银纳米结构中的表面等离激元和Fano共振效应研究

【作者】 李媛；

【导师】 霍义萍；

【作者基本信息】 陕西师范大学 ， 光学， 2017， 硕士

【摘要】 贵金属纳米结构支持的表面等离激元能够在纳米尺度上实现对光场的有效操控,因而获得了十分广泛的关注。在贵金属纳米体系中,表面等离激元共振效应对于结构的形状和尺寸,环境的折射率,以及激发光的入射方向和偏振方向等都十分的敏感,这些性质对于其光谱调控有着十分重要的意义。表面等离激元体系中的Fano共振效应是由于金属纳米结构中亮暗模式的相消干涉所引起的。Fano共振的存在使得纳米结构体系具有更精细的光谱,更大的局域场增强。这些特性使得表面等离激元在生物传感、表面增强光谱学、表面等离激元波导、太阳能电池等领域都展示出巨大的应用前景。基于贵金属纳米结构中表面等离激元共振效应的研究现状,考虑到目前研究工作大都集中在复杂纳米体系,以及有关磁Fano共振的研究较为不足等情况,我们设计了银纳米椭球/双开口圆环结构和劈裂环-完整圆环结构,并对它们的光学特性做了系统的研究分析。本文的研究内容主要分为三个部分,各部分的具体内容如下.:第一部分介绍了几种常用的表面等离激元数值模拟计算方法,包括离散偶极近似法(DDA)、时域有限差分法(FDTD)和有限元方法(FEM)。其中有限元方法是本论文所使用的模拟计算方法,而基于有限元方法的COMSOLMultiphysics是我们所使用的模拟软件,我们对其仿真步骤和特点做了较详细的介绍。第二部分研究了银纳米椭球/双开口圆环结构的表面等离激元特性。在该结构的消光截面中出现了反绑定的偶极-偶极模式和绑定的偶极-偶极模式,当改变椭球的旋转角度时反绑定模式能够被增强或抑制。另外,椭球偏置引起对称性破缺导致结构中的Fano共振的产生,结构的Fano线型可以通过改变椭球偏置量的大小来调节。这种可调控的Fano线型使得该结构在生物传感领域拥有一定的应用价值。第三部分研究了劈裂环-完整圆环纳米结构的局域等离激元共振和局域电磁场增强等光学特性。我们设计的劈裂环-完整圆环结构可以产生电和磁Fano共振,通过改变几何参数能够对它们进行调控。我们发现,该结构体系对于垂直入射的平面波的磁Fano共振响应都具有奇数个的环形位移电流和奇数个的磁热点,相邻的两个环形电流模式具有相反的相位。另外,在磁Fano共振模式处同时具有较大的电场和磁场增强。研究表明,该结构还具有很强的折射率传感因子,所以它具有应用于传感器、表面增强光谱、低损耗磁等离激元传播和其他基于磁Fano共振的光学器件等方面的潜力。更多还原

【Abstract】 Noble metal nanostructures,which support surface plasmons,have gained extensive attention due to the ability to manipulate light at nanoscale.The surface plasmon resonant effect at noble metal nanostructures is very sensitive to the shape and size of the nanostructure,the refractive index of surrounding medium,direction and polarization of the incident light.These properties have very important significance for spectrum control.Fano resonances can be achieved by the destructive interference between the bright mode and dark mode of the plasmonic systems.Finer spectrum and stronger enhancement of local field can be observed in the systems due to the existence of Fano resonances.Therefore,surface plasmons have tremendous potential applications in biosensing,surface-enhanced spectroscopy,plasmon waveguide and solar cells.Taking the fact that current researches focus on the complex nanostructure,and the researches on magnetic Fano resonance is relatively insufficient,silver ellipsoid/double split-ring and split ring-perfect ring nanostuctures are designed.The optical properties of these structures have also been investigated systematically.This thesis has been divided into three sections.Main contents of each section are descr:ibed as follow.In the first section of this thesis,several popular calculation methods are introduced respectively,including discrete dipole approximation(DDA)method,finite difference time domain(FDTD)method and finite element method(FEM).We focus on introducing finite element method and the corresponding simulation software COMSOL Multiphysics in setting models and its characteristics.In the second section,the plasmonic properties of a silver ellipsoid/double split-ring nanostructure are investigated theoretically.Anti-bonding and bonding dipole-dipole mode are excited in the extinction cross section of the structure.The anti-bonding dipole-dipole mode can be enhanced or suppressed by adjusting of the rotation angle of the ellipsoid.With symmetry breaking introduced by moving the ellipsoid,Fano resonances can be stimulated,which can be manipulated by modifying the offset of the ellipsoid.On account of the tunable Fano spectra of this nanostructure,it has potential applications in biosensing.In the third section,the optical properties of split ring-perfect ring,including local surface plasmon resonance and enhancement of local field,is analyzed theoretically.The plasmonic system could support both electric and magnetic Fano resonances,which can be adjusted by tuning the geometrical parameters.We find that the plasmonic system responds to a normal incident plane wave mainly by exciting the magnetic Fano resonances with uneven displacement current loops and uneven magnetic hot spots,and the adjacent current loops are always anti-phase.In addition,great enhancement of electric field and magnetic field can be achieved simultaneously at magnetic Fano modes.Calculation results exhibit that this structure is sensitive to the refractive index of surrounding medium.Therefore,this nanostructure has significant potential applications in sensor,surface-enhanced spectroscope,the propagation of low-loss magnetic plasmons and other optical devices based on magnetic Fano resonance.更多还原