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.     

Fano-like resonance characteristics of asymmetric Fe_2O_3@Au core/shell nanorice dimer

A geometrical configuration of Fe2O3/Au core-shell nanorice dimer is proposed and its multipolar plasmon Fano- like resonance characteristics are theoretically investigated by generalizing the plasmon hybridization model of individual nanorice to the bright and dark modes of the nanorice dimer. Under the irradiation of polarization light, the extinction spectra of the nanorice dimer are numerically simulated by using the finite element method （FEM）. Our studies show that the Fano-like resonance of the nanorice dimer results in an asymmetric line shape of the Fano dip in the extinction spectrum which can be controlled by varying the structure parameters of the nanorice dimer. Meanwhile, there is a giant field enhancement at the gap between the two nanorices on account of the plasmonic coupling in the nanorice dimer. The aforementioned two characteristics of the nanorice dimer are useful for plasmon-induced transparency and localized surface plasmon resonance sensors.     

银纳米粒子阵列中衍射诱导高品质因子的四偶极晶格等离子体模式

金属纳米颗粒阵列中形成的四偶极晶格共振模式具有低辐射损耗、高品质因子的特性,因此广泛应用于纳米激光、传感、固态照明等领域.基于时域有限差分法在均匀环境下研究了银纳米圆柱阵列的光谱与近场特性.研究结果表明,在x偏振光直入射下,通过调节阵列x方向的周期,共振强度先增加后降低,当两个方向上的周期相等时,提出的阵列结构能够产生一个线宽约0.4 nm、品质因子高达1815的四偶极晶格共振模式,这种共振模式呈现出Fano线型的透射谷;调控y方向的周期能够实现从Fano线型的透射峰到透射谷的转变.本文说明了粒子大小、晶格周期对四偶极晶格共振模式的重要性,同时为银纳米颗粒在可见光波段设计高品质因子共振提供了优化策略.     

Surface plasmon resonance of Ag nanoparticles in the vicinity of a high impedance surface

Surface Plasmon resonance of Ag nanoparticles in the vicinity of a high impedance surface is investigated. Mushroom-like nanostructures were vertically grown on silicon substrate to form a high impedance surface operating in the range of optical frequencies. Formation of Ag nanoparticles on the fabricated high impedance surface was realized using plasma bombardment process. Optical measurements show an enhancement in the surface plasmon resonances of Ag nanoparticles. Also it was shown that the plasmon resonance peak of the Ag nanoparticles shifts to blue when Ag nanoparticles approach to the high impedance surface.     

Tunable surface-plasmon-resonance wavelength of silver island films

This paper experimentally and theoretically investigates the effect of the underlayer medium on tuning of the surface plasmon resonance (SPR) wavelength of silver island films,and the effect of substrate temperature on the morphologies and optical properties of the films.From the absorption spectra of single Ag with various thickness and overcoated (Ag/TiO 2) films deposited on glass substrates at various substrate temperatures by RF magnetron sputtering,we demonstrate that the surface plasmon resonance wavelength can be made tunable by changing the underlayer medium,the thickness of metal layer and the substrate temperature.By varying substrate temperatures,the interparticle coupling effects on plasmon resonances of nanosilver particles enhance as the spacing between the particles reduces.When the substrate temperature is up to 500 C,the absorption peak decreases sharply and shifts to shorter wavelength side due to the severe coalescence between silver islands in the film.     

One‐electron Optical Properties of a Nanorice with a Nonconcentric Core

We investigate optical properties of nanoshells (small composite clusters composed of a dielectric core and a metal shell; contribution of the shell dominates in the optical properties of the whole cluster) far from plasmon resonance. In particular, nanoshells with the shape of a stretched rotation ellipsoid (nanorice) are considered. For such shell‐type particle the electron wavefunction, the electron energy, the wavenumber spectrum, and the matrix elements of corresponding optical transitions were found. Using these quantities, the classical optical conductivity of such shells (the quantum effects are not considered) and the quantum optical conductivity (relevant addendums for the classical conductivity that are caused by the quantum effects like the electron spectrum discreteness) were found. Oscillating nature of the dependence of these addendums on the incident light frequency is established. The optical conductivity expressions are generalized for the case of a nanorice particle with a weak nonconcentricity.     

Design of Highly Sensitive Surface Plasmon Resonance Sensors Using Planar Metallic Films Closely Coupled to Nanogratings

We investigate the sensitivity enhancement of surface plasmon resonance （SPR） sensors using planar metallic films closely coupled to nanogratings. The strong coupling between localized surface plasmon resonances （LSPRs） presenting in metallic nanostructures and surface plasmon polaritons （SPPs） propagating at the metallic film surface leads to changes of resonance reflection properties, resulting in enhanced sensitivity of SPR sensors. The effects of thickness of the metallic films, grating period and metal materials on the refractive index sensitivity of the device are investigated. The refractive index sensitivity of nanograting-based SPR sensors is predicted to be about 543 nm/RIU （refractive index unit） using optimized structure parameters. Our study on SPR sensors using planar metallic films closely coupled to nanogratings demonstrates the potential for significant improvement in refractive index sensitivity.     

Optical Properties of Plasmon Resonances with Ag/SiO2/Ag Multi-Layer Composite Nanoparticles

Optical properties of plasmon resonance with Ag/SiO2/Ag multi-layer nanoparticles are studied by numerical simulation based on Green＇s function theory. The results show that compared with single-layer Ag nanoparticles, the multi-layer nanoparticles exhibit several distinctive optical properties, e.g. with increasing the numbers of the multi-layer nanoparticles, the scattering efficiency red shiRs, and the intensity of scattering enhances accordingly. It is interesting to find out that slicing an Ag-layer into multi-layers leads to stronger scattering intensity and more ＂hot spots＂ or regions of stronger field enhancement. This property of plasmon resonance of surface Raman scattering has greatly broadened the application scope of Raman spectroscopy. The study of metal surface plasmon resonance characteristics is critical to the further understanding of surface enhanced Raman scattering as well as its applications.     

脉冲激光沉积Ag:BaTiO3纳米复合薄膜及其光学特性

在MgO(100)基片上利用脉冲激光沉积技术制备了掺有Ag纳米颗粒的BaTiO₃复合薄膜.通过X射线衍射对薄膜的结构进行了表征,利用透射电子显微镜对Ag纳米颗粒的尺寸、形态进行了观测,X射线光电子能谱结果表明Ag呈金属态.在410—500nm范围内观测到了Ag纳米颗粒引起的等离子振荡峰,随着后处理温度和Ag颗粒浓度的增加,吸收峰发生红移,并出现了双峰现象. 关键词： 金属纳米复合薄膜 激光沉积 光吸收     

Strong Exciton-Plasmon Coupling and Hybridization of Organic-Inorganic Exciton-Polaritons in Plasmonic Nanocavity

We investigate strong exciton-plasmon coupling and plasmon-mediated hybridization between the Frenkel(F)and Wannier-Mott(WM)excitons of an organic-inorganic hybrid system consisting of a silver ring separated from a monolayer WS_2 by J-aggregates.The extinction spectra of the hybrid system calculated by employing the coupled oscillator model are consistent with the results simulated by the finite-difference time-domain method.The calculation results show that strong couplings among F excitons,WM excitons,and localized surface plasmon resonances(LSPRs) lead to the appearance of three plexciton branches in the extinction spectra.The weighting efficiencies of the F exciton,WM exciton and LSPR modes in three plexciton branches are used to analyze the exciton-polaritons in the system.Furthermore,the strong coupling between two different excitons and LSPRs is manipulated by tuning F or WM exciton resonances.     

银/二氧化钛核壳纳米颗粒对碲化镉纳米晶的荧光增强研究

利用新合成的复合纳米结构银/二氧化钛核壳纳米颗粒,研究了金属银纳米颗粒对碲化镉纳米晶层荧光的增强情况.结果表明,这种新型复合金属纳米结构能极大地增强发光纳米晶层的荧光强度.银/二氧化钛核壳纳米颗粒是以水合肼、硝酸银和四异丙氧基钛为原材料,利用胶体化学法在水溶液中合成.透射电子显微镜图片表明这种新合成的银/二氧化钛纳米材料基本上呈球形,有较为明显的核壳结构,中间黑色的核是银纳米颗粒,外层颜色较浅部分是二氧化钛壳层.另外,包裹二氧化钛壳层后,银纳米颗粒的表面等离子吸收带从409 nm红移至430 nm,也证实了这种新型核壳纳米材料的形成.将此合成方法得到的银/二氧化钛纳米颗粒和碲化镉纳米晶用旋转涂覆方法进行直接组合后,得到了银纳米颗粒对碲化镉纳米晶荧光的明显增强,并对其增强的物理过程进行了讨论.这种能够增强荧光团发光的新型复合银纳米结构将在发光器件、荧光成像、生物探测等方面具有一定的应用价值.     

Plasmonic tuning of aluminum doped zinc oxide nanostructures by atomic layer deposition

Currently there is a strong interest in plasmonic materials operating in the near‐infrared (NIR), however, conventional metals such as gold and silver possess high optical losses in this region. In this work we demonstrate localized surface plasmon resonances (LSPRs) with low loss in the NIR region by utilizing atomic layer deposition to deposit thin films of aluminium doped zinc oxide onto silicon nanopillars created via nanopshere lithography. The deposited films have excellent conformality and the LSPRs can be tuned from the mid‐infrared to the NIR by controlling the doping concentration, deposition temperature and nanostructure morphology. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Ag:Bi2O3复合膜的线性和非线性光学性质

从实验和理论两个方面，探讨了金属Ag不同掺杂浓度对Ag:Bi₂O₃复合膜线性和非线性光学性质的影响. 用吸收光谱研究了Ag浓度与Ag:Bi₂O₃复合膜表面等离子体共振带之间的关系；用皮秒Z-扫描技术研究了共振和非共振情况下(激发光波长分别为532nm和1064nm)，金属Ag浓度与复合膜三阶非线性极化率的关系. 基于表面等离子体共振理论和局域场增强理论对复合膜进行了分析，得到了不同Ag浓度时Ag:Bi₂O₃复合膜的三阶非线性效应，研究了激发波长和金属浓度对复合膜线性和非线性光学性质的影响. 结果表明，等离子体共振增强和合适的金属掺杂浓度使得三阶极化率增强二个量级，在Ag浓度为35％左右和接近等离子体共振频率(相应吸收带位于560nm—622nm)的532nm激发时，χ⁽³⁾具有最大值2.4×10^-9esu. 关键词： 金属纳米颗粒 复合膜 三阶非线性 表面等离子体共振     

The color of finely dispersed nanoparticles

We discuss the dependence of the color of low-concentrated nanoparticle systems on particle size and mass concentration for Ag, Au and TiN nanoparticles, which exhibit a surface plasmon polariton resonance in extinction spectra. Comparison is made with color data obtained for Ag and Au colloidal suspensions. When particles lump into aggregates, the splitting of the surface plasmon resonance into new resonances affects the extinction of light and, hence, the color of the particle assembly. This is demonstrated for aggregated colloidal suspensions of Ag and Au nanoparticles. Finally, for highly concentrated assemblies such as pigment films, we discuss the dependence of the color in diffuse reflectance and transmittance according to Kubelka and Munk (P. Kubelka, F. Munk: Z. Techn. Phys. 12, 593 (1931)), and extend this model by using optical properties of aggregates of spheres. Received: 2 July 2001 / Published online: 10 October 2001     

Surface‐enhanced Raman scattering studies of carbon nanotubes using Ag‐core Au‐shell nanoparticles

Surface‐enhanced Raman scattering from carbon nanotube bundles adsorbed with plasmon‐tunable Ag‐core Au‐shell nanoparticles (Ag@Au nps) was carried out for the first time. By utilizing nanoparticles whose plasmon resonance peak (541, 642 nm) closely matches the commonly used Raman excitation sources (532, 632.81 nm), we can observe a large enhancement in the Raman signatures of carbon nanotubes. We obtain greater enhancement in the Raman signal for the above case when compared to nanotubes adsorbed with conventional Ag, Au or other ‘off resonant’ Ag@Au nps. The power‐dependent SERS experiment on single‐walled nanotubes (SWNTs) with resonant Ag@Au nps reveals a linear behavior between the G‐band intensity and the photon flux density, which is in agreement with the vibrational pumping model of SERS. The observed enhancement by resonance matching is pronounced for carbon nanotubes and may lead to insights into understanding nanotube–nanoparticle interaction. Copyright © 2009 John Wiley & Sons, Ltd.     

Ag纳米颗粒增强的Ho~(3+)/Tm~(3+)共掺铋锗酸盐玻璃的2μm发光研究

采用基于传统熔融淬冷技术的热化学还原法制备了系列Ag纳米颗粒复合Ho3+/Tm3+共掺铋锗酸盐玻璃样品,研究了Ag纳米颗粒含量对玻璃2μm发光特性的影响.结果表明,Ag纳米颗粒的表面等离子体共振带位于500—900 nm,峰值位于650 nm,透射电子显微镜图像中观察到均匀分布的Ag纳米颗粒,尺寸约为5—10 nm.通过测试玻璃样品在1.7—2.3μm波段的荧光光谱发现,Ag掺杂后Ho3+离子2μm处的荧光强度得到了极大的提高,其中AgCl掺杂质量分数为0.3%时的荧光强度比未掺杂时的荧光强度增强10倍,这归因于Ag纳米颗粒的局域场增强作用.计算得到Ho3+离子的吸收截面为0.491×10-20cm-2,发射截面为1.03×10-20cm-2,当增益系数为0.2时即可实现正的增益.     

Preparation of monodisperse bimetallic nanorods with gold nanorod core and silver shell and their plasmonic property and SERS efficiency

In this study, monodisperse bimetallic nanorods with gold (Au) nanorod core and silver (Ag) shell (Au@AgNRs) were synthesized through seed‐mediated growth process by reduction of AgNO₃ using Au nanorods with narrow size and shape distribution as seeds. With increasing the used amount of AgNO₃, the Ag shell thickness of their lateral facets is raised faster than that of their two tips, leading to a decrease of their aspect ratios. Four plasmon bands are observable on the extinction spectra of Au@AgNRs, which are attributed to the longitudinal dipolar plasmon mode, transverse dipolar plasmon mode, and octupolar plasmon mode of the core‐shell structured bimetallic nanorods, respectively. As their Ag shell thickness increases, their longitudinal plasmon band blue‐shifts notably with the transverse plasmon band blue‐shifting and the two octupolar plasmon bands red‐shifting slightly, due to the decrease of their aspect ratios and enhancement of Ag plasmon resonance contribution. When used as surface‐enhanced Raman scattering (SERS) substrate for probing minute amounts of 4‐mercaptobenzoic acid in aqueous solution, Au@AgNRs have much stronger SERS activity than Au nanorods, and the obtained Raman signals are highly reproducible arising from their excellent monodispersity. Their SERS activity is remarkably increased with their Ag shell thickness thanks to the enhancing surface electric field and the chemical enhancement associated with electronic ligand effect. Copyright © 2014 John Wiley & Sons, Ltd.     

Optical properties of the Au–Ag alloy nanowire coated with an anisotropic shell

The optical properties of the Au–Ag alloy nanowire coated with a cylindrical shell with radial dielectric anisotropy are investigated based on quasistatic theory. Numerical results show that the surface plasmon resonance (SPR) peak is redshifted with increasing the component ratio of Au in the alloy, while the intensity of extinction section at the SPR increases with increasing the component ratio of Ag in the alloy. In addition, as the extent of anisotropy of the shell increases, the extinction section at SPR wavelength decreases and the SPR wavelength is redshifted, but compared with the isotropic shell consisting of comparable dielectric constant materials, the SPR has a distinct blueshift for anisotropic shell. We also find that the field enhancement can be completely concentrated inside the anisotropic shell and the electromagnetic transparency can be exhibited.     

On the extinction multipole plasmons in gold nanorods

On the basis of the T-matrix formalism and numerical simulations, we derive an explicit rule for partial multipole contributions to the plasmon resonances of gold nanorods at a fixed or random orientation. The parity of a given spectral resonance number n coincides with the parity of their multipole contributions l, where l is equal to or greater than n, and the total resonance magnitude is determined by the lowest multipole contribution. We also investigate the dependence of multipole plasmons on the size, shape, and orientation of nanorods with respect to the polarized incident light. It is shown that the multipole resonance wavelengths as a function of the aspect ratio divided by the resonance number collapse onto one linear scaling curve. This scaling is explained by using the plasmon standing wave concept introduced by Schider et al. [Plasmon dispersion relation of Au and Ag nanowires. Phys Rev B 2003;68:155427].     

Engineering the plasmon resonance of large area bimetallic nanoparticle films by laser nanostructuring for chemical sensors

Large area fabrication of metal alloy nanoparticles with tunable surface plasmon resonances on low-cost substrates is reported. A UV excimer laser was used to anneal 5 nm thick Ag Au bilayer films deposited with different composition ratios to create alloy nanoparticles. These engineered surfaces are used to investigate how the wavelength of the surface plasmon resonance affects the optical detection capability of chemical species by surface-enhanced Raman spectroscopy.