表面等离子阵列结构中的耦合增强反射效应及其红外光谱增强特性

使用聚焦离子束刻蚀的方法制备了不同间距的表面等离子结构阵列,研究了由方形和圆形所构成的阵列在不同间距下的光学反应.实验表明,粒子之间耦合效应随着间距的显著减小而逐渐变强,从弱耦合变化为强耦合状态.当间距小于30 nm时,发现耦合增强的反射效应,共振波长也会随着间距的减小而发生红移.将制备的超小间距纳米阵列和傅里叶变换光谱仪的ATR附件相耦合,实验验证了相关阵列结构在红外光谱增强方面的显著效果.相关的发现和表面等离子阵列结构可以在传感、探测和光谱增强等方面取得一定的应用.     

纳米金修饰碳纳米管阵列结构的表面增强拉曼散射

研究了纳米金粒子修饰碳纳米管阵列结构的表面增强拉曼散射性能.通过FDTD理论模拟仿真了不同粒径纳米金颗粒的场强分布;并采用化学还原的方法制备出直径分别为20、40和60 nm三种不同粒径的金颗粒,然后将纳米金粒子修饰到有序定向的碳纳米管阵列表面,并将该结构作为表面增强拉曼基底.FDTD软件仿真结果表明,60 nm粒径的纳米金颗粒周围场强分布最强,是入射场场强的15倍.同时将罗丹明6G溶液用于测试几组不同尺寸的金颗粒对拉曼散射光强的影响,发现60 nm金颗粒对R6G拉曼信号增强最大.FDTD理论模拟仿真和罗丹明6G溶液实验测试结果表明:金颗粒尺寸在20～60 nm内,颗粒尺寸越大,拉曼散射光的光强越大.     

基于局域表面等离激元Ag/金刚石纳米结构增强NV色心的荧光

在纳米光子学中,提高量子点的荧光强度是一个需要迫切解决的难题,现如今金属纳米材料是一种很有前途的荧光增强材料。通过Ag纳米结构的局域表面等离激元效应提高金刚石氮空位(NV)色心的荧光强度,制备了不同的Ag纳米结构(Ag纳米柱阵列和Ag纳米层),探究其对NV色心的荧光增强效果。结果表明,Ag纳米柱阵列结构的加入可将金刚石NV色心的荧光强度增强2.30倍,Ag纳米层结构的加入可将其增强1.54倍。并且,采用时域有限差分(FDTD)法分析激发和发射两个过程发现,金刚石NV色心的荧光强度随着Ag纳米结构的加入显著提高,由此验证了实验中Ag纳米结构对金刚石NV色心荧光增强的效果。此研究结果为后续进行量子点光致发光器件的设计提供了一定的参考。     

纳米银基底表面增强拉曼散射效应仿真及优化

为了更大发挥拉曼光谱在生物检测及传感领域中的作用,表面增强拉曼散射中信号增强与基底复用之间平衡优化需求一直在激励着新型基底的发展。通过用有限元方法对不同银纳米结构（不同尺寸、不同大小、不同结构）基底的表面增强拉曼散射效应进行设计优化。对三种常见结构基底进行仿真,并对结果进行对比分析,表明仿真结果与已发表的相似基底实验结果一致。     

液晶的表面增强拉曼散射

应用表面增强拉曼散射(SERS)技术,对液晶5CB分子在银、金纳米粗糙电极表面的取向进行研究.结果表明液晶5CB分子在银、金电极表面具有不同的取向,揭示了液晶5CB分子与银和金的表面原子之间的相互作用是不一样的,说明了液晶在基体表面的取向是由液晶分子与基体表面原子的相互作用导致的.对液晶5CB的表面增强拉曼光谱的实验特性、应用及其机理作了较全面的研究,并给出了如何应用表面增强拉曼光谱来确定液晶分子在基体表面的取向.在对实验结果进行分析的基础上,得出了5CB在银电极表面成近似垂直取向,而在金电极表面成较复杂取向的结果.     

双层花瓣结构光学天线表面增强红外吸收特性研究

设计了一种可用于中红外波段探测的双层花瓣结构光学天线，利用有限时域差分方法，分析了结构参数、入射光偏振方向对单层天线共振波长及尖端电场强度的影响。在优化单层结构的基础上，计算了双层天线层间距（h）介于0.1～0.8μm时，不同入射波长下上层天线尖端电场强度与入射光电场强度比值。为研究下层天线对于上层天线电场的增强机理，固定入射光波长，扩大天线层间距h (0.1～3.6μm)，对有无上层天线两种结构，分析相同探测点电场强度比随h的变化。结果表明，h<1μm时，上层天线尖端电场增强主要来自于双层天线耦合增强，其中h<0.2μm时，上层天线尖端场强随着距离h的减小而降低，主要因为近场耦合导致上层天线尖端能量转移到层间；h>1μm时，上层天线尖端电场增强主要来自于下层天线反射光的干涉增强。     

表面增强喇曼光谱的Au@SiO2核壳纳米粒子制备北大核心

研究了核壳纳米颗粒的表面增强喇曼光谱（SERS）,并制备了不同SiO2厚度的Au@SiO2核壳纳米粒子进行喇曼光谱分析测试。首先,采用化学还原法制备出酒红色的金溶胶溶液。接着,添加不同量的正硅酸四乙酯（TEOS）制备了以Au为核、不同厚度SiO2为壳包裹的Au@SiO2核壳纳米粒子。然后,采用紫外-可见光（UV-Vis）和扫描电子显微镜（SEM）对Au@SiO2核壳纳米粒子的结构进行表征。最后,不同SiO2厚度的Au@SiO2核壳纳米粒子和未进行表面修饰的金溶胶溶液中滴入等量质量浓度为0.1 mg/L的罗丹明B,离心干燥后用喇曼光谱仪测试表面增强喇曼光谱效应。结果表明：罗丹明B的检出限可达到2.1×10^-7 mol/L,在扫描范围为300-1 800 cm^-1,激发波长为532 nm的条件下,SERS活性随TEOS用量的增加先增大后减小。TEOS的用量为120μL时,罗丹明B的表面喇曼增强效应最佳。     

具有分形结构Ag纳米衬底的荧光增强效应

利用电化学沉积方法,制备出具有分形结构的Ag纳米荧光增强衬底。实验中,采用532nm连续光激发居于Ag纳米结构衬底表面附近的罗丹明6G(Rh6G)荧光分子,结果表明,具有分形结构的Ag纳米金属衬底对沉积在其表面的Rh6G分子表现出明显的荧光增强效应。根据局域场增强理论对所得实验结果进行分析,经过电化学方法制备出的分形Ag纳米结构,在外电磁场激发下能够形成较强的局域电磁场分布,从而有效地激发Rh6G荧光分子,增强其荧光辐射强度。     

自组装法制备Au纳米结构衬底及其表面增强荧光效应研究

采用自组装方法,在(APS)分子修饰后的玻璃衬底 表面,制备得 到Au纳米结构衬底。采取激光光谱学方法,研究所制备衬底对沉积其表面的Rhodamine 6G(R h6G) 分子的荧光辐射增强效应。实验发现,利用自组装方法制备的Au纳米结构衬底具有较强的荧 光增 强特性。理论分析表明,制备的Au纳米结构在外光场激发下,所形成的强局部电磁场分布 能够有效提升探针分子的电子跃迁速率,从而实现增强荧光效应。     

铜岛膜上吸附物的表面增强红外吸收光谱研究

通过置换反应在金属铝表面制备了表面没有任何保护剂且具有红外增强作用的铜岛膜,用扫描电子显微镜(SEM)、X射线衍射(XRD)和表面增强红外光谱对其形貌和性质进行表征。结果表明:铝片上沉积出的铜呈岛状结构,铜岛膜由二次铜粒子和一次铜粒子通过密堆积的方式构成;首次发现具有这种特殊结构的铜对吸附于其表面的有机分子的红外吸收光谱有较大的增强作用,使得表面增强红外光谱可以用于痕量分析、检测。     

Plasmonic Crystals: A Platform to Catalog Resonances from Ultraviolet to Near‐Infrared Wavelengths in a Plasmonic Library

Surface plasmons are responsible for a variety of phenomena, including nanoscale optical focusing, negative refraction, and surface‐enhanced Raman scattering. Their characteristic evanescent electromagnetic fields offer opportunities for sub‐diffraction imaging, optical cloaking, and label‐free molecular sensing. The selection of materials for such applications, however, has been traditionally limited to the noble metals Au and Ag because there has been no side‐by‐side comparison of other materials. This feature article describes recent progress on manipulating surface plasmons from ultraviolet to near‐infrared wavelengths using plasmonic crystals made from 2D nanopyramidal arrays. A library of plasmon resonances is constructed in the form of dispersion diagrams for a series of unconventional and new composite plasmonic materials. These resonances are tuned by controlling both intrinsic factors (unit cell shape, materials type) and extrinsic factors (excitation conditions, dielectric environment). Finally, plasmonic crystals with reduced lattice symmetries are fabricated as another means to tailor resonances for broadband coupling.     

Finite Element Analysis of Lossless Propagation in Surface Plasmon Polariton Waveguides With Nanoscale Spot-Sizes

We present simulation results on the propagation characteristics of active plasmonic waveguides at 1.55 mum wavelength based on semiconductors as the active gain media. Three waveguide structures were investigated: metal rib, metal-semiconductor-metal (MSM), and triangular metal groove. In all three structures, we observed strong plasmon mode confinement with nanoscale spot-sizes and corresponding simulated gain values compatible with existing semiconductor technology. We show the effect of systematic modification of waveguide geometry on the required gain for achieving lossless propagation in all the three plasmonic waveguide structures. We demonstrate that lossless propagation with subwavelength spot sizes well below the diffraction limit of light can be obtained by controlling the geometrical parameters of the proposed waveguides.     

Multilayer Graphene with a Rippled Structure as a Spacer for Improving Plasmonic Coupling

The plasmonic coupling, the enhanced electromagnetic field occurring through a uniform and small separation between metallic particles, is required for better application to localized surface plasmon resonance. Graphene has been studied as a good spacer candidate because of its precise controllability at subnanoscale. Here, the enhancement of plasmonic coupling among metallic nanoparticles (NPs) uniformly spread out on both sides of a graphene spacer is experimentally and simulatively investigated. Additionally, the post‐evaporated flat structure is rippled along one direction to reduce the separation between nanoparticles. As the amount of rippling increases, the enhancement factor (EF) of the plasmonic coupling increases almost linearly or quadratically depending on the size of nanoparticles. Such a highly rippled nanostructure is believed to not only increase the plasmonic coupling in either side of the spacer but lead to a higher density of “hot spots” through the spacer gap also. The observed EFs of a structure with the MLG spacer are consistent with the simulation results obtained from the classical electrodynamics. On the other hand, the SLG case appears to be inconsistent with such a classical approach, indicating that the plasmon tunneling through the thin barrier is prevalent in the case of the SLG spacer.     

Plasmonic Modulation of Valleytronic Emission in Two-Dimensional Transition Metal Dichalcogenides

Monolayered transition metal dichalcogenides (TMDs) are one kind of hexagonal 2D semiconductors with a direct bandgap structure. Due to the property of natural broken inversion symmetry in the lattice, the strong spin–orbit coupling of electrons in TMDs can induce degenerate levels with antiparallel spins in K and K′ valleys, which selectively respond with external light excitations. Surface plasmon resonance with efficient electromagnetic enhancement and near-field coupling provides excellent potential opportunities to modulate valley emission of TMDs. Efforts have been devoted to investigating the interaction principles and applications of this research field. This review focuses on plasmonic modulation of valleytronic emission in TMDs with surface plasmon polaritons (SPP) and localized surface plasmons (LSP) based on different modulation principles, respectively, and discusses possible research directions for future device applications.     

Plasmomechanical Systems: Principles and Applications

Extreme confinement of electromagnetic waves and mechanical displacement fields to nanometer dimensions through plasmonic nanostructures offers unprecedented opportunities for greatly enhanced interaction strength, increased bandwidth, lower power consumption, chip-scale fabrication, and efficient actuation of mechanical systems at the nanoscale. Conversely, coupling mechanical oscillators to plasmonic nanostructures introduces mechanical degrees of freedom to otherwise static plasmonic structures thus giving rise to the generation of extremely large resonance shifts even for minor position changes. This nanoscale marriage of plasmonics and mechanics has led to the emergence of a new field of study called plasmomechanics that explores the fundamental principles underneath the coupling between light and plasmomechanical nanoresonators. In this review, both the fundamental concepts and applications of plasmomechanics as an emerging field of study are discussed. After an overview of the basic principles of plasmomechanics, the active tuning mechanisms of plasmonic nano-mechanical systems are extensively analyzed. Moreover, the recent developments on the practical implications of plasmomechanic systems for such applications as biosensing and infrared detection are highlighted. Finally, an outlook on the implications of the plasmomechanical nanosystems for development of point-of-care diagnostic devices that can help early and rapid detection of fatal diseases are forwarded.     

利用亚趋附深度Ag膜在双层金属孔径阵列中实现一个显着的透射增强

本文采用理论和实验研究了利用亚趋附深度Ag膜在(Ag@Au)双层金属孔径阵列中实现的一个显着的透射增强现象,这是由于通过倏逝波使银/金界面中的表面等离激元（SPP）耦合作用的结果。结果表明,增强透射率是高度依赖Ag膜的厚度。当Ag膜厚度的增加,透射率峰值先增大,然后减小。此外,其他金属材料的性能也进行了讨论。当Ag膜的厚度为4 nm时,得到一个最高的透射率峰值。时域有限差分法（FDTD）模拟与实验结果吻合良好。这一发现提供了一种有效的方式来控制双层金属孔阵列的增强透射特性,在设计一个高性能的等离子体热发射器方面具有潜在的应用价值。     

具有高模场限制的异质纳米棒结构波导(英文)

现代光学及纳米光学的一个主要发展趋势是从理论和实验两方面探究用于突破传统衍射极限的亚波长级别的电磁波波导结构。表面等离子激源提供了解决此问题的有效突破口。文中根据异质波导结构的耦合以及锲型波导的表面等离子激发理论,提出了异质纳米棒结构波导,该结构具有非常高的模场限制能力,对其传输的模式理论上可实现亚波长级别的限制能力。文中主要对此结构进行了数值仿真,分析了该波导结构的能量以及传输损耗,其结果表明该结构的模场限制能力可达到衍射极限的1/500,而且通过调整结构参数,将模场的传输距离延长到毫米级别。     

Real‐Time Probing Nanopore‐in‐Nanogap Plasmonic Coupling Effect on Silver Supercrystals with Surface‐Enhanced Raman Spectroscopy

Nanopore structures have displayed attractive prospects in diverse important applications such as nanopore‐based biosensors and enhanced spectroscopy. However, on the one hand, the fabrication techniques to obtain sub‐10 nm sized nanopores so far is very limited. On the other hand, the electromagnetic enhancement of nanopores is still relatively low. In this work, using a facile chemical etching strategy on 2D plasmonic Ag nanoparticle supercrystals, fine nanopore arrays with sub‐10 nm pore size have been successfully fabricated and a “nanopore‐in‐nanogap” hybrid plasmon mode has been investigated. An in situ etching and surface‐enhanced Raman spectroscopy (SERS) detection indicate that novel hybrid plasmon structure may create an enhanced electromagnetic coupling and increase SERS signal at ≈10× magnification. The breaking of plasmon bonding dipolar mode and generation of antibonding‐like plasmon mode contribute to this enhanced electromagnetic coupling. The facile etching strategy, as a common approach, may open the doors for the fabrication of nanopores in various compositions for numerous applications.     

Manipulable and Hybridized,Ultralow‐Threshold Lasing in a Plasmonic Laser Using Elliptical InGaN/GaN Nanorods

Manipulating stimulated‐emission light in nanophotonic devices on scales smaller than their emission wavelengths to meet the requirements for optoelectronic integrations is a challenging but important step. Surface plasmon polaritons (SPPs) are one of the most promising candidates for sub‐wavelength optical confinement. In this study, based on the principle of surface plasmon amplification by the stimulated emission of radiation (SPASER), III‐Nitride‐based plasmonic nanolaser with hybrid metal–oxide–semiconductor (MOS) structures is designed. Using geometrically elliptical nanostructures fabricated by nanoimprint lithography, elliptical nanolasers able to demonstrate single‐mode and multimode lasing with an optical pumping power density as low as 0.3 kW cm^?2 at room temperature and a quality Q factor of up to 123 at a wavelength of ≈490 nm are achieved. The ultralow lasing threshold is attributed to the SPP‐coupling‐induced strong electric‐field‐confinement in the elliptical MOS structures. In accordance with the theoretical and experimental results, the size and shape of the nanorod are the keys for manipulating hybridization of the plasmonic and photonic lasing modes in the SPASER. This finding provides innovative insight that will contribute to realizing a new generation of optoelectronic and information devices.     

Coupling Analysis of GaAs-Based Microdisk Lasers With Different External Claddings

In this paper, we analyze the coupling of light from a GaAs microdisk laser into a waveguide. Starting from an air cladding, we examine several configurations to couple light into the waveguide with different cladding structures aimed to foster light coupling into the waveguide: photonic crystal and metallic (plasmonic cladding). In these coupling schemes, we tried to optimize the coupling of the emitted light into the waveguide, while maintaining a reasonable quality factor to allow the lasing operation of the device. We show that a plasmonic layer, introduced beside the waveguide can lead to a significant improvement in the coupling efficiency, reaching an efficiency close to 80%.