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.     

纳米银组装结构上罗丹明B的表面增强荧光效应

采用表面自组装技术,在玻璃表面构筑银纳米粒子的二维组装结构。银纳米粒子组装结构的表面等离子共振光谱中偶极子表面等离子体共振对组装结构更为敏感而表现出较大位移。组装银纳米粒子可极大增强罗丹明B的荧光。荧光的表面增强效应主要来自银纳米粒子对荧光分子所处区域的局部电磁场增强,银纳米粒子的表面分子修饰对其表面增强效应有较大的影响。     

表面分子功能化银纳米粒子的光谱特征

通过玻片表面构筑银纳米粒子二维组装结构研究吸附分子对银粒子表面等离子体共振的影响.吸收光谱结果表明银纳米粒子表面吸附二硫代乙二酰胺分子可导致金属粒子的表面等离子体共振吸收红移,主要与金属粒子的微环境改变以及吸附分子与金属间电荷转移而导致的金属粒子内部电子密度改变有关.二硫代乙二酰胺分子通过其氨基和巯基共同吸附于金属表面.     

Improvement of plasmonic field-matter interaction by subwavelength dielectric gratings

We experimentally and theoretically investigate that detection sensitivity in surface plasmon resonance (SPR) biosensors can be significantly enhanced by employing subwavelength dielectric gratings deposited on a gold film. The enhancement originates from an improvement of field-matter interaction: enhanced evanescent field intensity at the binding region and increased surface reaction area. Using a large-area SiO₂ grating array fabricated by nanoimprint lithography, experimental sensor performance measured by parylene film coating shows that the SPR substrates combined with a dielectric grating provide a notable sensitivity improvement compared to a conventional bare gold film. We also demonstrate that plasmon field can be more confined and enhanced at the dielectric gratings with a larger width. The proposed SPR structure could potentially be useful in a variety of plasmonic applications including high-sensitivity biosensors.     

Tarnishing of silver subwavelength slit gratings and its effect on extraordinary optical transmission

We study the impact of tarnishing of silver subwavelength gratings on their optical performance. We report that in the course of months under regular laboratory conditions, the gratings undergo tarnishing very differently from plain silver films: instead of thin layer of evenly distributed silver sulfide, a random pattern of rare larger crystals is formed across the grating area. As typical of plasmonic metamaterials, the gratings appear to be very sensitive to the arising structural disorder and show a very specific modification of the optical transmittance spectra – total degradation of the Wood diffraction anomaly and attenuation of the near-infrared transmission peak. The identified ‘optical fingerprints’ of the microscopic grating contamination pave a way for prospective plasmonic sensor applications.     

Transparent chromatic electrode using the mixture of silver nanowire and silver nanoprism

In this research, we studied a chromatic transparent silver nanowire (Ag NW) electrode using a silver nanoprism (Ag NP). Ag NW and Ag NP were produced using a chemical synthesis method (polyol method) and deposited on substrate via spray method.The Ag NW electrode showed a more than 80% transmittance and no or low conductivity without high temperature annealing process. In the case of applying an annealing process, a 13 Ω/□ sheet resistance was measured.The electrode, which consisted of a mixture of Ag NW and Ag NP, showed a reduced transmittance of about 70%. However, by applying Ag NPs to a conventional bare Ag NW electrode, we were able to add a chromatic characteristic to the transparent electrode; this addition was induced by the localized surface plasmon resonance (LSPR) and the low sheet resistance, even though no annealing process was applied.     

Design of a highly sensitive surface plasmon resonance sensor using aluminum-based diffraction grating

A highly-sensitive grating-based surface plasmon resonance (SPR) sensor is proposed. The angular interrogation method has been used to study the performance of the sensor, and high sensitivity is obtained if the ?1st diffraction order is used to excite surface plasmon (SP). The sensitivity as well as the width of the SPR curves and reflective amplitude is considered for designing the sensor. Compared with the conventional gold (Au)-based or silver (Ag)-based SPR sensor, it is found that the aluminum (Al)-based sensor has the best performance. The oxidation problem of an Al-based SPR sensor has been addressed by coating it with an ultrathin gold film on the surface. Numerical simulations based on rigorous coupled wave analysis (RCWA) show that the sensitivity of the optimized sensor is 245°/RIU (degree per refractive index unit).     

Enhanced optical transmission through a nanoslit by coupling light between periodic strips and metal film

Surface plasmon resonance （SPR） is obtained by exciting the surface plasmon （SP） at the metal and dielectric interface, which can greatly enhance the extraordinary optical transmission （EOT） through a nanoslit milled in the metal film. We present a structure with a 50-nm-wide silver nanoslit for EOT by coupling light into the dielectric interlayer between periodic strips and a metal film. When the period of the metallic strips is equal to the wavelength of the SPR, the transmission efficiency of 187.6 through the nanoslit is enhanced. The metallic strip width over the nanoslit is optimized to improve transmission efficiency, and the maximal efficiency of 204.3 is achieved.     

High Sensitivity Transmission-Type SPR Sensor by Using Metallic--Dielectric Mixed Gratings

We theoretically investigate transmission-type SPR sensors with novel metallic-dielectric mixed gratings by rig- orous coupled-wave analysis （RCWA）, compared to the conventional dielectric gratings based structure. It is found that the transmittance efficiency and the full width at half-maximum （FWHM） of the transmission curve can be modulated by increasing or decreasing the metallic part. Therefore, appropriate proportion of metal part will induce enhancement factor of sensor merit. Furthermore, this novel structure will also bring enhancement of resonant angle shift, which can be explained by plasmonie interpretation based on a surface limited increase of interaction area and excitation of localized surface plasmons （LSPs）. The proposed configuration has a wide range of potential applications not only as sensor but also other optical devices.     

Negative role of surface plasmons in the transmission of metallic gratings with very narrow slits

It is generally admitted that the extraordinary transmission of metallic grating with very narrow slits is mainly due to the excitation of surface plasmons on the upper and lower interfaces of the grating. We show that the surface plasmon contribution is not the prime effect and that waveguide mode resonance and diffraction are responsible for the extraordinary transmission. Additionally and surprisingly, we reveal that the transmittance of subwavelength metallic gratings is always nearly zero for frequencies corresponding to surface plasmon excitation. This finding implies that surface plasmons play a negative role in the transmission.     

纳米银与表面吸附荧光素的荧光性能的影响

研究了纳米银粒子对表面吸附荧光素(fluorescein,Fl)的荧光性能的影响。Fl溶液中加入纳米银粒子,Fl分子包覆在纳米银粒子表面形成Fl_n-Ag复合物使纳米银相互桥连形成类似网络的结构,且Fl分子吸收峰随着纳米银浓度的增加发生红移。纳米银通过产生的强局域场将能量传输给Fl发光中心,实现了Fl的荧光增强,荧光增强效率随着纳米银浓度的增加具有最大值。较大粒径的纳米银使Fl获得最大荧光增强效率所需浓度较低且最大荧光增强效率值较高。研究结果表明,纳米银与Fl间的能量传输主要由Fl分子附近局域电磁场增强和分子到金属表面无辐射跃迁能量转移过程所决定并与纳米银的浓度、尺寸密切相关。     

功能光学纳米Ag薄膜的制备及其光学特性研究

对以热蒸发法制备的超薄Ag薄膜,扫描电子显微镜结果显示其呈纳米尺度的颗粒状,由透射谱测量发现其具有表面等离子体激元特征.检测到不同条件制备纳米Ag薄膜的表面等离子体共振吸收峰的位移规律,且纳米Ag材料具有选择性的透过、反射特性.通过不同的制备条件,得到了在长波范围内透过率超过90％、在表面等离子体共振峰值位置处反射率接近50％且峰位可调的光学薄膜材料.这种薄膜材料有望成为应用在薄膜太阳电池中间层中具有潜在性光管理功能的光学薄膜材料. 关键词： 热蒸发 纳米Ag薄膜 表面等离子体激元 光管理     

Investigation of spatial self-phase modulation of silver nanoparticles in clay suspension

We have investigated the spatial self-phase modulation (SSPM) phenomena in a clay suspension containing silver nanoparticles. Silver nanoparticles (Ag-NPs) were synthesized in the space of lamellar structure of montmorillonite (MMT) by using chemical reducing agent. The UV-vis spectra of the obtained Ag-NPs showed that the intensity surface plasmon resonance (SPR) peaks increase with increasing in concentration of AgNO₃. The results from Ag-NPs UV-vis spectra were in good agreement with the structure studies performed by TEM. The SSPM phenomena manifestation of the non-linear optical property appeared only when MMT suspension filled with Ag-NPs as shown in the existence of far-field pattern. This property increased with the increase of Ag-NPs concentration and limited to small range.     

Near-field Moiré effect mediated by surface plasmon polariton excitation

We have demonstrated a surface plasmon polariton mediated optical Moiré effect by inserting a silver slab between two subwavelength gratings. Enhancement of the evanescent fields by the surface plasmon excitations on the silver slab leads to a remarkable contrast improvement in the Moiré fringes from two subwavelength gratings. Numerical calculations, which agree very well with the experimental observation of evanescent-wave Moiré fringes, elucidate the crucial role of the surface plasmon polaritons. The near-field Moiré effect has potential applications to extend the existing Moiré techniques to subwavelength characterization of nanostructures.     

Profiling of holographic diffraction gratings by using silver-arsenic triselenide interaction

Rulings of holographic gratings were profiled by interaction of silver with chalcogenide glassy semiconductors. The shape of the rulings was determined with an atomic force microscope. Angular and spectral dependences of the diffraction efficiency of the gratings were found, and a relation between these dependences and the grating surface pattern was analyzed.     

基于塔姆激元-表面等离极化激元混合模式的单缝加凹槽纳米结构的增强透射

金属单缝纳米结构因为结构简单、易于集成,常用在基于表面等离极化激元(surface plasmon polaritons,SPPs)的纳米结构中构建光源.但是,金属亚波长单缝结构一直存在透射率低的问题,如何提高其透射率一直是研究的重点.为了更好地提高金属亚波长单缝的透射率,本文对之前文献提出的分布式布拉格反射镜(distributed bragg reflector,DBR)和金属银薄膜纳米缝结构进行改进,在金属银薄膜两侧设计凹槽.当TM偏振光由DBR侧入射至DBR-银纳米缝结构时,DBR-银膜界面上和银膜入射侧凹槽一起激发的塔姆激元(Tamm plasmon polaritons,TPPs)和SPPs,以及纳米缝和银膜出射侧凹槽对的SPPs同时激发,利用凹槽激发的SPPs和银膜表面处的TPPs-SPPs混合模式的干涉相长耦合作用,通过塔姆激元的局域场增强效应和两侧凹槽与单纳米缝的干涉相长耦合作用进一步提高了表面等离极化激元模式的激发效率,再加上纳米缝中的类法布里-珀罗腔共振效应,使纳米缝的透射率得到增强.本文采用有限元方法研究了DBR-银纳米缝结构上单纳米缝加凹槽的透射特性.经过一系列参数优化,使DBR-银纳米缝凹槽结构的最大透射率增加到0.22,相对于TiO_2-银纳米缝结构的透射率(0.01)提高了22倍,比文献[23]得到的最大透射率0.166有所提高.研究结果在纳米光源设计、光子集成电路和光学信号传输等相关领域具有一定的应用价值.     

Surface plasmon resonance sensor based on diffraction grating with high sensitivity and high resolution

A surface plasmon resonance (SPR) sensor based on diffraction grating with high sensitivity and high resolution is proposed. The sensitivity of grating coupled SPR sensor based on angular interrogation is enhanced by replacing +1st diffraction order of metallic grating with −1st diffraction order to excite the surface plasmon. To improve the resolution of grating-based SPR sensor, aluminum is used as an SPR-active metal. The reflectivity dip of the Al-based sensor is sharper than an Au-based one, which is the mostly widely used as SPR-active metal. And 3-nm-thick gold film is deposited on the grating surface in order to protect the Al layer from getting oxidized. Numerical simulations show that the sensor not only has high sensitivity and high resolution, but also exhibits good linearity.     

金膜与银膜光纤SPR传感器

不同的金属传感层对光纤SPR传感器的特性有着重要的影响.根据该传感器的理论公式,计算了金膜、银膜传感器的输出光谱,并与实验结果进行了比较.结果表明,银膜光纤SPR传感器的理论输出光谱和实验检测光谱吻合很好,而金膜吻合较差.分析了出现这种偏差的原因.     

Fluorescent silver nanoparticles via exploding wire technique

Aqueous solution containing spherical silver nanoparticles of 20–80 nm size have been generated using a newly developed novel electro-exploding wire (EEW) technique where thin silver wires have been exploded in double distilled water. Structural properties of the resulted nanoparticles have been studied by means of X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The absorption spectrum of the aqueous solution of silver nanoparticles showed the appearance of a broad surface plasmon resonance (SPR) peak centered at a wavelength of 390 nm. The theoretically generated SPR peak seems to be in good agreement with the experimental one. Strong green fluorescence emission was observed from the water-suspended silver nanoparticles excited with light of wavelengths 340, 360 and 390 nm. The fluorescence of silver nanoparticles could be due to the excitation of the surface plasmon coherent electronic motion with the small size effect and the surface effect considerations     

Sensitivity enhancement of surface plasmon resonance sensor using continuous film metallic gratings

A surface plasmon resonance (SPR) sensor based on continuous film metallic gratings is numerically investigated for enhance sensitivity. The results calculated by rigorous coupled-wave analysis (RCWA) present that interplays between localized surface plasmons and surface plasmons polaritons contribute to sensitivity enhancement. The sensitivity enhancement factor (SEF), which represents the influence of metallic grating, increased as the grating period decreased. In addition, several reflection dips can be achieved as the period of metallic grating increased. By double-dips method, the sensitivity SPR sensor based on continuous film grating-based is improved into 153.23°/RIU, which is more sensitive than conventional thin film-based SPR sensor in the same condition. The SPR sensor based on continuous film metallic gratings exhibits good linearity.