单芯帽纳米颗粒的光学性质

基于三维时域有限差分法,计算了非球对称单芯帽纳米颗粒在不同结构参数作用下的局域表面等离子体共振(LSPR)响应。采用模板法和真空蒸镀技术制备了SiO_2@Au芯帽结构纳米颗粒,通过透射电子显微镜和紫外可见近红外分光光度计对其形貌和光学性质进行了测量分析,获得了金壳厚度、芯壳比、芯径和金属表面覆盖率等纳米结构参数对LSPR峰值吸收波长和吸收截面的影响规律。结果表明,芯帽纳米颗粒结构参数的微小改变会导致LSPR峰在可见光到近红外波段的宽带红移。     

金纳米空心半球壳膜的可调谐光学性质研究

以单层聚苯乙烯微球阵列为模板,通过控制其表面金膜蒸镀时间,制备了具有不同厚度的空心半球壳结构的金纳米膜.利用扫描电子显微镜和自制光谱仪分别测量了金膜表面形貌和其透射光谱,并分析了金膜形貌与其光学性质间的关系,同时以4-巯基苯胺为探针分子测定了金膜的表面增强喇曼散射效应.结果表明,该金纳米膜的表面等离子体共振波长随膜厚度增大而发生红移,在可见与近红外波段较宽范围内可调谐,并且,当金膜共振波长与入射激发光波长较近时,探针分子可产生出较强的表面增强喇曼信号.同时,对该现象的产生机制也进行了理论解释.     

有序金纳米颗粒阵列的制备及光吸收特性研究

采用纳米球刻蚀技术中漂移法在玻璃基片上制备较大 面积不同直径的聚苯乙烯小球掩模板, 采用磁控溅射技术在掩模板上沉积不同厚度的金薄膜, 去除聚苯乙烯小球后, 通过扫描电子显微镜观察到周期排列的三角状金纳米颗粒点阵. 通过紫外-可见分光光度计测试所制备样品的光吸收特性, 发现表面等离子体共振峰随粒径增大发生红移, 随金纳米颗粒高度增加发生蓝移. 基于Mie理论, 利用Matlab软件编程对不同粒径的金阵列光吸收特性进行理论模拟, 并与实验结果进行对比. 关键词： 纳米球刻蚀 金纳米颗粒阵列 表面等离子体共振     

银纳米粒子阵列的自组装及其表面增强拉曼光谱应用

在以聚赖氨酸为表面耦联层分子的玻片基底制备了银纳米粒子阵列。ＳＥＭ表征结果表明,银粒子以亚单层的形式排列在基底表面。比较银溶胶和纳米粒子阵列的紫外可见光谱可见聚赖氨酸耦联层对银纳米粒子的粒径具有一定的选择性,甲基紫精在银纳米粒子阵列上的表面增强ＦＴ拉曼光谱表明在近红外区拉曼散射的表面增强主要来自于化学增强效应。     

SiO_2/Ag核壳结构纳米粒子的制备及其表面荧光增强

以罗丹明B掺杂的SiO2球为核,通过化学还原的方法制备了二氧化硅/银核壳结构复合纳米粒子。采用透射电镜(TEM)、紫外-可见-近红外(UV-Vis-NIR)分光光度计和荧光分光光度计对二氧化硅/银核壳结构纳米粒子的表面形貌、表面等离子共振和表面荧光增强特性进行了研究和表征。结果表明,二氧化硅/银核壳结构纳米粒子的表面等离子共振峰具有明显的可调谐性,且其表面荧光增强强烈依赖于银壳层的表面等离子共振,随银壳层厚度的增大而增强。     

基于Ag纳米棒阵列的表面等离激元微型偏振器

采用静电近似理论计算了Ag纳米棒阵列在不同偏振光入射下的消光光谱。当入射光偏振方向平行于纳米棒长轴时会激发表面等离激元纵向振动模式,而当入射光偏振方向垂直于纳米棒长轴时会激发表面等离激元横向振动模式。基于两种模式共振波长的不同,采用Ag纳米棒阵列可以用来设计高性能的表面等离激元微型偏振器。Ag纳米棒阵列的偏振性能在纵向共振波长明显优于在横向共振波长,通过调节纳米棒的纵横比可以对纵向模式的共振峰位进行大范围调控。结果表明这种微型偏振器所适用的波长能够通过纳米棒的纵横比在可见到近红外波段范围内调控,而消光比和插入损耗能够通过纳米棒的直径和长度实现调控。     

氯离子对银胶的宽波段光吸收光谱的影响

本文借助紫外-可见-近红外吸收光谱、透射电子显微镜技术,研究灰银胶中加入氯离子后此体系的宽波段吸收光谱的变化,旨在探索氯离子对纳米银颗粒表面特性的影响。实验结果表明,氯离子的加入会引起胶体中银颗粒的凝聚和银纳米颗粒的聚集体形态的变化,造成银颗粒的本征吸收光谱的"蓝移"和近红外区新吸收带的出现。最后我们初步分析了此现象产生的机制。     

非对称银纳米双环表面等离激元光谱特性

贵金属纳米材料在入射光激发下能够产生表面等离激元,即金属表面自由电子产生集体振荡。当其振荡频率与入射光频率相同时,发生表面等离激元共振,形成一种特殊的电磁场模式和光谱特性。利用该电磁场模式和光谱特性, 能够调节金属纳米材料的光谱学行为,例如通过改变金属纳米结构的大小、形状以及周围介质介电常数等参数, 在微纳尺度上实现光谱学信号的有效调控。目前,除了具有一定对称性的贵金属纳米材料被大量研究和应用外,非对称纳米结构的表面等离激元光谱特性也受到广泛关注。研究表明,在可见-近红外波段光谱范围内设计表面等离激元光电传感器件的关键问题在于,如何有效地调节其消光谱的共振波长、半峰宽以及峰值强度等主要特征参数。提出一种基于银纳米双环组成的非对称结构,利用时域有限差分方法,在可见-近红外波段内,通过分别改变银纳米双环的尺寸、间距及入射光偏振方向等参数,计算了该纳米结构在不同条件下的消光谱。结果表明,在0.4～3 μm的消光谱内,入射光能够激发产生两个独立的表面等离激元共振峰。通过研究峰值波长处的电场分布图发现,上述共振峰分别对应两种不同的电磁场模式。结果还表明,消光谱内两个独立的共振峰可以通过改变该双环结构的不同参数,被分别地进行调节。其中,可以通过改变该双环结构的半径来有效调节短波长峰的共振波长和半峰宽,同时保持长波长峰的共振波长和半峰宽基本不变。此外,通过改变两环间距或入射光偏振方向,可以分别以不同趋势来调节两个共振峰的峰值强度。在提出的非对称银纳米双环的消光谱中,获得了能够被分别调节的两个表面等离激元共振峰,研究结果能够为可见-近红外波段内基于银纳米材料光电传感器件的开发设计提供理论基础。     

纳米银颗粒掺杂铋酸盐玻璃的光谱与三阶非线性光学特性研究

采用新型的热化学还原法,制备了银纳米颗粒掺杂的铋酸盐复合玻璃材料。利用紫外-可见吸收光谱观察到了银纳米颗粒表面等离子谐振(SPR)吸收的峰值位移特性,用拉曼光谱表征了引入银纳米颗粒后玻璃的结构变化。借助飞秒激光脉冲激发下的Z扫描与光克尔闸技术,在近红外波段下研究了材料的三阶非线性光学特性。研究结果表明银纳米颗粒铋酸盐复合材料有着亚皮秒级的非线性响应时间,并且其非线性折射率γ在纳米颗粒的热电子效应以及局部场效应的影响下,较基质玻璃最高可以提升29倍。     

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.     

Ag-Al纳米球二聚体的光学性质研究

金属纳米材料因其表面等离子体共振特性而备受关注。异质结构的金属纳米材料的光学特性相比于同质结构因其材料的不同破坏了原有结构的对称性,对称性的破坏将引起光学性质的改变,相邻两个颗粒之间的相互作用会产生Fano共振。Fano共振是由异质纳米结构的表面等离子体共振耦合引起的,通过合理地调控表面等离子体共振的耦合,将进一步调控Fano共振的强度同时促使异质结构的电场增强特性和辐射特性得到进一步优化。受金银等贵金属的带间跃迁影响,金属铝纳米材料成为研究紫外-近紫外光区的表面等离子体共振研究最佳选择。采用有限时域差分方法研究了Ag-Al纳米球二聚体的光学特性。研究了Ag和Al纳米球组成的二聚体的吸收光谱与入射光偏振方向、纳米球半径、颗粒间距和介质折射率等几何结构及物理参数的关系,并深入讨论了二聚体的局域场分布规律;讨论了获取更高效的Fano共振光谱的方法。由于材料的对称性被破坏,异质二聚体的光学性质与同质二聚体明显不同,Ag-Al异质纳米球二聚体呈现出在紫外和可见光区的双Fano共振现象。Ag-Al二聚体表面等离子体互相耦合引起Fano共振从而导致表面等离子体的共振抑制和增强。研究结果对在紫外-可见光区的表面等离子体应用、纳米光学器件的设计与开发及基于表面等离子体共振的表面增强光谱、生物传感和检测研究等有一定参考价值。     

光学共振增强的表面铯激活银纳米结构光阴极

金属光阴极因其超短脉冲发射和运行寿命长的特性从而具有重要应用价值,但是较高的功函数和较强的电子散射使其需要采用高能量紫外光子激发且光电发射量子效率极低.本文利用Mie散射共振效应增强银纳米颗粒中的局域光学态密度,提升光吸收率和电子的输运效率,并利用激活层降低银的功函数,从而增强光阴极在可见光区的量子效率.采用时域有限差分方法分析银纳米球阵列的光学共振特性,采用磁控溅射和退火工艺在银/氧化锡铟复合衬底上制备银纳米球,紧接着在其表面沉积制备铯激活层,最后在高真空腔体中测试光电发射量子效率.实验结果表明平均粒径150 nm的银纳米球光阴极在425 nm波长的量子效率超过0.35%,为相同激活条件下银薄膜光阴极的12倍,峰值波长与理论计算的Mie共振波长相符合.     

Deep-ultraviolet surface plasmon resonance of Al and Al_(core)/Al_2O_(3shell) nanosphere dimers for surface-enhanced spectroscopy

The localized surface plasmon resonance properties of Al and Alcore/Al2O3 shell nanosphere dimers with Al and Al core nanosphere radii of 20 nm and Al2O3 shell of 2 nm in the deep-ultraviolet region have been studied using the finite difference time domain method. The extinction spectra and the electric field distribution profiles of the two dimers for various gap distances between two individual nanospheres are compared with those of the corresponding monomers to reveal the extent of plasmon coupling. It is found that with the interparticle distance decreasing, a strong plasmon coupling between two Al or Alcore/Al2O3 shell nanospheres is observed accompanied by a significant red shift in the extinction spectra at the parallel polarization direction of the incident light related to the dimer axis, while for the case of the perpendicular polarization direction, a weak plasmon coupling arises characterized by a slight blue shift in the extinction spectra. The electric field distribution profiles show that benefiting from the dielectric Al2O3 shell, the gap distance of Alcore/Al2O3 shell nanosphere dimers can be tailored to < 1 nm scale and results in a very high electric field enhancement. The estimated surface-enhanced Raman scattering enhancement factors suggests that the Alcore/Al2O3 shell nanosphere dimers with the gap of < 1 nm gave rise to an enhancement as high as 8.1 × 107 for interparticle gap = 0.5 nm. Our studies reveal that the Alcore/Al2O3 shell nanosphere dimers may be promising substrates for surface-enhanced spectroscopy in the deep-ultraviolet region.     

Local field enhancement of pair arrays of silver nanospheres

Local field surface plasmon excitation of pair arrays of silver nanospheres was studied using three-dimensional finite-difference time-domain method. The near-field enhancement was associated with the radius of nanosphere and the incident wavelength, the highest of which always appeared in the penultimate gaps, regardless of the number of the pairs. The surface plasmon resonance could be controlled and tuned by radius of nanosphere and incident wavelength.     

Synthesis of bismuth nanocap arrays on quartz substrates and their surface plasmon resonance properties

Bismuth nanocap arrays have been prepared by vacuum depositing Bi films onto the surfaces of self-assembled monolayer arrays of SiO₂ nanoparticles. The surface morphologies, structures, and optical properties of the obtained samples have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscope (AFM), X-ray diffraction (XRD), and ultraviolet–visible–near infrared (UV–vis–NIR) spectrophotometer. TEM and AFM images indicated that the SiO₂/Bi composite nanoparticles were incompletely encapsulated and their surfaces were relatively rough. UV–vis–NIR absorption spectra showed that Bi nanocap arrays had strong and tunable surface plasmon resonance peaks in the visible and near infrared regions, which were dependent dramatically on the relative ratio of the SiO₂ core diameter to the Bi cap thickness.     

Nanosphere Templated Metallic Grating Assisted Enhanced Fluorescence

In this paper, enhanced fluorescence from a silver film coated nanosphere templated grating is presented. Initially, numerical simulation was performed to determine the plasmon resonance wavelength by varying the thickness of the silver film on top of a monolayer of 400 nm nanospheres. The simulation results are verified experimentally and tested for enhancing fluorescence from fluorescein isothiocyanate whose excitation wavelength closely matches with the plasmon resonance wavelength of the substrate with 100 nm silver film over nanosphere. The 12 times enhancement in the intensity is attributed to the local field enhancement in addition to the excitation of surface plasmon polaritons along the surface.     

多层金属纳米点阵的制备及其光学性质的研究

采用纳米球刻蚀法结合热蒸发技术制备了银和氧化硅交替层叠的纳米颗粒阵列. 扫描隧道显微镜测量结果表明, 该纳米阵列呈锥形多层结构. 分光光度计测量样品表明, 该纳米阵列在近红外波段存在明显的透射谷, 该透射谷来源于金属纳米颗粒局域等离激元的激发, 随着金属/介质层数的增多, 透射谷的位置向短波方向移动. 利用HFSS软件对该纳米阵列进行了仿真, 并分析了透射谷蓝移的原因. 关键词： 纳米球刻蚀技术 金属/介质纳米颗粒 表面等离子激元     

Effect of chromium interlayer deposition on periodic silver nanoparticle array structure fabricated by nanosphere lithography

Effect of chromium interlayer deposition on 2-dimensional, periodic silver nanoparticle array structure was systematically investigated. The silver nanoparticle array was fabricated by nanosphere lithography with assembled polystyrene nanospheres being as a deposition mask. The chromium interlayer was deposited by thermal evaporation either on the nanosphere mask or directly on the silicon substrate. The structures of the achieved silver nanoparticle arrays were characterized by scanning electron microscope and were compared with that of silver nanoparticle array without the interlayer. With analysis of the anomalies among the structures the critical role of the interlayer in the periodic nanoparticle array fabrication was revealed.     

High-absorbing gradient multilayer coatings with silver nanoparticles

We suggest an efficient way to enhance broadband visible light absorption in multilayer nanostructured systems formed by silver nanoparticle arrays. This approach is based on the explicit use of a gradient change in the parameters of the arrays (such as nanoparticle size or concentration). We analytically derive general conditions of the spectral characteristics of individual arrays which must be satisfied for the realization of highly-absorptive gradient multilayer nanostructured coatings. Two specific types of gradient coatings, (i) with the gradient of the size of the silver nanoparticles in the arrays and (ii) with the gradient of their surface concentration, are numerically studied in detail. The obvious advantages of the size-gradient coatings are revealed, in particular their total thickness of less than a wavelength. Multilayer coatings with a concurrent gradient of both concentration and mean particle size are fabricated from silver island films and their high and broadband absorption is demonstrated experimentally. PACS 78.67.Pt; 78.67.-n; 73.20.Mf; 42.25.Bs     

Extraordinary optical transmission in the ultraviolet region through aluminum hole arrays

We investigated the extraordinary optical transmission phenomenon in the UV range by fabricating large-area, free-standing aluminum hole arrays using extreme UV interference lithography and shadow thermal evaporation. Transmission spectra show strong peaks in the UV region resulting from both surface plasmon polariton and localized surface plasmon excitations. The results indicate that the high plasmon frequency of Al is directly responsible for the presence of strong resonance peaks in the UV region, which supports the role of plasmonic phenomena in the extraordinary transmission. The simple fabrication method enables large-area production of such structures for research and industrial production purposes.