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摘要:金属纳米颗粒的等离激元共振引起的局域场增强效应,对显微成像、光谱学、半导体器件、非线性光学等诸多领域都具有极大的应用潜力。尤其是在光学纳米材料领域,通过亚波长金属纳米颗粒与电介质的组合引起局域场增强效应,提高了纳米材料的光学性能,并促进纳米材料在光学领域的应用。本文主要综述几种常见纳米结构所产生的局域场增强效应及其应用,详细介绍并总结了金属纳米材料的不同结构参数与局域场增强的关系及局域场增强在非线性光学、光谱学、半导体器件等领域的应用。未来,随着对金属纳米材料的研究愈发深入,局域场增强的应用将更加广泛,这将对诸多领域的发展产生重要影响。Abstract:Local field enhancement(LFE) based on the plasmon resonance characteristics of metal nanoparticles has great potential in many fields such as microscopy, spectroscopy, semiconductor devices and nonlinear optics. Especially in the field of optical nanomaterials, local field enhancement effect can be produced by the combination of sub-wavelength metal nanoparticles and dielectrics to improve the optical properties of nanomaterials and promote the application of nanomaterials in the field of optics. In this paper, the local field enhancement effect of several common nanostructures and their applications is mainly reviewed. The relationship between different structural parameters of metal nanomaterials and the local field enhancement and the application of local field enhancement in nonlinear optics, spectroscopy, semiconductor devices are introduced and summarized. It is foreseeable that in the future, as the research on metal nanomaterials progresses, the application of localized field enhancement will be more extensive, which have a significant impact on the development of many fields.
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图 6局域电场因子与插入金球的波长和半径的函数关系:(a)C点, (b)F点, (c)B点, (d)E点, (e)A点, (f)D点
Figure 6.Local electric field factor in the gold-dielectric-gold nanoshells as a function of wavelength and radius of the inserted gold sphere:(a)at point C, (b)at point F, (c)at point B, (d)at point E, (e)at point A, and (f)at point D
图 9纳米聚焦表面等离子体激元(SPP)的实验示意图
Figure 9.Experimental schemes of nanofocused surface plasmon Excitations(SPP). (a)SEM image of a gold tip with a grating coupler 20 μm away from the apex with illustration of SPP nanofocusing triggering ultrafast electron emission. (b)Corresponding electron pulse imaging setup using an ultrashort 5 fs laser system for plasmon excitation. (c)Normalized spectral power density(SPD) of the ultra-broadband spectrum of the laser system
图 10飞秒 作用尖端金涂层产生的四波混频信号成像(a)Au-Si近场FWM图像,图中“S1,S2,S3”是对应的“热点”,(b)同一时刻的原子力显微镜图像,(c)双脉冲激发,对应于τ=0 fs 8.2 fs, 16.4 fs不同脉冲间延迟下,同一位置的四波混频图像,(d)对“S1”及“S2”处四波混频强度随去相位时间变化的模拟图,(e)沿a图(蓝色)和b图(黑色)中的白色虚线提取的FWM(蓝色)信号及AFM(黑色)形貌图(彩图见电子版)
Figure 10.Femtosecond FWM nanoimaging of coherent plasmon dynamics in gold. (a)Near-field FWM image of a Si-Au step, showing 'hotspots' S1, S2and S3. (b)Simultaneously acquired AFM topography. (c)FWM images of the same region with two-pulse excitation, corresponding to an inter-pulse delay ofτ=0 fs(top), 8.2 fs(middle) and 16.4 fs(bottom), demonstrating evolution of the relative intensities in spots S1, S2and S3. (d)FWM intensity in S1and S2for the three delays, showing variation in dephasing timeT2, with simulation forT2=16 fs(black solid line) andT2=10 fs(red solid line). (e)Line profiles of FWM signal(blue), showing ~50 nm spatial resolution, and AFM topography(black), extracted from (a) and (b) along the white dashed lines(color figures see electronic version)
图 11(a) 紫外区局域场增强的“V”形纳米结构几何形状。颜色表示电场分布,箭头表示能流方向; (b)nm=2.1,f=17 nm,θ=50°,h=480 nm,a=9 nm;(c)nm=1.7,f=20 nm,θ=32°,h=560 nm,a=9 nm,“V”形槽内介质的介电常数为1
Figure 11.(a)The geometry of V-shaped nanostructure for local field enhancement in UV region. Distribution of the electric field in the resonator(color) and direction of the power flow(arrows) for two sets of parameters: (b)nm=2.1,f=17 nm,θ=50°,h=480 nm,a=9 nm; (c)nm=1.7,f=20 nm,θ=32°,h=560 nm, anda=9 nm. Dielectric constant of the medium inside the V-groove equals to 1. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article)
图 12(a)f=17 nm,a=9 nm时局域场强度|E(h,θ)|随深度h和孔径角θ的变化关系。(b)θ=50°,h=480 nm时局域场强度|E(f,a)|随金属膜厚度f和尖端圆角半径a的变化关系。电解质的折射率nm=2.1,“V”形槽内介质折射率为1
Figure 12.(a)Dependence of the local field enhancement |E(h,θ)| on depth h and aperture angleθ, forf=17 nm anda=9 nm. (b)Dependence of the local field enhancement |E(f,a)| on the thickness of the metal film f and the fillet radius a, forθ=50°,h=480 nm. Refractive index of the dielectric medium is equalnm=2.1, refractive index of the medium incide the V-groove is 1
图 13在圆偏振入射光束下的基于反射纳米棒的CGH的图示,圆偏振入射光束通过四分之一波片(QWP)落在表面上,反射光束在远场中形成全息图像
Figure 13.Illustration of the reflective nanorod-based CGH under a circularly polarized incident beam. The circularly polarized incident beam, which is converted from a linearly polarized one by passing through a quarter wave plate(QWP), falls on the metasurface. The reflected beam forms the holographic image in the far field
图 15线性超表面与入射波长的反射率(黑线)和场增强(红线)分布。红色实线和虚线分别描绘了局域场增强和空间平均场增强的相对值
Figure 15.Reflectance (black line) and field enhancement (red lines) distributions of the linear metasurface versus the incident wavelength. The red solid and dotted lines depict the local maximum and the spatially averaged field enhancement, respectively
图 16超材料的几何结构与近场处磁场和电场分布模拟图,(a)磁共振成像装置切割示意图,(b)发射(外部)和多元件接收线圈阵列(内部)的体内实验的照片,(c)高介电常数电介质基片(左)与其金属结构(右)组成的超表面结构,(d)数值计算出的磁(左)和电(右)场在超表面附近的映射(显示为蓝色矩形)
Figure 16.Structural geometry of the metamaterial and simulation diagram of near field magnetic and electric field distributions. (a)Schematic of the MRI setup with a cut-out for better visualization of the setup. (b)A photograph of the in-vivo experiment including the transmit(outer) and multi-element receive coil array(inner). (c)Artist's view of the hybrid metasurface, including high permittivity dielectric substrate(left) combined with its metallic structure(right). (d)Numerically calculated magnetic(left) and electric(right) field maps in vacuum near the metasurfaces(shown as a blue rectangle)
图 20金属-蓝宝石纳米结构产生高次谐波示意图,(a)用于产生极紫外和光谱测量的实验装置,(b)通过测量极紫外光谱得到高次谐波(HHG)峰,(c)FDTD模拟入射 场与蓝宝石尖端增强场的时间曲线,(d)HHG峰的归一化曲线,带宽表示每个峰值的光子能量除以其谐波阶次。FWHM:半峰宽
Figure 20.High-harmonic generation from the metal-sapphire nanostructure. (a)Overall hardware configuration for extreme ultraviolet generation and spectrum measurement. (b)Measured extreme ultraviolet spectra showing HHG peaks. (c)FDTD-simulated temporal profile of the enhanced field at the sapphire tip for the incident laser field. (d)Normalized profiles of measured HHG peaks. The bandwidth represents the photon energy spread of each peak divided by its harmonic order. FWHM: full-width at half-maximum
表 1有无AuNRs@SiO2的器件光伏参数
Table 1.Photovoltaic parameters for devices with and without AuNRs@SiO2
SiO2thickness/nm Voc/V Jsc/(mA·cm-2) FF PCE/% Rs/(Ω·cm2) Rsh/(Ω·cm2) ref. 0.74 16.5 0.60 7.52 10.1 801 3±0.6 0.74 21.2 0.60 9.55 7.4 923 14±2 0.74 19.1 0.60 8.53 8.7 322 38±5 0.74 18.5 0.60 8.25 7.8 435 -
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