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.     

Highly enhanced surface plasmon resonance in a coupled silver nanodumbbell

Scattering field interactions and surface plasmon resonance in a coupled silver nanodumbbell (a pair of silver nanosphere connected by a silver nanobar) are simulated by using the three-dimensional finite-element method. The enhancement of scattering cross section which exhibits a blue-shifted is associated with the diameter of the silver nanobar and the wavelength of incident light. Interestingly, the generated optical cloud exceeds two times of the nanodumbbell size which can be turned by varying the diameter of the silver nanobar.     

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     

A computational study of the optical response of strongly coupled metal nanoparticle chains

We study the optical response of strongly coupled metal nanoparticle chains using rigorous multiple scattering calculations. The collective resonant frequency of silver nanosphere chains and the coupling between chains are considered. The coupling between silver nanoparticle chains are understood by the transmission and reflection calculations of 2D periodic arrays of nanospheres. The results are in agreement with recent experiments. The splitting of plasmon resonance modes for different polarizations of the incident light are explored. Our results show that the transverse mode resonant wavelength is very sensitive to the inter-chain distance. Results on the effect of disorder are also presented.     

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.     

Optical Tunability of Silver-Dielectric-Silver Multi-Layered Cylindrical Nanotubes Using Quasi-Static Approximation

Local surface plasmon resonances(LSPRs) of silver-dielectric-silver multi-layered(SDS-ML) nanotubes are studied by theoretical calculations. Based on quasi-static approximation, the absorption cross section of SDS-ML nanotubes is plotted as a function of wavelength. The results show that SDS-ML nanotubes exhibit strong coupling between the cylindrical silver and nanotubes. The absorption spectra of LSPRs are strongly influenced by changing the radius of the inner core and outer nanotube shell. The longer wavelength is red-shifted by increasing the radius of the inner core and outer shell, while the short wavelength shows the opposite properties.These phenomena are explained by the plasmon hybridization theory. In addition, for clarity, the distributions of electric field intensity at their plasmon resonance wavelengths are also studied.     

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。     

Efficient surface plasmon amplification from gain-assisted gold nanorods

We report on the efficient surface plasmon amplification by stimulated emission of radiation (spaser) from a gold nanorod coated with proper gain media. Numerical simulations show that the threshold of the nanorod-based spaser is nearly 1 order of magnitude lower than that of the core-shell nanosphere, which is verified by analysis with electrostatic theory. Furthermore, it is found that the nanorod-based nanosystem possesses unique optical properties such as wavelength tunability and polarization sensitivity.     

金属表面等离体子振荡

深入浅出地分析了金属表面等离体子振荡形成的机理，利用拉普拉斯方程得到了半无限金属、金属薄膜和球状纳米金属颗粒的表面等离体子振荡频率。     

表面等离子激元非线性表面增强拉曼散射效应

本文采用热蒸发法制备得到纳米Ag颗粒作为增强拉曼衬底, 利用入射光子与纳米颗粒表面价电子的相互作用机理, 激发出高能表面等离子激元, 其表面等离子形成的高能"热点"起到表面增强拉曼散射效果. 通过比较不同入射光强下的拉曼峰强, 指出纳米Ag颗粒的增强拉曼散射效果可以实现低探测光强下的高散射强度, 即纳米Ag颗粒的表面等离子激元具有非线性的表面增强拉曼散射效果, 可降低对样品的光、热损伤, 以利于拓展拉曼散射光谱的应用范围. 同时比较不同纳米Ag颗粒衬底的表面增强拉曼散射效果表明, 采用的热蒸发工艺具有较大的工艺域度, 具有较强的工艺兼容性.     

Polarization Bremsstrahlung radiation on a nanosphere in a dielectric

Within the limits of a new approach based on the Mie scattering theory, polarization bremsstrahlung radiation (PBR), arising during electron scattering on a metallic nanosphere with radius from 10 to 100 nm placed in a dielectric medium is theoretically investigated. The spectral range close to the plasmon resonance is considered, where the contribution of the polarized channel to bremsstrahlung radiation dominates. Spectral, velocity, and angular PBR characteristics are calculated. The sensitivity of the PBR spectrum to the dielectric permittivity of the medium surrounding the nanosphere is demonstrated.     

Surface plasmon interference pattern on the surface of a silver-clad planar waveguide as a sub-micron lithography tool

A new sub-micron photolithography tool has been realized by utilizing the interference of surface plasmon waves(SPWs) on the near surface of a silver(Ag)-clad ultraviolet(UV) planar waveguide.A laser beam with a wavelength of 325 nm was incident into the waveguide core,and suffered a series of total internal reflections on the interfaces between the waveguide core and the cladding layers.The incident light and the reflected light induced two beams of SPWs traveling in contrary directions,which interfered wi...     

Calculation of curvature dependent surface plasmon resonance in gold nanospheroid and nanoshell

In this paper, theoretical calculations based on dipole-limit are performed to investigate the effects of curvature on the surface plasmon resonance (SPR) properties of nanometer size gold spheroid and shell. By comparing the aspect ratio with the shell thickness, we demonstrated that the curvature radius is a common better factor that can be used to predict the SPR wavelength and shift fashion. For nanospheroid, increasing the ratio of curvature radius corresponding to the climaxes leads to an increase in the ratio of SPR wavelength, whereas increasing the ratio of curvature radius of outer and inner surface in nanoshell leads to an decrease in the ratio of SPR wavelength. As a morphologic factor, curvature radius plays an important role in affecting the distribution of electron density, and consequently controlling the SPR frequency.     

Near-field plasmonic coupling for enhanced nonlinear absorption by femtosecond pulses in bowtie nanoantenna arrays

Plasmonic bowtie nanoantennas (BNAs) can exhibit a strong enhancement of optical field, leading to large nonlinear effects. We investigated the nonlinear optical absorption of an array of BNA by femtosecond pulses, using the open-aperture Z-scan technique. The BNA array composed of paired gold nanotriangles was fabricated by nanosphere lithography. We experimentally demonstrated that upon decreasing the gap width, nonlinear absorption is enhanced due to both the enhancement of near-field coupling of nanoantennas and the minimum of the spectral detuning between the center wavelength of the laser for excitation and the localized surface plasmon resonances. The role of near-field resonant plasmonic coupling in BNA is analyzed theoretically and confirmed by our simulations.     

High sensitivity refractive index gas sensing enhanced by surface plasmon resonance with nano-cavity antenna array

The surface plasmon resonance gas sensor is presented for refractive index detection using nano-cavity antenna array.The gas sensor monitors the changes of the refractive index by measuring the spectral shift of the resonance dip,for modulating the wavelength of incident light.It is demonstrated that minute changes in the refractive index of a medium close to the surface of a metal film,owing to a shift in the resonance dip of the wavelength,can be detected.The average detection sensitivity is about 3200 nm/RIU(refractive index units),which is more than twice that of a metal grating-based gas sensor.The reflectivity of the surface plasmon resonance dip is only ～ 0.03%,and the full widths at half maximum(FWHMs) of bandwidth of the angle and wavelength are ～ 0.20° and 4.71nm,respectively.     

偏振控制光强调制型点阵SPR传感器研究

介绍了一种偏振控制光强调制型点阵表面等离子体共振(SPR)传感器,分析了入射角度、金膜厚度、起偏器设置、光源波长及数据处理方式对传感器灵敏度和线性范围的影响,并对632.8 nm与740 nm两种光源传感器系统进行了实验测试与分析.结果表明,偏振控制光强调制型点阵SPR传感器可将光经过表面等离子体共振所产生的偏振态变化...     

Surface plasmon characteristics of tunable photoluminescence in single gold nanorods

Light emission resulting from two-photon excited gold nanoparticles has been proposed to originate from the radiative decay of surface plasmon resonances. In this vein, we investigated luminescence from individual gold nanorods and found that their emission characteristics closely resemble surface plasmon behavior. In particular, we observed spectral similarities between the scattering spectra of individual nanorods and their photoluminescence emission. We also measured a blueshift of the photoluminescence peak wavelength with decreasing aspect ratio of the nanorods as well as an optically tunable shape-dependent spectrum of the photoluminescence. The emission yield of single nanorods strongly depends on the orientation of the incident polarization consistent with the properties of surface plasmons.     

Resonant surface plasmons of a metal nanosphere treated as propagating surface plasmons

On the assumption that the resonant surface plasmons on a spherical nanoparticle are formed by standing waves of two counter-propagating surface plasmon waves along the surface, by using Mie theory simulation, we find that the dispersions of surface plasmon resonant modes supported by silver nanospheres match with those of the surface plasmons on a semiinfinite medium-silver interface very well. This suggests that the resonant surface plasmons of a metal nanosphere can be treated as a propagating surface plasmon wave.     

Nanosphere dispersion on a large glass substrate by low dose ion implantation for localized surface plasmon resonance

Dispersing nanospheres on a large glass substrate is the key to fabricate noble metal nanostructures for localized surface plasmon resonance through dispersed nanosphere lithography. This article reports that by modifying the glass surface with low dose ion implantation and successively dip coating the surface with poly(diallyldimethyl ammonium chloride) (PDDA), polystyrene or silica nanospheres can be dispersed on a large glass substrate. Investigation shows that several kinds of ions, such as silicon, boron, argon, and arsenic, can improve the nanosphere dispersion on glass, attributed to the ion bombardment-caused silicon increment. Ion implantation imposes no surface roughness or optical loss to the glass substrate, thus this method is suitable for localized surface plasmon resonance application. Experiments show silicon ion implantation can best disperse the nanospheres. For the gold nanostructures obtained by obliquely evaporating 30 nm of gold film onto the polystyrene nanospheres, which are dispersed on a silicon ion implanted glass substrate, a localized surface plasmon resonance sensitivity of 242 nm/RIU is achieved.     

Three-dimensional analysis of silver nano-particles doping effects on super resolution near-field structure

The super resolution near-field structure which incorporates a AgOx thin film was studied through the calculation using three-dimensional (3D) finite-difference time-domain method. The influences of the optical field distribution generate by some factors, e.g., the polarization direction, the wavelength of incident light and the size of silver nano-particles, which are sensitive to the surface plasmon resonance are discussed in detail. The goal of this study is to explain the physical mechanisms responsible for the super-resolution near-field structure phenomena in 3D model and give a better understanding of the optical properties between AgOx layer and incident light.