纳米粒子形貌与表面等离子体激元关系

通过调控纳米粒子表面形貌,研究了纳米粒子形貌与表面等离子体激元之间的关系.采用水相化学合成法制备出粗糙表面"花朵"形银纳米粒子.通过自组装形成单层阵列,并进一步组装成复合结构超材料.测试了其光学行为,并将实验结果与树枝形纳米粒子、光滑表面纳米粒子进行对比分析.结果表明:光滑表面纳米粒子不能出现超材料效应,当粗糙程度增加...     

柔性基底红外波段左手材料制备及光学特性

采用平板电极化学电沉积的方法,通过调节实验参量,在柔性ITO导电薄膜基底上制备了尺度与红外波长匹配、结构单元大小不等、排列无序的银树枝状结构.通过调节聚乙二醇-20000浓度可以很好地调控银树枝状结构单元的形貌和尺寸,研究发现,在一定范围内增加电解液中的聚乙二醇-20000浓度,可在基底上形成分布较密、分枝较细、分枝级数较高的银树枝状结构单元.通过在银树枝状结构表面涂覆一定厚度的聚乙烯醇作为绝缘层,组装成了柔性“三明治”结构复合材料,测试得到样品在红外波段的多通带透射谱,平板聚焦实验进一步验证了样品的左手效应.     

纳米银组装结构的表面增强荧光效应

采用表面自组装技术,在玻片表面构筑银纳米粒子二维组装结构.银纳米粒子组装结构的吸收光谱表明银粒子表面等离子体共振与粒子间电磁偶合密切相关,偶极子表面等离子体共振更为敏感而发生较大位移.在银纳米粒子组装结构上,荧光素分子的荧光得到极大增强,其表面增强效应强烈依赖于组装金属粒子的表面等离子体共振.     

纳米Ag材料表面等离子体激元引起的表面增强拉曼散射光谱研究

用热蒸发的方法制备了纳米Ag材料,并用扫描电子显微镜对纳米粒子进行了形貌的表征,通过紫外—可见分光光度计得到Ag纳米粒子的透过谱,得到了Ag纳米粒子的表面等离子体共振的峰值位置.以罗丹明6G为探针分子测定Ag纳米粒子衬底的表面增强拉曼散射效应,通过拉曼散射光谱与透过谱研究了由表面等离子体激元的强极化场引起的表面增强拉曼散射效应,结合透过谱与拉曼增益因子提出了一种描述表面等离子体光学和电学特性的方法,并结合扫描电镜的结果给出了不同结构的纳米Ag材料对表面等离子体激元强度的影响. 关键词： 热蒸发 纳米Ag材料 表面等离子体 表面增强拉曼散射     

基于V形纳米天线的平面透镜设计与制备

传统透镜由于其体积大、性能差等因素的制约,使其在微纳光学系统中的应用遇到挑战。金属纳米结构能够耦合自由光波产生表面等离子体激元,通过控制表面等离子体激元来实现对入射光波的调控。V形等离子体纳米天线凭借其双共振效应以及0~2π的全相位调谐范围,使其在可以实现光束调控的金属纳米结构中脱颖而出。首先基于V形纳米天线设计了可以在34μm处高效聚焦的超透镜;接着利用聚焦电子束和光刻工艺制备样品;最后对样品进行表征分析与光学检测。这些工作将促进V形纳米天线在激光直写、光学集成方面的应用。     

径向偏振光下的长焦、紧聚焦表面等离子体激元透镜

表面等离子体激元透镜(plasmonic lens, PL)是一种通过激发和操控表面等离子体激元 (SPPs), 突破衍射极限, 实现亚波长紧聚焦的纳米光子器件. 如何实现高效率的紧聚焦及调控, 一直是研究PL的重点. 如果选取电矢量沿径向振动的径向偏振光作为PL的入射光, 可从各个方向激发SPPs, 提高紧聚焦的能量效率. 本文提出了一种在径向偏振光激发下的长焦深、长焦距、亚波长紧聚焦的表面等离子体激元透镜, 该透镜由中心T 形微孔、阶梯形同心环和同心环结构组成. 本文首先利用有限元方法数值分析了中心微孔-同心环结构透镜的聚焦特性, 结果显示径向偏振光由底部入射可高效激发SPPs, 并且中心微孔透射光与散射至自由空间的SPPs由于多光束干涉形成了紧聚焦. 为进一步压缩焦斑、增加焦距、加深焦深、改善透镜聚焦特性, 本文引入中心T形微孔-阶梯形同心环结构, 从而对阶梯表面的SPPs同时提供了相位调制和传播方向的控制. 经过参数优化, 该透镜结构实现了光斑焦深、半高宽、焦距分别是入射光波长的2.5倍、0.388 倍、3.22倍的亚波长紧聚焦; 而且该透镜具有结构紧凑、尺寸小、易于集成的优点, 满足了纳米光子学对于器件微型化和高度集成化的要求. 该研究结果在纳米光子集成、近场光学成像与探测、纳米光刻等相关领域具有潜在的应用价值.     

光诱导转化法制备片状三角形银纳米粒子的表面增强喇曼散射

采用柠檬酸三钠化学还原法制备球形Ag纳米粒子溶胶,并用高压球形氙灯对球形Ag纳米粒子溶胶进行光诱导实验.利用透射电子显微镜、紫外-可见吸收光谱研究了不同光照时间下的银胶纳米粒子的光谱特性和表面形貌,并以结晶紫为探针分子测量了银胶纳米粒子的表面增强喇曼散射光谱.实验结果表明:随着光照时间的增多,Ag纳米粒子溶胶颜色变化显著;紫外-可见吸收光谱吸收峰从单一峰渐渐显示出多个峰;透射电子显微镜图显示Ag纳米粒子由球形逐渐转变成片状三角形银纳米粒子、截角的片状三角形银纳米粒子;表面增强喇曼散射的增强效应随着光照时间的变化先逐渐增大,然后逐渐减小.     

玻璃基底上不规则银纳米结构的生长及其光学性质的研究

以经过硅烷化后玻璃片为基底,之后吸附金纳米种子,采用柠檬酸钠为还原剂,在荧光灯照射条件下还原硝酸银,制备出基底表面具有银纳米粒子聚集结构的材料。采用透射电镜、扫描电镜和紫外可见分光光度计对产物的形貌和性质进行了表征,并考察银纳米粒子的形貌对其薄膜基底SERS活性的影响。结果表明：随着光照时间增加至16 h,金种子长大为平均粒径110 nm的不规则状多晶银纳米粒子,且出现双层粒子堆积。基底上纳米粒子的吸收光谱上出现了由银粒子的表面等离子体激元偶极子耦合引发的强烈吸收峰：随着光照时间的变化,耦合峰在600～813 nm波段内移动。光照时间为12 h后得到的SERS活性基底具有最强的SERS信号。     

基于DNA自组装的金属纳米结构制备及相关纳米光子学研究

纳米光子学是研究光在纳米尺度下的行为以及光和纳米材料相互作用的一门科学.金属纳米材料凭借其独特的表面等离子体效应,可以在衍射极限以下对光进行传递和聚焦,因而是纳米光子学研究的重点.大量研究表明,通过调控金属纳米材料的形貌和成分可以控制表面等离子体的性质,从而对光进行可控调节.近年来,随着DNA纳米技术的发展,又为纳米光子学的发展带来了新的机遇.首先,人们发现不同的DNA序列可以调控金属纳米颗粒的成长,从而影响金属纳米颗粒的形貌和成分.此外,利用DNA自组装技术,可以将金属纳米颗粒组装成为有序可控的纳米结构.因此,基于DNA的纳米光子学研究近年来发展十分迅速.在此背景下,本文对相关研究进行归纳与总结,以期吸引更多研究人员的关注,推动该领域的进一步发展.本文首先介绍了金属纳米结构基于表面等离体实现突破光学衍射极限的原理,然后按照DNA对金属纳米结构的形貌或成分影响方式的不同分成若干部分,对基于DNA的纳米光子学做了系统的综述,最后展望了未来可能的发展方向.     

两种纳米粒子的自组装及表面增强拉曼光谱研究

在氨基硅烷化的单晶硅片表面通过静电自组装技术组装上金和金核铂壳两种纳米粒子,通过改变基底浸泡在溶胶中的时间控制基底上纳米粒子的密度。用扫描电子显微镜(SEM)对基底表面上的形貌进行表征,结果表明纳米粒子呈亚单层二维阵列分布。以吡啶(Py)为探针分子,用波长为632.8 nm的激发光作为激发光源,研究纯金和金铂复合基底上的表面增强拉曼光谱(SERS)行为。数据显示在金纳米粒子之间引入金核铂壳纳米粒子后,Py的两个特征峰的频率没有明显变化,但谱峰的强度却变弱了,其SERS信号衰减最大可至原来的24%。这是由于引入的铂的d态电子使金的等离子体激发猝灭,从而破坏了电磁场增强,使金的SERS信号衰减。     

自适应分层采样辅助粒子滤波在视频跟踪中的应用研究

以视频目标跟踪中粒子滤波的粒子采样优化设计为研究内容,提出一种自适应分层采样辅助粒子滤波算法,以实现保证跟踪准确度和兼顾跟踪鲁棒性的要求.以Bhattacharyya系数为参量设计了粒子数调节函数,能够根据跟踪质量在粒子集中自适应分配用于保证准确度的粒子数和维持鲁棒性的粒子数.以最小二乘法对目标运动的预测点作为产生新粒子集的均值偏移操作起点,使新粒子集更准确的描述目标似然分布并提高算法效率.不同场景下的跟踪实验表明,算法能很好的应用于遮挡和运动方向渐变等情况下的跟踪,处理时间满足实时性要求.     

The mechanics of particle accumulation structures in thermocapillary flows

The motion of small particles suspended in a cylindrical thermocapillary liquid bridge is considered. Owing to geometry and surface stresses the streamlines gather near the cylindrical free surface and provoke particle–free-surface collisions. We show numerically that tracers which are perfect but of finite size can accumulate on closed trajectories. A simple model is proposed to explain the attraction of particles to the closed trajectory based on the flow topology in the vicinity of a closed streamline which comes sufficiently close to the free surface and on particle–free-surface collisions which transfer particles among different streamlines.     

Simplistic surface active agents mediated morphological tweaking of CdS thin films for photoelectrochemical solar cell performance

This study reports on the formation of cadmium sulfide (CdS) nanostructures with controlled morphology synthesized via a simple chemical route in surface active agent environment. The effect of organic surface active agents (surfactants) as sodium dodecyl sulfate (SDS), polyethylene glycol (PEG) and cetyltrimethylammonium bromide (CTAB) on structural, morphological, optical and photoelectrochemical properties of CdS thin films have been studied. Our results reveal that the organic surfactants play key roles in tweaking the surface morphology. A compact spongy ball like morphology was observed for the CdS samples grown without organic surfactants. The cauliflower's with nanopetals from the CTAB, whereas crowded star fish like morphology is observed in PEG-mediated growth. Water hyacinth like morphology is tweaked using SDS. Considering the importance of these nanostructures, the growth mechanism has been discussed in details. Additionally, the samples are photoelectrochemically (PEC) active and having a compact surface with a nanoporous structure twig helps in improved photoelectrochemical performance compared to that of CdS deposits from surfactant free solution. This is a simplistic way to tune the morphology using surfactants, which can be applied to other energy conversion applications.     

Morphology of supported silver nanoparticles characterized by?optical and thermal desorption spectroscopy

Silver nanoparticles grown on a quartz substrate are investigated with optical and thermal desorption spectroscopy (TDS). Detailed information on the nanoparticle morphology is gained with new methods of data analysis. First, fitting the extinction spectra, using a comprehensive model, allows an estimation of the effective particle–particle distance. Second, the total surface area of the particles is determined with TDS of xenon. Third, the dependence of the plasmon resonance position on the amount of adsorbed xenon or benzene is used as a measure of the average particle size. The results for these three parameters, which are critical for potential applications of nanoparticle arrays, are shown to be mutually consistent. The methods demonstrated here are complementary to scanning probe techniques which characterize the particle morphology on a microscopic length scale.     

Morphology of Nanostructured Films for Environmental Applications: Simulation of Simultaneous Sintering and Growth

A sequential Brownian dynamics approach was used to establish the morphological evolution of a nanostructured particle deposit accounting for random diffusion, particle–particle and particle–surface interactions through van der Waals forces, and sintering of deposited particles. Monodisperse (30nm radius) titanium dioxide particles were used in the simulations. A linear sintering law rate expression was used to account for the decrease in total surface area of the deposit. Characteristics such as packing thickness, total surface area, and fractal dimension are reported as a function of time during the deposition process. Sintering resulted in higher fractal dimensions (as defined) for the deposits, and elevated temperatures resulted in more compact deposits.     

Surface modification and submicron structure of carbon fibers through high current pulse

This paper investigated the behavior of carbon fibers subjected to a ∼20 kA, ∼5 μs high current pulse. It was found that the broken fibers and submicron particles were generated by electrical explosion process. After high current pulsed discharge, the fiber diameter increased significantly, from 5-7 μm to ∼13 μm. Also, the surface rupture of carbon fibers with valleys of hundreds of nanometers was observed. Most notably, the submicron particles appeared with two typical shapes (near-sphere and square). The high current pulsed discharge of carbon fibers can be divided into three stages, namely, heating stage, phase change stage, and explosion stage. Indeed, the electrical explosion process occurred in the last stage of ∼200 ns. The nature behind these results is closely related to the plasma development during the explosion process. The plasma expansion due to a large plasma thermal stress leads to the incomplete explosion. In the explosion stage, the current passing through the fibers exhibited a huge fluctuation, indicating plasma instabilities. Finally, the physical mechanisms, how to affect the surface morphology of carbon fibers, are presented.     

Surface morphological changes induced in catalysts by acoustic waves

An interdigital transducer device equipped with a metal catalyst sample that can be used to enhance catalytic activity by acoustic excitation is investigated. It was found that the propagation of 20 MHz surface acoustic waves of the Rayleigh type on Pt thin film single crystals causes drastic changes in surface morphology. The process of film breaking is observed and it is concluded that a phase shift in the acoustic wave induced by folds and cavities in the sample is responsible for the appearance of cracks. The influence of the change in morphology on catalytic activity and the acoustically induced rate enhancement effect is studied, and it is concluded that these changes are not a significant factor in the observed enhancement.     

Selective laser processing of ink-jet printed nano-scaled tin-clad copper particles

The deposition of tin-clad nano-size copper particles was carried out by means of ink-jet printing. Curing the particles on Polyimide (PI) turned them into soldered structures using an Nd-YAG laser. Area coverage of 55% was achieved for a single-layer print. Subsequent laser sintering increased this value to 95%. A Butanol-based copper ink and an aqueous tin (Sn)-clad Copper (Cu) ink were produced and were ink-jetted in this work. These nano-metallic inks showed excellent suspension stability with particle weight concentrations as high as 5%. The ink components were examined by measuring the particle size distribution in a dispersed condition, and the melting temperature. A piezo ink-jet print head was used to deposit the inks onto a moveable substrate. The thermal effect of the laser irradiation allowed approaching and connecting adjacent particles by melting the particle’s tin coating. The results were examined with regard to structure and soldering properties using EDX, SEM and optical microscopy.     

Surface morphological changes and magnetic properties of Sc-substituted Y3Fe5O12 epitaxial films deposited on the GGG substrate

Sc-doped YIG films were grown on (1 1 1) oriented GGG crystalline substrate with disorientation angle within the range 0-25′. Sc³⁺ ion substitution was varied within the range 0.25-0.3 per formula unit. The films demonstrate different types of surface morphology versus film growth rate and substrate disorientation. Conditions for existence of these types of the surface morphology were defined. The field dependence of magnetic susceptibility at magnetization reversal in film plane and Faraday rotation at wavelength 633 nm for a magnetic field applied in perpendicular direction were measured to characterize the films grown. Films with “mirror-like” surface demonstrate a planar magnetization at room temperature.