金和银纳米粒子二维周期阵列的光学性质

本文利用离散点偶极子近似方法(DDA)研究了金和银纳米粒子二维周期阵列的光学性质。研究结果表明二维周期阵列的消光性质及其表面等离子共振(SPR)波长受到阵列内粒子组成材料、粒子形状尺寸、阵列周期和阵列排布方式等因素的影响。对于二维正方阵列,当周期较小时(一般小于300 nm),阵列的共振波长主要取决于粒子组成材料和形状尺寸;当周期与阵列单体的共振波长附近时,阵列的消光谱中会出现极窄且锐的SPR共振峰,峰位只与阵列的周期值相关。改变阵列在平行和垂直于入射光偏振方向的周期,可以方便地调节二维长方阵列的共振峰的峰位和峰宽。     

Modeling of light absorption and scattering by metal nanoparticles coated with organic dye J-aggregate

The results of the theoretical study of optical properties of composite nanoparticles consisting of a metal core (Ag, Au, Cu, Al, Ni, Cr) and a J-aggregate shell of organic dye are presented. Light extinction, absorption, and scattering coefficients in colloidal solutions were calculated within the model based on the Mie theory modified taking into account dimensional phenomena and complemented by calculations of complex dielectric functions of the metal core and J-aggregate shell. The model adequately explains the features observed in light absorption and scattering spectra by hybrid nanoparticles, associated with the plasmon resonance in the metal core and with electronic excitation of the J-aggregate. The strong dependence of the results on geometrical parameters of nanoparticles and dielectric constants of core and shell materials was demonstrated. Methods for controlling the effects of the plasmon-exciton interaction in the system and optical properties of composite materials developed based on nanoparticles under study are discussed.     

Enhancement of Nonlinear Optical Effects in Porous Composite Plasmonic Structures

A method for formation of bulk plasmonic structures based on porous quartz with silver nanoparticles in pores has been proposed and implemented. The spectroscopy of their optical and nonlinear optical properties has been performed by methods of second harmonic generation and two-photon absorption. A significant increase in the nonlinear absorption coefficient has been detected in the plasmon resonance region. The enhancement of the second optical harmonic has been observed with the shift by tens of nanometers from the plasmon resonance position toward the long-wavelength region.     

Composite‐Assisted Phase‐Matching: Efficient Wavelength Conversion in Nonlinear Optical Composite Materials Containing Metal Nanoparticles

A novel phase‐matching scheme which is based on the dispersion compensation in the nonlinear optical composite materials containing metal nanoparticles is proposed. Anomalous dispersion originating from the plasmon resonance in metal nanoparticles compensates the dispersion of the host nonlinear material, leading to the perfect phase‐matching and high efficiency of nonlinear optical wavelength conversion. The effectiveness of this approach is theoretically demonstrated, taking third‐order nonlinear processes such as the direct third‐harmonic generation and four‐wave mixing in ZnO composites containing silica‐core–silver‐shell nanoparticles as examples. The results show that with the proposed phase‐matching scheme, unprecedentedly high conversion efficiency can be obtained compared with preceding results in third‐order nonlinear optical solid‐state materials.     

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.     

Nonlinear optical response from composites based on nanostructures consisting of an absorbing core and metallic shell near the plasmon resonance

The object of experimental study and numerical simulation is the nonlinear optical response from composites with nanoparticles consisting of a nonlinearly absorbing dielectric core and a metallic shell. It is shown that a small spread in nanoparticle sizes near the plasmon resonance may significantly change the dependence of the nonlinear optical response on the concentration of nanoparticles of each size.     

Tuning the optical properties of Fe-Au core-shell nanoparticles with spherical and spheroidal nanostructures

Present research interest is to highlight on the manufacturing of core-shell nanoparticles because of core activity with unique properties and surface modification by a shell in the diverse fields (e.g. optoelectronic, catalysis and magneto-optics). In addition, the combined optical properties of magnetic-plasmonic core-shell NPs make them ideal candidates for many applications in biomedical fields. The influence of Fe-core and Au-shell for the formation of the core-shell viz. spherical and spheroidal nanostructures is studied using the discrete dipole approximation method. DDA is an approximation method and its accuracy is compared to Mie theory results for spherical core-shell NPs as Mie theory gives the exact solution to spherical targeted NPs. DDA calculations are further extended to spheroidal core-shell nanostructures. It is observed that the localized surface plasmon resonance (LSPR) peak position in considered core-shell nanostructures is enhanced by changing the cores and shell thickness in the core-shell spherical nanostructures and aspect ratio as well as shell thickness in spheroidal core-shell nanostructures. The absorption spectra are found between 363–788 nm wavelength ranges and can be tuned into UV-visible-near-infrared region of the electromagnetic (EM) spectrum in accordance with desired applications. It has been found that the Fe@hollow@Au and prolate core-shell nanostructures show enhancement to LSPR peaks, bandwidth and their corresponding intensities in comparison to other considered spherical and spheroidal core-shell nanostructures. Tunability in core size, shell thickness, aspect ratio, and configuration will open new potential uses of suitable magnetic-plasmonic core-shell nanostructures in cancer therapy, tissue engineering, drug delivery, and many more of biomedical fields.     

Design and synthesis of plasmonic magnetic nanoparticles

Core–shell nanoparticles containing both iron oxide and gold are proposed for bioseparation applications. The surface plasmon resonance of gold makes it possible to track the positions of individual particles, even when they are smaller than the optical diffraction limit. The synthesis of water-dispersible iron oxide-gold nanoparticles is described. Absorption spectra show the plasmon peaks for Au shells on silica particles, suggesting that thin shells may be sufficient to impart a strong surface plasmon resonance to iron oxide-gold nanoparticles. Dark field optical microscopy illustrates the feasibility of single-particle detection. Calculations of magnetophoretic and drag forces for particles of different sizes reveal design requirements for effective separation of these small particles.     

Surface effect on the size evolution of surface plasmon resonances of Ag and Au nanoparticles dispersed within mesoporous silica

The optical absorption has been investigated for silver and gold nanoparticles dispersed within the pores of monolithic mesoporous silica after annealing at different temperatures. It has been shown that with reduction of the particle size, the surface plasmon resonance position blue-shifts first and then red-shifts for silver/silica samples, but only red-shifts for gold/silica samples. This size evolution of the resonance is completely different from that previously reported for fully embedded particles. Based on the interaction of the particle surface with ambient air and the porosity at the particle/matrix interface, we present a multi-layer core/shell model and assume that the chemical adsorption of gas molecules from the air on the free surface of nanoparticles within the pores is mainly responsible for the observed size evolution of the resonance.     

Surface plasmon tunneling through a touching gold nanocylinder array on a thin gold film

The optical property of a structure composed of a touching gold nanocylinder array on a thin gold film is investigated using finite-difference time-domain (FDTD) method. It is discovered that the transmission behavior can be tuned by tuning the geometry of the structure. As the film thickness increases, the transmission mode associated with the localized surface plasmon resonance blue shifts accompanied with a decrease of magnitude and full width at half maximum, and a second transmission appear due to the interaction of the plasmons on the cylinder with their images induced on the film. The localized waveguide resonance diminishes but the second resonance peak is intensified and broadened noticeably with the separation of the cylinder array and film increase. The cylinder radius size influences the localized surface plasmon resonance mode obviously. These results may be helpful for the design of a novel optical device.     

Influence of phase transitions on the second harmonic generation in metal nanoparticles

In this work we use nonlinear optical properties of Ga nanoparticles monolayers of different average sizes embedded in dielectric matrices to investigate the liquid-solid phase transitions in these materials. Ga nanoparticles, formed by exploiting the partial wetting of liquid Ga over a SiO_x surface are irradiated with fs laser pulses from a Ti:sapphire source. The resulting Second Harmonic (SH) generated in the reflection and transmission directions is measured along the phase transitions by cooling the sample from 320 K down to liquid nitrogen temperature. Hysteresis cycles are observed in the nonlinear transmission, which exhibit a strong amplification from the solid to liquid values as compared to the linear optical results. A simple model for SH generation, based on Mie scattering calculations which includes the effect of surface plasmon resonance provides a fair key for the interpretation of the observed effects.     

后退火处理对铟锡氧化物表面等离激元共振特性的影响

近年来,表面等离激元光子学发展迅速,并取得了众多新成果.重掺杂半导体材料的表面等离激元共振性质的研究,也得到了人们越来越多的关注.本文通过纳米球刻印技术制备准三维二氧化硅纳米球阵列,在阵列上沉积铟锡氧化物薄膜,通过不同条件下的后退火处理改变铟锡氧化物薄膜的载流子浓度和载流子迁移率,并研究随着材料性质的改变其相应表面等离激元共振特性的变化规律.结果表明：退火处理均使铟锡氧化物薄膜的晶粒长大,光学透过率增加;在空气中退火会导致铟锡氧化物薄膜的载流子浓度减少,其表面等离激元共振峰红移;而真空退火则使铟锡氧化物薄膜的载流子浓度增加,共振峰蓝移.这些研究结果可为后续铟锡氧化物表面等离激元材料及器件的研究提供科学依据和实际指导.     

Electronic excitations and optical response of metal nanocomposites under heavy ion implantation

The optical transmission and ion-induced luminescence under implantation of copper ions into quartz glass (a-SiO₂) have been measured to study the processes of formation of copper nanoparticles. It is shown that in situ measurements are more informative in comparison with the ordinary approach—investigation of the properties of ion-implanted nanocomposites only after implantation. A series of experiments was performed to prove that the ion-induced luminescence band at 545–550 nm is due to Cu⁺ ions dissolved in a-SiO₂. The combined use of in situ optical techniques makes it possible to monitor the states of implanted copper (metal nanoparticles and dissolved atoms) by the change in the optical absorption near the surface plasmon resonance of nanoparticles and by the intensity of ion-induced luminescence of Cu⁺ states in solid solution. It is shown that the optical bands of defects, dissolved copper, and nanoparticles can be separated within a simple linear approximation. Near the surface plasmon resonance and defect bands, ion-induced transient optical absorption has been revealed. The transient optical absorption near the surface plasmon resonance is explained by the temperature effect. The relationship between the electronic excitation, radiation-induced optical response, and the kinetics of nanoparticle formation is analyzed. Several stages of nanoparticle formation have been established: accumulation of implanted copper in solid solution, nucleation of nanoparticles, coalescence, growth of nanoparticles, and saturation of nanocomposites.     

Adjustable surface plasmon resonance with Au,Ag, and Ag@Au core-shell nanoparticles

We report an experimental study on the synthesis of metal nanoparticles （NPs） with adjustable optical density based on surface plasmon resonance （SPR）. Metal NPs prepared by laser ablation in liquid method and the effect of laser parameters on the size, distribution, wavelength of SPR of Ag, Au, and mixture of Ag-Au, and Ag core/Au shell NPs are investigated. Our results show that the adjustable SPR band can be achieved in each class of NPs which is suitable for adjustable optical window applications.     

Modelling of sensitivity of plasmon sensory elements based on silver nanoparticles obtained by laser evaporation and ablation

A comparison of the sensitivity of the spectral position of plasmon resonance calculated by numerical methods to a change in the refractive index of the environment for ellipsoidal and spherical silver nanoparticles with a dielectric shell synthesized by laser ablation has been performed. It has been shown that sensitivity is higher for nanoparticles with the shape of a prolate ellipsoid than for spherical nanoparticles. The modeling has shown that the optimal thickness of the dielectric shell should be 10–12 nm and its refractive index should be 1.6. With this, a sensitivity of the plasmon sensor of 32 nm/RIU (RIU is refractive index unit) may be provided.     

Mie谐振耦合的亚波长金属孔宽带高透射传输

表面等离激元共振激发的亚波长金属孔透射较Bethe理论有大幅度的提高,然而,由于共振对频率的敏感性以及金属在光频的高损耗特性,表面等离激元共振难以实现亚波长金属孔的宽带高透射传输.本文采用放置在金属孔两边的硅纳米颗粒的Mie谐振耦合取代表面等离激元共振,实现亚波长金属孔的宽带高透射传输.全波仿真结果表明,采用Mie谐振耦合的亚波长金属孔(r/λ=0.1)光传输,透射系数超过90%的带宽达到65 nm,与表面等离激元共振诱导的透射增强相比,峰值增高了1.5倍,3 dB带宽拓宽了17倍.根据耦合模理论,建立了Mie谐振耦合亚波长金属孔透射的等效电路模型,并在临界耦合状态下反演出电路模型中的元件参数值.进一步研究发现,仅通过改变等效电路模型中的耦合系数,就可全面揭示Mie谐振耦合亚波长金属孔透射的传输规律,并得到与全波电磁仿真完全一致的结果,从而找到光与放置硅纳米颗粒的亚波长金属孔相互作用的数学表达,也给予人们在光学领域按照电路设计方法构建相应功能模块的启示.     

Enhanced optical transmission through an array of compound unit with multiple concentric or eccentric annular apertures

In this paper, transmission properties through an array of compound unit with multiple concentric or eccentric annular apertures are numerically studied. It is demonstrated that the transmission of the compound structure is not a simple superposition of that of each annular aperture array but exhibit substantial changes in both the position and intensity of resonant peaks. It is also found that the gap plasmon resonance exhibit split peaks when the symmetry is broken, which can be well explained from the view of charge oscillation. These properties provide a method to achieve enhanced transmission in multi-frequencies simultaneously and are of significant applicable value to the design of tunable optical devices.     

Light transmission properties of double-overlapped annular apertures

We investigate the light transmission properties of double-overlapped annular apertures in a silver film with the three-dimensional finite-difference time-domain method. It has been found that the transmission peaks are attributed to the localized surface plasmon resonance (LSPR) of nanocavities and the surface plasmon polaritons (SPPs) of the nanoparticles. The peaks of the LSPR are blueshifted when the overlapping distance is increased. Moreover, a Fano-type resonance appears in the transmitted spectral response with an appropriate overlapping distance, which is elucidated as the hybridization results of the SPPs of the nanoparticles. The number and position of the Fano resonance can be tuned through varying the overlapping distance and other geometric parameters.     

Tuning the number of plasmon band in silver ellipsoidal nanoshell: refractive index sensing based on plasmon blending and splitting

Because of the geometric features of both rod and shell, dielectric-silver core–shell ellipsoidal nanostructure with 12–40 nm semi-major axis may bring forth four surface plasmon resonance (SPR) absorption peaks at most. Theoretical calculations based on quasi-static approximation show that there is surrounding refractive index-dependent plasmon blending and splitting in the absorption spectra, which makes the number of plasmon band of the silver ellipsoidal nanoshell is tunable. The sensitivity of the plasmon blending and splitting to the surrounding refractive index may be improved by increasing the shell thickness, aspect ratio or core refractive index. This local refractive index dependent-plasmon blending and splitting presents a new sensing picture based on tuning the number of SPR absorption peaks.     

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