Organic Magnetic Materials Studied by Positive Muons

Positive muons can be implanted into organic and molecular magnets in order to study their internal magnetic field distribution and any associated dynamics. The muon behaves essentially as a microscopic magnetometer, sensitive to local magnetic order and magnetic fluctuations. We describe some recent experiments using this technique which were performed on a variety of organic systems, including nitronyl nitroxide magnets and materials with spin-Peierls ground states, MEM(TCNQ)₂ and DEM(TCNQ)₂, and demonstrate how the technique can give information concerning their ground states.     

周期极化铌酸锂晶体电控光栅

提出周期极化铌酸锂晶体电控宽带光栅,并利用耦合波理论,推导出电控光栅的衍射光光强分布解析表达式。数值结果表明,该电控光栅的衍射光谱可被外加电场调控。在310 V的外加电压下,1.21~1.83 mm波段的1级光衍射效率达到60%以上,在1.5 mm的1级衍射光衍射效率为70%;而在165 V的外加电压下,0.68~0.92 mm波段的1级光衍射效率达到60%以上,在0.8 mm的1级衍射效率为81%。该电控光栅响应时间短,故有望在高速光开关、波分复用器或调制器方面有重要应用。     

电泵浦有机半导体激光器的关键技术

采用高品质因子低损耗的光学微腔结构研制了电泵浦脉冲方式工作的有机激光器件。增益介质为Alq₃ : DCJTI薄膜,透明导电IVO薄膜和Al薄膜分别作为阳极和阴极。面发射的激光从阴极侧发出,峰值波长为622 nm,阈值电流密度为860 mA/cm²。讨论了电泵浦有机微腔激光器研制过程中的关键技术。     

地面核磁共振反演导电层状模型

提出不同于常规线性规划的广义线性迭代反演成像技术,并将其应用于任意层状导电介质的地面核磁共振数据分析.在这种方法中,初始振幅强度的平方作为反演成像的对象,它可以表示为含水量分布的二次型形式,并且在反演成像迭代过程中,对应的Jacobian矩阵元素可以用解析形式显式表示出来.反演成像可以从均匀半空间模型开始迭代,理论上,2次迭代就可以完成成像过程.用实际数据对提出的反演成像理论进行了验证.与常规方法相比,新方法的成像结果与实际情况具有更好的一致性,证明了广义线性迭代反演成像不仅具有较好的稳定性和收敛性,还特别适合任意良导层状模型的地面核磁共振数据反演成像.     

胆甾相液晶电控螺旋畸变导致的布拉格反射特性

研究了平面织构胆甾相液晶在垂直于螺旋轴方向施加电场后,引起螺旋畸变导致布拉格反射光强度变化特性,利用液晶矩阵光学,琼斯矩阵法与Matlab矩阵计算软件对有螺旋畸变情况下的布拉格反射光谱特性进行了分析和数值计算.从数值计算和实验结果可知,胆甾相液晶在其垂直螺旋轴方向施加不同电压电场时,布拉格反射光中心波长不随电压改变,而布拉格反射光强会随电压的增大而减弱.提出一种电致螺旋畸变模型,对实验结果和数值计算结果给出了合理的解释,认为利用电场改变胆甾相液晶螺距进而设计电控颜色变化液晶器件的原理是不可靠的.     

Vortices in Low-Dimensional Magnetic Systems

Vortices are objects that are important to describe several physical phenomena. There are many examples of such objects in nature as in a large variety of physical situations like in fluid dynamics, superconductivity, magnetism, and biology. Historically, the interest in magnetic vortex-like excitations begun in the 1960s. That interest was mainly associated with an unusual phase-transition phenomenon in two-dimensional magnetic systems. More recently, direct experimental evidence for the existence of magnetic vortex states in nano-disks was found. The interest in such model was renewed due to the possibility of the use of magnetic nano-disks as bit elements in nano-scale memory devices. The goal of this study is to review some key points for the understanding of the vortex behavior and the progress that have been done in the study of vortices in low-dimensional magnetic systems.     

有机光电磁功能材料

有机光电磁功能材料是新一代材料。文章简要介绍了有机半导体、光导体、光致变色与电致变色材料、有机非线性光学材料、有机导体、超导体、导电高分子，以及有机铁磁材料和有机分子电子器件。     

连续变焦的聚合物分散液晶电控透镜

介绍了一种基于聚合物分散液晶材料的连续调焦电控透镜.在聚合物分散液晶盒的上表面电极上刻蚀圆孔,形成一个非对称电极,在液晶盒上下极板之间,诱发一个非均匀电场,从而引起聚合物分散液晶材料的折射率非均匀分布,形成电控变焦透镜.阐述了聚合物分散液晶可调焦透镜的基本原理,分析了透镜孔径对聚合物分散液晶透镜焦距的影响,在直径3mm和6mm的圆孔条件下,分别测量了透镜焦距随电压的变化关系.结果表明:电压从50V加到170V的过程中,透镜焦距逐渐减短,刻蚀3mm圆孔的聚合物分散液晶盒焦距从1.361 63m到0.429 21m,刻蚀6mm圆孔的聚合物分散液晶盒焦距从1.769 92m到0.548 43m.     

不同结构的电控双折射无刻痕光栅研究

用MLC-7700-100向列相液晶制备了不同结构的电控双折射无刻痕液晶光栅.用波长为632.8 nm的He-Ne激光为光源,测量两种液晶光栅的光学衍射特性,用偏光显微镜观察不同电压下两种液晶光栅的液晶分子偏转状态和织构态改变的情况,并进行分析对比.发现双面电极条纹液晶光栅的电控衍射特性比单面电极条纹液晶光栅好.此结果...     

有机电致磷光材料的研究新进展

综述了近几年来应用于有机电致发光二极管的有机电致磷光材料的研究新进展,重点回顾了三原色小分子电致磷光材料的研究进展.     

Polarization Spectral Hole-Burning in Organic Materials

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Ce 基重费米子材料的电子态研究与维度调控

重费米子材料作为一类典型的强关联电子体系,蕴含着非常规超导、奇异金属、量子临界、 磁有序、重电子态、关联拓扑态等新奇的量子态,而4f 电子在其中扮演着重要的作用。随着高分 辨角分辨光电子能谱和薄膜生长技术的发展,精确探测重费米子材料中4f 电子在能量/动量空间 的色散和谱权重成为了可能,这为从微观上理解这类材料中的电子关联效应和新奇量子现象提供 了重要的基础。本论文总结了几个典型的重费米子单晶和薄膜体系的电子态研究,包括Ce-115 体 系、CeCu2Si2、CeRh6Ge4 以及单晶 Ce 膜等。这些结果为理解重费米子体系中重电子态的形成 和温度演化、近藤杂化的能带/动量依赖、重电子能带与超导的关系、近藤效应与磁性和其它量子 态的竞争、4f 电子的维度调控等重要物理问题提供了谱学证据。     

Magnetic Nanoparticle Thermometry via Controlled Diffusion

The process of magnetic nanoparticle heating releases enormous amounts of thermal energy. Through typical calorimetric analyses, the total thermal energy released can be easily quantified; however, knowledge of nanoscale temperature is necessary. Herein, a novel method of nanoscale thermometry by analyzing intra-particle diffusion in core–shell nanoparticles is proposed. Heating the iron cores with an alternating magnetic field in a saline suspension encourages the diffusion of sodium ions into the silica shells of the particles, which is modeled numerically; however, experimental measurements are needed in order to provide accurate diffusivity estimations. After determining the diffusion characteristics from X-ray photoelectron spectroscopy) depth profiling of silica films, energy dispersive analysis with high-resolution transmission electron microscopy measures the sodium ion gradient within single particles before and after heating. When compared directly to the numerical simulations, the results indicate that the temperature gradient between particles and saline suspension reaches significantly higher temperatures than the macro-scale temperature of the solution. By accurately knowing the thermal gradient between nanoparticles and the surrounding medium, nanoparticles can be engineered to limit surface resistances as much as possible and promote high rates of thermal energy transfer.     

Grain Boundaries in Magnetic Nanostructured Systems

The nanostructured systems are characterized by a density of grain boundaries which is higher than that of microcrystalline systems, giving rise to unusual properties. Both the structural nature and the thickness of grain boundaries which are dependent on the synthesis conditions, strongly influence the total magnetic properties. We report several examples based on metallic and insulating nanostructured systems to illustrate how the presence of grain boundaries can be experimentally evidenced, as well as their structure and magnetic behavior, and finally the significant role of grain boundaries on the magnetic properties.     

Magnetization Reversal in Magnetic Bilayer Systems

Magnetization reversal in magnetic soft/hard bilayer systems is studied analytically by means of a variational method for magnetic energies in a continuum model. The demagnetization curve is involved with nonlinear equations,and the solution is given implicitly in the form of Jacobi functions,which is valid for the total reversal process. Based on the non-trivial solutions, hysteresis loops, as well as the maximum energy product(BH)_(max) versus thicknesses of soft/hard layers are obtained. With regard to(BH)_(max), improvement of the remanence competes with loss of coercive force. As a result, an optimum condition exists. For a given thickness of the hard layer, the optimum condition at which the largest(BH)_(max) could be achieved is discussed, which is slightly different from previous works.     

Magnetic Relaxation Coupling in Heterogeneous Systems

The effects of magnetization transfer hold considerable potential for providing new information in a magnetic resonance image. Recent applications and discussions, however, have neglected to utilize the full potential of the experiment by ignoring its sensitivity to tissue water content and to the nature of the macromolecular components. The magnetization-transfer experiment where one spin population is irradiated with a preparation pulse and its effects are detected in the solvent resonance is examined in the context of the simplified equations of Grad and Bryant. Specific effects on the magnetic relaxation properties of the solids and on the water content are examined. Recent developments in modeling such systems are discussed, and it is demonstrated that reports of magnetization-transfer rates may be underestimated in some cases. Complications of mobility within the solid macromolecular phase of the system are also addressed in the context of the currently employed model that assumes heterogeneous systems may be partitioned into two or more motionally distinct proton populations.     

有机电致发光材料与器件

简要介绍了有机电致发光器件的结构、电致发光机理、可用作电致发光材料的种类以及存在的一些问题，简述了电致发光材料及器件的研究现状及对未来的展望。     

Organic Materials for Optical Technologies

Photophysical processes in pyrane substitutes excited by high-power laser radiation are investigated. It is demonstrated that the examined molecules offer promise as active media of tunable lasers (including solid-state lasers), optical radiation limiters with = 532 nm, and emitting layers of organic light diodes.     

有机发光材料中的三重激发态

有机发光材料有望广泛应用于新一代柔性光电子器件。由于自旋多重性,有机分子发光材料 中单重激发态和三重激发态转换较慢,限制有机发光器件特别是电注入荧光器件的效率。我们介绍 下近年来通过分子设计操控激发不同时间尺度三重态的动力学来突破这一限制的策略,通过控制激 发单重态和激发三线态之间的电子耦合,利用热激子系间窜越、反向系间窜越、激发三重态稳定化 等过程能够有效提高有机发光材料的发光效率。在此基础上实现的热活化延迟荧光、有机长余辉发 光等在有机发光二极管、传感器、生物成像等领域有重要潜在应用价值。