阳极氧化铝模板表面结构化铁薄膜的磁光克尔效应

利用磁控溅射的办法在阳极氧化铝模板表面制备了结构化的铁薄膜,研究了其在660 nm波长s偏振光条件下的纵向克尔效应.这是一种获得磁光子晶体的简便方法.对比连续与结构化铁薄膜的克尔信号,可推测阳极氧化铝模板表面结构化铁膜中存在两相,而且这两相中的磁矩存在相互作用.当沉积铁薄膜的名义厚度为20 nm时,结构化铁薄膜的克尔信号和矫顽力信号都增强到最大.     

溶胶-凝胶法制备LaNiO3薄膜及其电学性能研究

采用溶胶-凝胶法在SiO2/Si衬底上制备了LaNiO3薄膜,并通过改变退火温度和薄膜厚度对其微结构和电学性能进行了表征测试.X射线衍射(XRD)和电阻率测试结果表明,随着退火温度和厚度的增加,LaNiO3薄膜的结晶质量明显提高,薄膜电阻率也逐渐下降.当退火温度为800℃时,厚度为630 nm的LaNiO3薄膜电阻率最小,达到了1.37 mQ·cm.此外,利用LaNiO3薄膜作为下电极制备的2; Nb-Pb(Zr06Ti0.4)O3薄膜呈良好的钙钛矿相结构,且经过1010铁电循环测试周期以后,2; Nb-Pb(Zr06Ti0.4)O3薄膜的铁电性能未出现明显下降,表明该LaNiO3薄膜是生长PNZT铁电薄膜的优良下电极材料.     

利用含吸收的纳米涂层实现的克尔效应增强

本文研究了含吸收的纳米涂层对铁薄膜的磁光克尔效应的影响.利用厚度仅为30 nm的吸收涂层硅实现了铁薄膜纵向和横向克尔效应的增强.660 nm波长处的纵向克尔转角的最大增强系数为1.46,对应涂层厚度为9nm,基于等效折射率模型,我们对纵向克尔转角进行了拟合,拟合结果可以很好的匹配实验.同时,铁薄膜的横向克尔效应也得到了增强,最大增强系数为9.43.     

RIG型磁光薄膜的研究进展及应用

随着光通信技术与光子集成电路的发展,非互易性器件作为光通信系统中重要的组成部分得到了越来越广泛的研究与应用。基于磁光效应制成的磁光隔离器和环行器是目前应用最为广泛的非互易性器件,为了将非互易性器件整块集成在硅片上,需制备性能与块状磁光材料相当的磁光薄膜。在近红外通信波段(1 550 nm),以钇铁石榴石(Y₃Fe₅O₁₂,YIG)为代表的稀土铁石榴石(RIG)具备优良的磁光效应,是最具应用前景的磁光材料之一。研究发现,使用稀土离子对YIG薄膜进行掺杂可以有效改善其磁光性能,尤其是Bi³⁺和Ce³⁺掺杂的YIG表现出巨法拉第效应。本文首先介绍了法拉第效应原理,介绍了三种常见磁光薄膜的生长方法,回顾了近年来的主要研究成果,介绍了磁光薄膜在光隔离器和环行器中的应用,最后对磁光薄膜的未来发展趋势进行了展望。     

无序化对有序铁铝金属间化合物磁性的影响

在平衡态时,化学计量比成份Fe3Al具有D03超结构,并表现出铁磁性,平均每个Fe原子的磁矩是1.7μB,而具有B2超结构的FeAl却是无磁的.利用快速凝固、冷加工处理、溅射和机械合金化等非平衡加工技术可以使D03-Fe3Al和B2-FeAl等有序铁铝金属间化合物相无序化.本文利用固体与分子经验电子理论(EET)和Jaccarino-Walker模型对铁铝金属间化合物的磁性进行了计算,研究了无序化对Fe-Al有序相磁性的影响.结果表明:完全无序的Fe75Al25和Fe50Al50,每个Fe原子的平均磁矩分别是2.01μB、1.41μB,铁铝金属间化合物的磁性可以通过无序化提高.     

铝/铁掺杂的非晶碳/铝结构的电致电阻效应研究

采用脉冲激光沉积方法在石英玻璃衬底上沉积铁掺杂的非晶碳膜(a-C:Fe),然后使用真空热蒸发设备在膜上镀铝(Al)电极层,形成Al/a-C:Fe/Al结构的器件.该器件在±5 V测试电压范围内显示出可逆电致电阻效应,具有较好的开关电压、开关比等参数,可用作电阻型随机存储器.     

PMN-PT单晶与Ag电极共烧界面结构及扩散行为研究

采用丝网印刷工艺在PMN-PT弛豫铁电单晶晶片表面涂覆了中温及高温两种银浆，通过快速烧结工艺分别在650和850℃条件下制备了银电极。采用扫描电子显微镜观察银电极表面及金属-晶体界面的微观结构，采用能谱分析了界面的元素分布情况。银电极厚度为几十微米，呈多孔结构，与晶体结合良好。经过烧结后，晶体中的Pb、Nb、Ti等原子向银电极发生了迁移，而高温银浆烧结后在界面形成几微米厚的过渡层，晶体中原子向电极中的迁移大幅度减少。不同晶向的PMN-PT晶片在高温下向银电极扩散过程中具有很强的晶面效应，[110]方向晶体中Pb、Nb、Ti原子向电极中的扩散程度小于[100]方向晶体。     

基于一阶反转曲线三维Ni反点阵列磁学特性研究

采用一阶反转曲线方法研究了三维Ni反点阵列中的磁偶极相互作用和磁化反转行为.以自组装聚苯乙烯球为胶体晶体模板,采用电化学沉积法制备出有序的三维Ni反点阵列.样品的孔径尺寸均为大约500 nm,厚度依次从0.3 μm到1.2μm.通过一阶反转曲线方法分析表明,随着样品厚度的增加,磁偶极相互作用减小,矫顽力分布变窄.这主要是由于随着厚度的增加,磁偶极相互作用向交换耦合作用转变的结果.     

弛豫铁电单晶的多功能特性及其器件应用

以Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃(PMN-PT或PMNT)为代表的弛豫铁电单晶具有远高于常用锆钛酸铅Pb(Zr_xTi_1-x)O₃(PZT)陶瓷的压电性能,引起了基于新一代压电单晶的功能器件研究热潮。本研究团队在国际上率先利用Bridgman方法生长出了大尺寸、高质量PMN-PT等弛豫铁电单晶(d₃₃～2 000 pC/N,k₃₃～92%),并对PMN-PT等弛豫铁电单晶的生长、多层次微观结构和性能调控进行了多方面的研究,发现弛豫铁电单晶不仅具有超高压电性能,还具有突出的热释电性能、电光性能以及与磁致伸缩材料复合形成磁电复合材料的超高磁电耦合性能。本研究团队多年来一直在努力推动弛豫铁电单晶在医用超声换能器、热释电红外探测器、电光器件、磁电型弱磁传感器等各种器件的应用研究。本文主要总结了弛豫铁电单晶的多功能特性,并介绍了本研究团队在弛豫铁电单晶器件应用上的研究结果。     

电极耦接变化对分子器件电子输运特性影响的研究

利用基于Green函数的 Tight-binding 理论,对phenalenyl构成的单分子器件电极耦接点变化情况下的电子输运特性进行了研究.通过理论计算,得出了分子与原子线电极间接点变化对电子输运的影响.结果显示电子通过phenalenyl分子器件的概率随着分子与电极的耦合点的变化而改变.当耦接点改变时,不仅电子通过phenalenyl分子的概率变化,而且无源正负能量开关器件的特征也发生变化.所得结果还揭示出在应用phenalenyl分子器件时,只需改变电极耦接,就可以获得具有不同电子学特性的分子器件.     

循环电场下钙钛矿铁电薄膜的极化疲劳机制

将循环电场引起电荷注入并产生局部相分解的理论引入到氧空位模型中,建立了一个解析形式的钙钛矿结构铁电薄膜极化疲劳模型.结合该模型讨论了铁电薄膜与金属电极间的低介电常数界面层对疲劳特性的影响,认为界面层对疲劳的产生起关键作用.运用该模型分析了不同松弛时间、电压、温度下的疲劳特性,并与已报道的实验结果进行了对比,模型计算结果与实验数据具有很好的一致性.     

Ferroelectric Liquid Crystals - Structure and Design

Interest in the synthesis of optically active smectic liquid crystals has increased considerably since the advent of a fast switching, bistable, electrooptic device configuration based on their ferroelectric properties. A number of structurally separate ferroelectric liquid crystal phases have been defined which possess differing properties. These types of phase can be utilized in different forms of application. The structures of the various ferroelectric smectic phases and the types of material which exhibit these modifications are discussed in detail. The design and engineering of materials to suit certain device criteria is related to the properties of the smectic ferroelectric phases. A relationship between the absolute spacial configuration of the optically active materials which exhibit ferroelectric smectic phases, the twist direction of the phase and the direction of the spontaneous polarization is developed.     

Lifshitz-Like Behaviour in Ferroelectric Liquid Crystals

In order to explain the anomalous behaviour of the critical magnetic field and the helical pitch in the vicinity of the Λ-line and the Lifshitz point in the ferroelectric liquid crystal DOBAMBC a model involving not only chiral but also non-chiral biquadratic coupling between the polarization and the tilt has been proposed. The model predicts an “S - like” dependence of the modulation wave vector close to the smectic C* - smectic A transition. High temperature resolution measurements of the helical pitch and the intensity of the diffraction sattelites indeed support the proposed model and seem to show that the pitch is finite at T_c. In such a case the Lifshitz field H_L is finite too.     

Physical Properties of Ferroelectric Liquid Crystals Incorporating a Boron Atom

Physical properties of a new type of ferroelectric liquid crystal incorporating a boron atom have been studied. Spontaneous polarization, tilt angle and chiral pitch of the new ferroelectric liquid crystals are compared with those of other types of ferroelectric liquid crystals. The alternation of the Ps direction and the twist sense is observed as the chiral center is moved further away from the core.     

Ferroelectric Liquid Crystals

A review of the ferroelectricity in liquid crystals is given, beginning with a discussion of the symmetry properties allowing a macroscopic polarization in some of the more ordered liquid crystal phases. The fundamental mechanisms behind the dipolar ordering are discussed in some detail. The two linear electric effects, ferro- and flexo-electricity, give rise to completely different phenomena. In the smectic C phase there is one ferroelectric coefficient and nine flexoelectric ones, giving independent contributions to the polarization of the medium. We further discuss helical and non-helical structures, doped and intrinsic infinite-pitch ferroelectrics and, finally, the rich potential of liquid crystal ferroelectrics aligned in the »book-shelfgeometry» for fast electro-optic devices.     

Polarization and Viscosity Measurements in a Ferroelectric Liquid Crystal by the Field Reversal Method

With the aim to develop a standard method for measurements of the polarization of ferroelectric chiral smectic C liquid crystalline materials, we have studied thin, well-aligned samples of MBRA-8 using the field-reversal method. The method also provides an estimate for the rotational viscosity and for the response times.     

Self-organization model for a cell system: Ferroelectric, ferroelastic, and magnetic states and related phase transitions

A model is proposed to explain the stability, phase state transformations, and coexistence of different phases for fungi cell ensembles (in particular, dimorphism and linear-to-spiral structure transitions with the Earth’s magnetic field screened). This model is based on (i) cell-connected soft polarization modes induced by charge compensation and related ferroelectric and ferroelastic phase transitions and (ii) intracell mobile orbit-spin-lattice clusters with competitive ferromagnetic-diamagnetic behavior and with orbitlattice and spin-lattice interactions. This model makes it possible to explain the structural and magnetic properties of the systems under consideration. In particular, the Lifshitz invariants in the free energy explain the formation of orbit-lattice and spin-lattice spiral and ring-type structures that are formed when the Earth’s magnetic field is effectively screened. The model proposed is not restricted to mitochondria, containing orbit-spin-lattice clusters based on the Fe³⁺/Fe²⁺ states (considered here).     

Fredericks Transition in Pure and Nanodoped Surface Stabilized Ferroelectric Liquid Crystals

Recently, ferroelectric liquid crystals (FLCs) doped with nanoparticles have attracted a wide interest not only from a scientific but also from a practical point of view and there is continuously growing interest in the effects caused by doping the ferroelectric nanoparticles. Furthermore, the presence of external fields exhibits a very interesting transition, reported by recent experiments. In this work, we investigate the response of a surface stabilized ferroelectric liquid crystal (SSFLC) doped with ferroelectric nanoparticles to an applied electric field. We assume that the smectic layers consist of uniform planes with a fixed orientation and the system is free from dislocation of constant layer thickness due to nanoparticles. We obtain the threshold field of orientational transition and the maximum deviation of the polarization vectors for a pure and a doped SSFLC medium. Then, we discuss the Fredericks transtion of the system and formation of inhomogeneous texture. It is found that the ferroelectric nanoparticles have significant influences in ordering behavior of a SSFLC medium and the threshold fields are critically changed by doping nanoparticles in the SSFLC, which is fundamental to operation of many liquid crystal devices.     

Dynamic Behaviour of Ferroelectric Liquid Crystalline Thin Layers in Electric Fields

The direction of the spontaneous polarization of a thin ferroelectric liquid crystalline film can be switched up and down between two stable states by applying an electric field. This process is investigated theoretically using the elastic continuum theory of liquid crystals. There are found two reorientation mechanisms with different switching rates. The regimes of fast bulk switching and relatively slow domain wall motion are separated by a critical threshold field.