monoclinic m symmetry for bent graphene‐like ZnO. The latter symmetry allows for a nonzero and large piezoelectric polarization component perpendicular to the plane of the 2D structure. The numerical results confirm that flexoelectric effects are negligible subject to graphene‐like ZnO bending operation.     

半导体材料中自旋极化的光学注入与探测

综述了自旋电子学的一些新进展,重点介绍了自旋极化的光学注入、弛豫机制和光学探测等方面的内容,并涉及到与自旋有关的自旋霍尔效应(SHE)和纯自旋流等物理效应.     

Fatigue‐Resistant Bioinspired Graphene‐Based Nanocomposites

Graphene is an attractive building block for constructing functional materials of flexible electronic devices, due to its extraordinary mechanical and electrical properties. Up to now, large amounts of high‐performance graphene‐based nanocomposites are fabricated. However, the fatigue behavior of graphene‐based nanocomposites, a key parameter for flexible electronic devices, is rarely investigated. According to the fatigue mechanisms of thermosetting polymer composites, the fatigue resistance of graphene‐based nanocomposites can be significantly improved by effectively restricting the crack growth. Natural nacre demonstrates unique multisuppression of crack propagation, which is attributed to its sophisticated interfacial architecture over multiple length scales, resulting in remarkable fracture toughness. The crack suppression mechanisms corresponding to different interfacial design strategies within bioinspired graphene‐based nanocomposites (BGBNs) are summarized in this feature article. The static mechanical properties, electrical conductivity, and fatigue resistance of these BGBNs are compared and discussed. The synergistic effect from various interfacial interactions and building blocks is highlighted to serve as the guidance for constructing novel fatigue‐resistant BGBNs. The promising applications of fatigue‐resistant BGBNs in flexible electronic devices are reviewed, and several challenges and corresponding solutions are proposed. The perspective of fatigue‐resistant BGBNs for fundamental research and commercial application is depicted.     

Interface‐Assisted Sign Inversion of Magnetoresistance in Spin Valves Based on Novel Lanthanide Quinoline Molecules

Molecules are proposed to be an efficient medium to host spin‐polarized carriers, due to their weak spin relaxation mechanisms. While relatively long spin lifetimes are measured in molecular devices, the most promising route toward device functionalization is to use the chemical versatility of molecules to achieve a deterministic control and manipulation of the electron spin. Here, by combining magnetotransport experiments with element‐specific X‐ray absorption spectroscopy, this study shows the ability of molecules to modify spin‐dependent properties at the interface level via metal–molecule hybridization pathways. In particular, it is described how the formation of hybrid states determines the spin polarization at the relevant spin valve interfaces, allowing the control of macroscopic device parameters such as the sign and magnitude of the magnetoresistance. These results consolidate the application of the spinterface concept in a fully functional device platform.     

基于椭圆参数的最优接收极化

从极化的椭圆参数与极化球的Stokes参数的关系出发,直接推导出干扰环境下极化球面上的优化接收信号干扰噪声比参量表示式。该式对极化优化接收和信号增强很有用处。尽管难以得到全局最优解析解,但仍比较详细地给出了小圆和大圆轨道下的局部最优解,并进行了仿真。     

长波长垂直腔面发射激光器开关及双稳特性

为了研究垂直腔面发射激光器偏振转换特性,基于自旋反转模型,数值研究了正交光注入下1550nm垂直腔面发射激光器频率诱导偏振开关及双稳特性。结果表明,在正交光注入下,连续改变注入光与激光器光场内x线性极化模的频率失谐可诱导产生两类偏振开关和偏振双稳现象,且注入光强与偏振电流的变化都显著影响双稳宽度和激光器的输出特性;合理选择操作条件,可实现对1550nm垂直腔面发射激光器频率诱导偏振开关及双稳的控制。这一结果对垂直腔面发射激光器在全光开关和全光存储等领域的应用具有参考价值。     

Graphene‐Based Actuator with Integrated‐Sensing Function

Flexible actuators have important applications in artificial muscles, robotics, optical devices, and so on. However, most of the conventional actuators have only actuation function, lacking in real‐time sensing signal feedbacks. Here, to break the limitation and add functionality in conventional actuators, a graphene‐based actuator with integrated‐sensing function is reported, which avoids the dependence on image post‐processing for actuation detection and realizes real‐time measurement of the shape‐deformation amplitudes of the actuator. The actuator is able to show a large bending actuation (curvature of 1.1 cm^?1) based on a dual‐mode actuation mechanism when it is driven by near infrared light. Meanwhile, the relative resistance change of the actuator is ?17.5%. The sensing function is attributed to piezoresistivity and thermoresistivity of the reduced graphene oxide and paper composite. This actuator can be used as a strain sensor to monitor human motions. A smart gripper based on the actuators demonstrates perfect integration of the actuating and sensing functions, which can not only grasp and release an object, but also sense every actuation state of the actuator. The developed integrated‐sensing actuator is hopeful to open new application fields in soft robotics, artificial muscles, flexible wearable devices, and other integrated‐multifunctional devices.     

基于椭圆参数的最优极化策略

针对基于椭圆参数的干扰环境下极化球面上的优化接收信干噪比参量等式,分析了几种特殊情况下的解析解,提出了几种基于椭圆参数的极化优化策略,包括三步搜索比较策略TSSC。在仿真实验中,对多种优化策略进行了比较。结果表明,TSSC策略只需在三次局部最优计算后再进行比较就几乎达到了全局最优,并用蒙特.卡罗法作了验证。     

基于波长扫描调制法测量保偏光纤的偏振特性

分析了保偏光纤偏振特性及其拍长和偏振消光比的基本测量原理,并根据单模保偏光纤基模的2个正交偏振模分量HEx11与HEy11间的相位差与波长的关系,推导出偏振拍长的测量关系式,提出了测量保偏光纤偏振特性的波长扫描调制法.采用此方法对熊猫型保偏光纤(YOFC-3367WY)的偏振特性进行了验证性实验研究.拍长和偏振消光比的测量结果表明,在该保偏光纤工作波长处试验结果与理论分析相当一致,说明该方法具有简单易行、测量精度高的优点.     

Hybrid Interface States and Spin Polarization at Ferromagnetic Metal–Organic Heterojunctions: Interface Engineering for Efficient Spin Injection in Organic Spintronics

Ferromagnetic metal–organic semiconductor (FM‐OSC) hybrid interfaces have been shown to play an important role for spin injection in organic spintronics. Here, 11,11,12,12‐tetracyanonaptho‐2,6‐quinodimethane (TNAP) is introduced as an interfacial layer in Co‐OSCs heterojunctions with an aim to tune the spin injection. The Co/TNAP interface is investigated by use of X‐ray and ultraviolet photoelectron spectroscopy (XPS/UPS), near edge X‐ray absorption fine structure (NEXAFS) and X‐ray magnetic circular dichroism (XMCD). Hybrid interface states (HIS) are observed at Co/TNAP interfaces, resulting from chemical interactions between Co and TNAP. The energy level alignment at the Co/TNAP/OSCs interface is also obtained, and a reduction of the hole injection barrier is demonstrated. XMCD results confirm sizeable spin polarization at the Co/TNAP hybrid interface.     

基于极化椭圆参数的零导数正交搜索最优极化方法

针对基于极化椭圆参数的信干噪比参量等式,提出一种基于极化椭圆参数的零导数正交搜索极化优化方法并进行了详细的讨论.该方法首先沿着一条特殊的基线进行局部优化就基本接近全局最优点,接着进行两个正交方向上的零导数搜索,而且搜索过程中每一步都只需简单地利用前一步局部最优解的结果.经过大量试验,给出了参数范围.结果表明ZDOS方法是有效的,基本上只需几步计算后就找到了全局最优点.     

Space‐Charge‐Stabilized Ferroelectric Polarization in Self‐Oriented Croconic Acid Films

Great progress has been made recently in molecular ferroelectrics with properties even comparable to those of inorganic ferroelectrics. However, it is difficult to develop basic thin films and devices for practical applications since most molecular ferroelectrics are uniaxial. The single polar axes of crystallites inside their films, if available, are usually oriented randomly. These can induce the components without contribution to ferroelectric polarization and a large depolarization electric field to suppress polarization. In this work, it is demonstrated that uniaxial croconic acid films in two‐terminal devices, deposited by thermal evaporation, can show effective ferroelectric polarization and nonvolatile memory switching behavior with small coercive fields of 11–30 kV cm^?1. The polar c‐axes in thick crystalline films (>500 nm) are found to be self‐oriented nearly at a desired direction. With the assistance of trapped charges, stable ferroelectric polarization can be achieved, in spite of the existence of nonferroelectric components. These may pave a way to utilize uniaxial molecular ferroelectrics for various applications, such as gate dielectrics, electrets, and memory devices.     

Concentration Polarization of Salt‐Containing Liquid Electrolytes

Using the example of Li‐battery electrolytes, the importance of the concept of conservative ensembles for polarization behavior and transference measurements of salt‐containing liquid electrolytes is stressed. The conventional evaluation of the stationary values fails if the ion pair is mobile and can act as a vehicle of a single ion such as Li⁺. The necessary generalization is considered. While the analytical form of the time dependence of voltage or current is not affected provided the ion pairing is sufficiently fast, the diffusion coefficient contains nontrivial extra contributions. Finally, soggy‐sand electrolytes are inspected, in which polarization occurs in the space‐charge zones.     

基于微分进化的极化WSF信号参数估计算法

极化敏感阵列与传统的天线阵列相比,可以同时接收到信号的空间信息和更加完整的电磁信息,由于受信号极化变化的干扰较小,接收增益更高,估计出的极化状态参数可以用于检测、多址等领域,因此具有更加广阔的开发价值。极化加权信号子空间(WSF)算法的精度、分辨率明显优于一般子空间类算法,并且可以处理相干信号,鲁棒性较好,与传统空间谱WSF相比,需要估计的参数多了一倍,计算量问题显得更加突出。针对该问题,首先将遗传算法应用于联合谱WSF,与传统测向不同,性能不佳。微分进化算法简单,收敛速度快,搜索精度高,性能稳定,将该算法应用于极化加权信号子空间算法的多维函数求解,并将它与基于遗传算法的极化WSF进行比较,证明文中算法的有效性。     

硅基片上偏振分束器研究进展

硅基集成光波导具有很高的折射率对比度,能将光场限制在纳米尺度,是制备结构紧凑、高效的纳米光子器件的关键。但是,高折射率对比度也会引起波导双折射效应。因此,几乎所有纳米光子器件都是偏振相关的。偏振分束器是偏振分集光子集成电路中克服硅纳米器件强偏振依赖性的重要组成部分,在片上相干通信、传感与环境检测等领域具有广阔的应用前景。目前报道的基于亚波长光栅波导结构的偏振分束器,工作带宽在200 nm以上,消光比也超过了20 dB。文章简述了各种类型偏振分束器的工作原理,对其尺寸、消光比、带宽等方面的性能进行了比较,分析了各类偏振分束器的优劣势,最后总结了其主要应用场景并展望了未来发展方向。     

基于遗传算法极化雷达反干扰接收极化选择

在有效采用极化状态基础上,采用极化对消技术使接收天线与之极化正交,可以使雷达工作在相对于干扰失配状态,从而达到反干扰目的。基于遗传算法,给出了在雷达工作频带内存在多个不同频、非相干干扰源时,接收天线最佳极化选择方法。针对典型算例,与穷举法、拉格朗日乘子求解比较,在达到相同的求解精度前提下,遗传算法用时较少,操作简单,大大节省了计算资源。     

天线极化轨道的概念修正及物理内涵研究

雷达变极化技术是当前极化雷达发展的关键技术之一;而极化轨道在变极化技术中是个重要的概念,很多相关的应用研究也多以此概念为前提。针对目前圆型极化轨道概念的误区,从严格的数理推导出发,定义了γ、极化轨道,给出了更完善的极化轨道概念,扩充了其物理内涵,并指出了极化轨道约束的变极化器实现途径,为后续的目标局部最优极化、极化信号的优化接收以及目标散射能量最优化等提供了新的研究视角。     

A Corner‐Fed Microstrip Circular Antenna with Switchable Polarization

In this paper, a design for a novel microstrip antenna with circular polarization diversity is proposed and experimentally investigated. This antenna is excited by a microstrip line, which is located at the corner of a circular patch. The polarization state can be switched electrically by setting a diode to on or off. The novel structure we describe here enables the optimization of the input match for both polarizations. From the measured result, good axial ratios are observed at the operating frequencies.     

基于图像分类的极化SAR系统的极化误差分析

讨论了极化合成孔径雷达（SAR）系统的极化误差,从分类精度误差的角度分析了极化误差对以基于Wishart分布的最大似然法为分类器的图像分类的影响,并给出计算结果。实验结果表明,出于不影响图像分类的考虑,极化通道幅度失衡应限制在[-3 dB,3 dB]范围内,极化通道的相位失衡应控制在[-13°,13°],极化转换开关的极化隔离度应高于35 dB,天线的极化隔离度应高于30 dB。