金属-介质光栅结构表面等离子体耦合效率的模拟研究

表面等离子体可以将光子局域在金属表面附近, 并形成很强的近场能量密度, 可以大大提高金属表面附近分子的发光效率和光电转换吸收材料的利用率, 从而提高发光器件和光电转换器件的效率. 本文研究了在一维周期性金属-介质混合结构的光栅中表面等离子体激元的耦合条件, 给出了耦合效率随着结构和填充因子的变化, 并证明了在光栅的填充因子较高以至光栅的金属间隔较小时, 光子耦合成为表面等离子体的效率较高, 可以达到94%以上. 关键词： 表面等离子体激元 填充因子 光栅 吸收光谱     

金属光栅的非对称透射现象研究

提出一种利用表面等离子体耦合的金属光栅结构,该光栅结构因入射光的方向和耦合表面等离子体的条件不同,从不同方向入射时会有不同的透射率。周期为500 nm、填充因子为0.7的Au-SiO₂光栅结构在565~589 nm波段具有单向透射性。当填充因子为0.662时,最大透射对比率达3×10⁴。当光栅厚度为60 nm时,入射波长在570~630 nm之间的透射对比率均可达到5以上,最高透射率为43%。当光栅周期为1 100 nm时,1 530~1 590 nm波段的透射对比率均大于5,可以满足中红外波段的应用。     

Effective absorption enhancement in small molecule organic solar cells using trapezoid gratings

We demonstrate that the optical absorption is enhanced in small molecule organic solar cells by using a trapezoid grating structure. The enhanced absorption is mainly attributed to both waveguide modes and surface plasmon modes, which is simulated by using finite-difference time-domain method. The simulated results show that the surface plasmon along the semitransparent metallic Ag anode is excited by introducing the periodical trapezoid gratings, which induce the increase of high intensity field in the donor layer. Meanwhile, the waveguide modes result in a high intensity field in acceptor layer. The increase of field improves the absorption of organic solar cells significantly, which is demonstrated by simulating the electrical properties. The simulated results also show that the short-circuit current is increased by 31% in an optimized device, which is supported by the experimental measurement. Experimental result shows that the power conversion efficiency of the grating sample is increased by 7.7%.     

一维金属光栅的光学反射吸收

利用RCWA(rigid coupled-wave analysis)方法研究了一维金属光栅的反射特性,考察了 瑞利反常、表面等离激元驻波共振和几何共振三种共振吸收机理,分析了这三种机理的相互作用,如表面等离激元驻波共振和几何共振可以形成混合模式. 在反射式复合金属光栅中,确认了第四种共振形式,即相位共振. 数值计算表明相位共振对光学吸收的影响有两种形式: 当光栅周期大于一个波长时,相位共振导致尖锐的吸收峰,峰位在几何共振吸收峰一侧;当光栅周期小于一个波长时,相位共振导致混合模式的共振吸收峰发生劈裂. 对一维金属光栅反射特性的研究增加了对金属光栅共振吸收模式及其相互作用的认识. 关键词： 一维金属光栅 瑞利反常 表面等离激元 相位共振     

不同预淀积层银膜表面等离子激元波的辐射效率

测量了棱镜／ＬＢ膜／银膜／空气，棱镜／银膜／空气，棱镜／银膜／空气三种结构在衰减全反射条件下激发的表面等离子激元波由于银膜－空气界面粗糙度而散射以空气中的辐射效率，同时，由散射光强分布计算出表面度粗糙度参数随横向相关长度σ和表面波纹深度δ，再由σ和δ计算出理论辐射效率，理论与实验结果相符合。     

提高OLED光导出效率的异形金属光栅的设计与优化

提出一种用于有机电致发光器件(OLED)的双面对称矩形金属光栅电极,采用时域有限差分方法(FDTD)模拟研究了OLED中表面等离子体激元的激发和耦合传输的物理规律和物理机制,详细计算和分析了该光栅结构的周期、槽宽、光栅高度、槽底厚度、入射光的入射角与电极透射效率的关系,并由此优化了结构的几何参数,使金属电极的光导出效率相对于通常的金属银层电极增强了1.77倍,为基于表面等离子体激元的高效光导出器件的优化设计提供了理论依据。     

复合金属光栅模式分离与高性能气体传感器应用

为实现近红外波段表面等离子体共振(SPR)模式的分裂和移动, 同时提高光栅基SPR传感器的品质因数, 提出了一种由双金属光栅构成的新型复合结构光栅, 并研究了其气体传感特性. 运用有限时域差分算法对该结构进行了数值模拟, 发现由复合金属光栅激发的SPR出现模式分裂的现象. 通过增大双金属光栅阵列间的相对位移改变原结构的对称性, 导致复合金属光栅分裂的SPR模式朝相反方向移动. 当相对位移量进一步增大到双光栅合并成新的单一光栅时, 随光栅结构对称性的恢复, 分裂的两共振模式最后又重新合并为一个模式. 如果待测物的折射率为1.01≤n_a≤1.05, 当相对位移量为0时, 基于复合光栅结构气体传感器的折射率灵敏度为1207.5 nm/RIU, 且品质因数达到1290.7; 当相对位移量为100 nm时, 与双共振模式对应的折射率灵敏度分别为1205.0 nm/RIU和1210.0 nm/RIU, 品质因数分别为1295.4和762.3. 因此, 复合光栅SPR传感器具有超高品质因数的性能, 使得它在生物化学传感领域中有巨大的应用潜力.     

基于表面等离子体共振增强的硅基锗金属-半导体-金属光电探测器的设计研究

金属-半导体-金属光电探测器的光栅结构可激发表面等离子体, 有效增强探测器的吸收. 为深入研究器件结构对于表面等离子体的激发及共振增强的影响, 本文提出了一种具有超薄有源层的硅基锗金属-半导体-金属光电探测器的设计方法. 采用时域有限差分的方法详细分析了光栅周期、光栅厚度、 光栅间距及有源层厚度对于表面等离子体共振增强器件性能的影响, 通过仿真模拟获得了器件的最佳结构, 详细地分析了各个界面激发的表面等离子体及其共振模式对于光谱吸收增强的机理. 仿真结果表明, 有源层锗的厚度为400nm的超薄器件在通信波段具有较高的吸收, 尤其在1550nm波长处器件的归一化的光谱吸收率可以高达53.77%, 增强因子达7.22倍. 利用共振效应能够极大地提高高速器件的光电响应, 为解决光电探测器响应度与响应速度之间的相互制约关系提供了有效途径. 关键词： 表面等离子体 锗探测器 时域有限差分仿真     

金属光栅对表面等离子体波的辐射抑制研究

对金属光栅进行严格耦合波理论计算, 得到了780和1500 nm波长入射光条件下不同光栅调制深度(20-80 nm)对应的反射谱. 根据Fano理论推导了描述反射谱线的经验公式, 最后应用有限元法计算光栅表面近场电场分布, 验证了公式的正确性. 反射谱线公式反映出光栅耦合表面等离子体的各个物理效应, 其中最重要的是反映出光栅在某一调制深度下对表面等离子体反耦合的抑制作用, 这一发现为设计光栅能量约束器件提供了物理依据.     

Extraordinary optical transmission through metal gratings with single and double grooved surfaces

We investigate the transmission properties of a normally incident TM plane wave through metal films with periodic parabolic-shaped grooves on single and double surfaces using the finite-difference-time-domain method. Nearly zero transmission efficiency is found at wavelengths corresponding to surface plasmon excitation on a flat surface in the case where the single surface is grooved. Meanwhile, resonant excitation of surface plasmon polariton (SPP) Bloch modes leads to a strong transmission peak at slightly larger wavelengths. When the grating is grooved on double surfaces, the transmission enhancement can be dramatically improved due to the resonant tunnelling between SPP Bloch modes.     

Dielectric loaded surface plasmon polariton properties of the Al_2O_3–Al nanostructure

Surface plasmons(SPs) in ultraviolet(UV) have attracted a great deal of attention because of their emerging applications in energy resources, environmental protection, and biotechnology. In this article, the dielectric loaded surface plasmon polariton(DLSPP) properties of the Al_2O_3–Al nanostructure are investigated theoretically. Sharp SP responses can be obtained in deep UV by setting an insulator grating on the aluminum film. It is found that the height of the grating element,the lattice parameter, and the filling factor can all modulate the DLSPPs of the Al_2O_3–Al nanostructure. We further find that this structure is sensitive to the embedding medium and can serve as a refractive index sensor in the UV region. The corresponding sensitivity increases with the decrease of the filling factor. The Al_2O_3–Al nanostructure may be useful for medical diagnostics and biotechnology in deep UV.     

Influence of groove depth and surface profile on fluorescence enhancement by grating-coupled surface plasmon resonance

The fluorescence intensity of a sample placed on a metal grating pattern is enhanced due to excitation by the electric field of the grating-coupled surface plasmon resonance (GC-SPR). The dependence of the enhancement on groove depth and surface profile was studied with the aim of improving the sensitivity of fluorescence detection. The enhancement was found to depend on the groove depth, with intensity most enhanced on grating substrate of about 20 nm depth, which produced an intensity about 30 times greater than that on a flat borosilicate glass substrate. Rigorous coupled wave analysis calculation showed that the shape of the groove influenced GC-SPR, suggesting that controlling not only the depth but also the shape of the grating surface profile can be an important factor in improving the sensitivity of detection by fluorescence microscopy.     

Plasmon resonances in deep nanogrooves of reflective metal gratings

Metallic gratings with very deep and narrow grooves are fabricated and their reflection spectra are characterized, which explicitly show high-order standing-wave-like resonances of surface plasmons in the cavity of nanogrooves. The effect of in-plane surface plasmon resonance is also observed, which is shown to have only a minor role on the reflection of such gratings, unlike that for shallow gratings. Using numerical simulations, the cavity resonances and their effects on the reflection of the gratings are identified and further analyzed. As field is more enhanced in the nanogrooves under cavity resonance conditions, the enhancement is also found to be dependent on the grating period, i.e. the strongest enhancement takes place for higher-order resonance modes for smaller grating period. For gratings with shallower grooves, comparable enhancement of field is also achievable by proper design of the grating period. The study suggests that field enhancement can be realized at selective wavelengths in a wide spectrum range using cavity resonances in the deep nanogrooves of metal gratings, and the position for field-enhancement can be tuned by the depth and period of the gratings.     

用于热光伏系统的近场辐射光谱控制表面结构

为提升近场热光伏发电系统的能源转换效率和发电功率,设计了Ⅲ-Ⅴ族半导体表面的矩形光栅结构,以实现从热发射器到热光伏电池的近场辐射热流选择性调制.使用在近红外波段具有表面等离子体激元特性的掺杂氧化锌作为热发射器,在GaSb热光伏电池表面添加亚微米二维光栅结构,在近场间距下形成与表面波耦合的陷光效应,由此有选择性地增强了电池能带内的光谱辐射热流.有别于以往类似研究中常用的等效近似方法,开展了时域有限差分方法模拟,能够严格考虑周期性结构细节,结合以涨落耗散理论为基础的Langevin方法,直接计算了复杂结构参与的近场辐射传热问题,以此揭示表面结构影响近场辐射传热的物理机理.结果显示使用带表面结构的薄膜GaSb电池,可使辐射热流的光谱峰值达到同温度远场黑体辐射源情况下的2.84倍,且热流增益区集中在波长略短于电池能带的窄波段区间,适应高效率、高功率热光伏系统对辐射传热设计的要求.     

表面等离子体-微腔激元对顶入射有机薄膜太阳能电池光吸收效率的增强

为了提高顶入射有机薄膜太阳能电池(TOSCs)的光吸收效率,我们将周期性矩形光栅结构引入到TOSCs中,分析了具有光栅结构的空气/Ag_1/有源层/Ag_2/空气(IMIMI)结构理想模型中复合表面等离子激元(SPPs)与微腔模式的耦合机制。通过调节光栅周期和有源层厚度,实现了复合SPPs、微腔模式以及有机材料本征吸收3个区域的重合。由于复合SPPs与微腔模式的反交叉耦合作用形成了表面等离子体-微腔激元,其局域场增强作用有效地提高了有源层的光吸收效率,提高了近19%。     

Design of tungsten complex gratings for thermophotovoltaic radiators

The concept of a kind of complex grating based on superposition of two simple binary gratings is described for potential application as thermophotovoltaic (TPV) radiators. The grating with one-dimensional microstructured surface is relatively easy to fabricate and the predicted directional-spectral emittance exhibits apparent enhancement over simple grating structures. Specifically, the emittance of the complex grating has a wider peak in the spectral region where the quantum efficiency of TPV cells is high. This enhancement can be explained by the excitation of surface plasmon polaritons coupled with the grating microstructures. At longer wavelengths, the emittance remains low to reduce the radiative heat transfer from the radiator to the TPV cells by low-energy photons that do not produce any photocurrent. Calculations using the rigorous coupled-wave analysis demonstrate that the emittance peak is insensitive to the direction, suggesting that the proposed structure may be well suitable for TPV applications.     

基于导模共振效应提高石墨烯表面等离子体的局域特性

本文构建了一种包含石墨烯和亚波长光栅的复合结构, 借助衍射光栅的导模共振效应, 在石墨烯表面激发高局域性表面等离子体激元, 研究了石墨烯与光栅结构对表面等离子体激元局域特性的影响规律, 并借助基于有限元法的COMSOL软件, 分析了缓冲层厚度、光栅周期、载流子迁移率和费米能级对石墨烯的表面电场、品质因子Q和有效模式面积S_eff的影响. 结果表明, 石墨烯表面等离子体激元的局域性在特定的参数点获得显著提高: 当μ = 0.7 m²/(V·s)时, 品质因子达到最大值Q_max = 1793; 当p = 235 nm或E_F = 0.72 eV时, 表面电场达到了入射光的3000倍以上. 强烈的局域性导致强烈 的光-物质相互作用, 因而本文提出的复合结构可实现高灵敏度传感器和高效率的非线性光学设备, 极大地扩展了石墨烯在纳米光学领域中的应用.     

等离激元增强的石墨烯光吸收

石墨烯中等离激元具有特殊的光电性质,其和入射光的强烈耦合可以引起光吸收的增强.本文基于时域有限差分法和多体自洽场理论研究了等离激元对处于光学谐振腔中的石墨烯光吸收的影响.由于石墨烯中等离激元与入射光动量和能量不匹配而不能直接相互作用,因此石墨烯上施加了金属光栅结构.研究发现光栅结构能够对入射光进行动量补偿并且能够引起其下石墨烯中的电场强度产生很大程度增强,从而导致在该石墨烯结构中太赫兹等离激元和入射光发生强烈耦合而产生太赫兹等离极化激元,同时引起石墨烯光吸收的增强.希望本文能够加深对石墨烯光电特性的理解以及可以为基于石墨烯的太赫兹光电装置提供一定的理论依据.     

Transmission properties of periodically patterned triangular prisms

Transmission properties of plasmonic structure arrays are simulated by finite element method. The array unit is composed of two combined triangular prisms. Results reveal that several resonant modes are found in the transmission spectra, which are due to the resonance of the surface plasmon polariton in the metal slit or to the localized surface plasmon resonance of the combined prisms. The resonant wavelengths can be tuned by changing the structural parameters of the combined prisms. In addition, the resonant modes are sensitive to small refractive index changes of the surrounding media, revealing potential detection applications in nanophotonic systems.