垂直沉积法自组装胶体光子晶体的研究进展

光子晶体是一类电介质常数非均匀分布的人工材料,由于其折射率的非均匀分布对入射电磁波的调制会产生类似于半导体能带结构的光子带隙特性.自1987年提出光子晶体的概念以来,采用自组装方法制备胶体晶体已成为近年来的光子晶体领域的研究热点.基于垂直沉积的自组装方法因具有设备简单、经济,制备周期短, 晶体层厚可控等优点而受到日益广泛的重视.本文阐述了垂直沉积法自组装的机理、实验方法、缺陷控制、应用研究等方面的最新进展,并对垂直沉积法自组装光子晶体的发展趋势及前景作了介绍.     

垂直沉积法制备二氧化硅胶体晶体及其表征

利用垂直沉积法将单分散的二氧化硅胶体微球自组装生长为胶体晶体 ,并用扫描电子显微镜和紫外可见光分光光度计对其显微形貌和光学特性进行了表征 .结果表明二氧化硅微球有序堆积 ,自组装成胶体晶体 ,其结构为FCC密排结构 ,表面为FCC密排结构的 ( 1 1 1 )面 ;反射光谱还表明 ,所制备的胶体晶体的光子带隙位于可见光波段 .与重力沉淀等其他自组装方法相比 ,垂直沉积法制备胶体晶体具有能够用胶体微球粒径和胶体溶液浓度精确控制样品厚度等优点     

Effect of sintering on the optical properties of SiO2 colloidal crystal multilayers

High-quality SiO2 colloidal crystal multilayers were fabricated from ethanol solutions by the vertical deposition method and the effect of sintering on the optical properties of the samples was investigated. Optical properties,which are determined by the photonic band structure, weres tudied by means of light transmission and reflection measurements. The morphology of the samples was characterized by scanning electron microscopy (SEM). SEM images illustrate the ordered close package of the spherical colloids in planes parallel to the substrate surface. In addition, the sampie is crackless as a result of an appropriate drying rate. It is shown that with the increase of the sintering final temperature, though the depth and the width of the peak of Bragg diffraction of the sample vary vastly, the peak produces few blue shifts. Optical measurement results were compared favorably to the microstructural properties of the colloidal crystal multilayers.     

化学沉积法制备CdS纳米薄膜及成膜机理

分别以Cd(NO_{3)2和(NH2)2CS作为镉源和硫源, 用化学沉积法(CBD)在ITO玻璃上生长CdS半导体纳米薄膜. 考察了Cd^{２＋浓度、 沉积温度、 沉积时间和后处理温度对CdS成膜的影响. 紫外 可见吸收谱和原子力显微镜结果表明, 改变溶液浓度和后处理温度都能有效调节CdS的吸收带边, 得到均一致密的CdS纳米薄膜. 探讨了膜形成机理, 给出了成核过程模型, 进一步修正了传统成膜机制. 认为ITO玻璃基片表面活性位和晶核的形成是均一致密CdS纳米膜形成的关键. 晶核的形成是电学、 热学、 力学和化学等因素共同作用的结果.}}     

桩基模型试验应变测试方法比较

桩身应变测试是桩基承载性能研究中的一项重要内容,是竖向荷载作用下桩身应力、轴力、侧摩阻力等荷载传递规律分析的基础.基于室内模型试验,采用常规的电阻应变片与光纤布拉格光栅（FBG）两种应变测试方法,对两组单桩在竖向荷载作用下的桩身应变特性做了完整的测试.对比分析试验结果表明：光纤布拉格光栅测得的应变数据具有较高的精度和稳定性,可以绘制更符合客观实际的桩身轴力和桩侧摩阻力曲线.     

Fabrication of MgB_2 superconducting films by different methods

MgB2 superconducting films have been successfully fabricated on single crystal MgO(111) and c-AL2O3 substrates by different methods. The film deposited by pulsed laser deposition is c-axis oriented with zero resistance transition temperature of 38.4 K, while the other two films fabricated by chemical vapor deposition and electrophoresis are c-axis textured with the zero resistance transition temperature of 38 K and 39 K, respectively. Magnetization hysteresis measurements yield critical current density Jc of 107 A/cm2 at 15 K in zero field for the thin film and of 105 A/cm2 for the thick film. For the thin film deposited by chemical vapor deposition, the microwave surface resistance at 10 K is found to be as low as 100μΩ, which is comparable with that of a high-quality high-temperature superconducting thin film of YBCO.     

分光光度法测定钒酸钇晶体原料中的含钇量

在不同pH值下 ,通过液相法合成了钒酸钇晶体原料 .采用分光光度法测定了上述合成原料中的含钇量 .实验结果表明 ,pH =7.0时为原料合成的最佳酸碱度 ,原料中的含钇量可达 99.39% ,与理论值接近 .可作为优质YVO4 光学晶体的生长原料     

晶体双折射现象的直观实验演示器(平台)

为了能够直观地观察到晶体中的双折射现象,利用非光学级的天然晶体冰洲石中杂质对光的散射作用,设计、制做了晶体双折射现象的直观实验演示器（平台）．通过这种演示器,可以使学生直观地观察到晶体中o、e两光线的真实轨迹．与偏振实验平台结合,可测出两光线的马吕斯定律曲线,验证了从冰洲石晶体中出射的两光线为光矢量相互垂直的线偏振光．     

Epitaxial growth of Fe/Ag single crystal superlattices and their magnetic properties

Single crystal Fe/Ag(001) superlattices with various periodicities were fabricated using ultrahigh vacuum evaporation deposition. It was found that single crystal bcc Fe layers and single crystal fcc Ag layers can epitaxially grow on a single crystal Ag buffer layer alternately, which was deposited on NaCl single crystal chips by ion beam assisted deposition. The magnetic measurements of the superlattices reveal an oscillation coupling between ferromagnetism and antiferromagnetism as a function of the Ag layer thickness. The oscillation period, which is 1 nm (5 Ag layers), is in good agreement with the calculated values when the Ag thickness is greater than 1.5 nm. While the thickness of the Ag spacer layer decreases to 1 nm, the oscillation coupling varies from calculations, which can be attributed to the intermixing of the interlayers according to the annealing results.     

单分散PS微球的制备及其胶体晶体的组装

无皂乳液聚合法制备了不同尺寸单分散的PS微球,采用离心法和垂直沉降法将之组装成具有光子带隙的人工欧泊.采用扫描电子显微镜(SEM)和可见-紫外光度计对PS胶体晶体的形貌、结构和光学性能进行了观察测试.结果表明厚度较大的PS胶体晶体可以通过离心法组装制得,当转速为1 000 r/min、干燥温度为40℃时可以组装得到高质量的PS胶体晶体,而垂直沉降法则较适合组装薄型的胶体晶体.从样品的光学特性讨论了适合组装的乳液固含量,改变组装胶体晶体的PS微球粒径可以得到不同的光带隙波长.     

A colloidal model system with an interaction tunable from hard sphere to soft and dipolar

Monodisperse colloidal suspensions of micrometre-sized spheres are playing an increasingly important role as model systems to study, in real space, a variety of phenomena in condensed matter physics--such as glass transitions and crystal nucleation. But to date, no quantitative real-space studies have been performed on crystal melting, or have investigated systems with long-range repulsive potentials. Here we demonstrate a charge- and sterically stabilized colloidal suspension--poly(methyl methacrylate) spheres in a mixture of cycloheptyl (or cyclohexyl) bromide and decalin--where both the repulsive range and the anisotropy of the interparticle interaction potential can be controlled. This combination of two independent tuning parameters gives rise to a rich phase behaviour, with several unusual colloidal (liquid) crystalline phases, which we explore in real space by confocal microscopy. The softness of the interaction is tuned in this colloidal suspension by varying the solvent salt concentration; the anisotropic (dipolar) contribution to the interaction potential can be independently controlled with an external electric field ranging from a small perturbation to the point where it completely determines the phase behaviour. We also demonstrate that the electric field can be used as a pseudo-thermodynamic temperature switch to enable real-space studies of melting transitions. We expect studies of this colloidal model system to contribute to our understanding of, for example, electro- and magneto-rheological fluids.     

Suppression of crystal nucleation in polydisperse colloids due to increase of the surface free energy

The formation of small crystallites is governed by two competing factors: the free energy gained upon transferring constituent atoms, molecules or colloidal particles from the metastable liquid to the more stable solid, and the free energy needed to create the surface area of the crystallite. Because the ratio of surface area to bulk is large for small particles, small crystallites dissolve spontaneously under conditions where larger crystallites are stable and macroscopic crystal growth occurs only if spontaneously formed crystallites exceed a critical minimum size. On theoretical grounds, the probability of forming such critical crystal nuclei is expected to increase rapidly with supersaturation. However, experiments show that the rate of crystal nucleation in many systems goes through a maximum as the supersaturation is increased. It is commonly assumed that the nucleation rate peaks because, even though the probability of forming critical nuclei increases with increasing concentration, the rate of growth of such nuclei decreases. Here we report simulations of crystal nucleation in suspensions of colloidal spheres with varying size distributions that show that the probability that critical nuclei will form itself goes through a maximum as the supersaturation is increased. We find that this effect, which is strongest for systems with the broadest particle size distribution, results from an increase with supersaturation of the solid-liquid interfacial free energy. The magnitude of this effect suggests that vitrification at high supersaturations should yield colloidal glasses that are truly amorphous, rather than nano-crystalline.     

中频非平衡磁控溅射制备Ti-N-C膜

采用霍尔离子源辅助中频非平衡磁控溅射技术,通过改变工作气氛、偏压模式、溅射电流以及辅助离子束电流,在不锈钢材料基体上制备了Ti/TiN/Ti(C,N)硬质耐磨损膜层.对薄膜的颜色、晶体结构、膜基结合力等性能进行了检测分析.结果表明:膜层的颜色对工作气氛非常敏感,反应溅射中工作气氛的微小变化会引起表面膜层颜色很大的变化.在正常的反应气体进气量范围内和较小的基体偏压下,薄膜的晶体结构没有明显的择优取向.但是反应气体的过量通入会使薄膜的晶体结构出现晶面择优取向趋势.非平衡磁控溅射成膜技术对薄膜晶体结构的择优取向影响并不是很大.在镀膜过程中施加霍尔电流,可以有效地增加膜基结合力.     

氯化钾晶体声子谱的唯象计算

在合理的近似下,通过拟合实验弹性系数的唯象方法确定了氯化钾晶体的最近邻与次近邻力常数,进而求得其声子谱。计算时计入长程的库仑作用和多体修正,结果与实验符合良好。这种方法还可用于其它碱金属卤化物声子谱的计算。     

In situ observation of colloidal monolayer nucleation driven by an alternating electric field

The nucleation of crystalline materials is a hotly debated subject in the physical sciences. Despite the emergence of several theories in recent decades, much confusion still surrounds the dynamic processes of nucleation. This has been due in part to the limitations of existing experimental evidence. Charged colloidal suspensions have been used as experimental model systems for the study of crystal nucleation and structural phase transitions, as their crystallization phase diagram is analogous to that of atomic and molecular systems, but they can be visualized using microscopy. Previously, three-dimensional imaging of colloidal nucleation dynamics was achieved using confocal microscopy. However, the limited temporal resolution of the confocal microscope is of concern when trying to capture real-time colloidal crystal nucleation events. Moreover, as the thermodynamic driving force has remained undefined, data on key factors such as the critical nuclei size are at best semiquantitative. Here we present real-time direct imaging and quantitative measurements of the pre- and post-nucleation processes of colloidal spheres, and the kinetics of nucleation driven by an alternating electric field, under well-defined thermodynamic driving forces. Our imaging approach could facilitate the observation of other rarely observed phenomena, such as defect and grain-boundary formation and the effects of foreign particles during crystallization. Furthermore, it may prove useful in identifying optical and biological technologies based on colloids.     

掺杂Bis-MSB紫外激光染料的聚苯乙烯小球单分子层周期阵列形成的可见光衍射

光子晶体是近年来全世界的研究热点之一。文中探讨了在实验室中用自组装的方法制备聚苯乙烯小球二维胶体晶体的过程,并实验研究了He-Ne激光器发出的激光束聚焦到样品上所产生的可见光衍射图案。     

基于ARM的食品过敏原快速测试仪设计

设计了一种基于石英晶体微天平的便携式食品过敏原快速测试仪,其工作原理是抗体抗原电化学反应过程中,反应物积淀到电极而引起石英晶体振荡频率的改变,通过测量石英晶振的频移,并利用一定的数学模型实现半定量测定过敏原。该系统主要由独特的高频信号发生器、QCM传感器和信号采集处理器等部分组成,借助嵌入式计算机强大的数字信号处理功能,实现了在线实时快速测量,且具有较高的测量精度。此外,如换用其他生物传感器和相应的分析软件,也可用于有害气体、水质等的微检测。     

二季戊四醇和季戊四醇分离结晶动力学研究

从结晶粒径与晶核数密度关系，晶体生长速率与成核速率关系着手，研究了二季戊四醇和季戊四醇的结晶动力学特性。通过对两种不同物质结晶特征的分析，成功地从季戊四醇废渣中结晶分离二季戊四醇，一次结晶纯度达到90％以上。     

Preparation of modified SiO2 colloidal spheres with succinic acid and the assembly of colloidal crystals

SiO2 colloidal spheres were synthesized by St-ber method. In order to enhance surface charge of the SiO2 spheres, they were modified with succinic acid. Scanning electron microscope (SEM) shows that the average size of modified SiO2 spheres is 473 nm, and its distribution standard deviation is less than 5%; Fourier-transform infrared spectra (FT-IR) and X-ray photoelectron spectrometer (XPS) results indicate that one end of succinic acid is chemically bonded to the SiO2 spheres through esterification; Zeta potential of the modified SiO2 spheres in water solution is improved from -53.72 to -67.46 mV, and surface charge density of the modified SiO2 spheres is enhanced from 0.19 to 0.94 μC/cm2. SiO2 colloidal crystal was fabricated from aqueous colloidal solution by the vertical deposition method at 40℃ and 60% relative humidity. SEM images show that the sample of SiO2 colloidal crystal is face-centered cubic (fcc) structure with its (111) planes parallel to the substrate. Transmission measurement shows the existence of photonic band gap at 1047 nm.     

C_(2v)对称的d~4(d~6)电子组态哈密顿矩阵

本文未采用任何可调参量实验拟合的方法,直接得出含Trees改正在内的C_(2v)对称d~4(d~6)电子组态的哈密顿矩阵元。从理论上解决了计算凡具有这种性质离子的晶场吸收光谱,确又避免了结果的任意性。