固/固型二维正方晶格声子晶体缺陷态研究*

固/固型声子晶体在抑制噪音和隔离振动等工程领域有着潜在的应用。利用有限元方法对存在缺陷的二维正方晶格金/环氧树脂声子晶体进行了研究,数值计算结果表明弹性波在点缺陷处局域,带隙中出现多条缺陷模,点缺陷数目的增加对声子晶体局域特性产生显著影响;弹性波沿着线缺陷传播形成波导,改变线缺陷结构可以改变弹性波传播方向和实现信号的分离。对声子晶体缺陷特性的研究可为声学滤波器和波导等器件的设计提供参考。     

缺陷态对4340钢-环氧树脂二维声子晶体带隙的影响

采用平面波展开法及平面波超元胞法研究缺陷态对4340钢-环氧树脂二维声子晶体带隙的影响. 以环氧树脂作为基底,把正方形结构排列的4340钢均匀的插入基底中,计算完整晶体、45°线缺陷态晶体、90°线缺陷态晶体、135°线缺陷态晶体、180°线缺陷态晶体的带隙. 结果表明,缺陷态的带隙宽度与完整晶体的带隙宽度相比最大可增大约31倍;对于不同的缺陷结构在F=0.1-0.9的范围内均有带隙出现且随着缺陷态角度的增大. 同时讨论带隙数目N,最低带隙相对宽度Δω/ω_g与填充率F之间的关系. 关键词： 缺陷态 带隙宽度 带隙数目     

Band-gap guidance in optically induced photonic lattices with a negative defect

We report the first experimental demonstration of band-gap guidance of light in an optically induced two-dimensional photonic lattice with a single-site negative defect (akin to a low-index core in photonic-crystal fibers). We discuss the difference between spatial guidance at a regular and a defect site, and show that the guided beam through the defect displays fine structures such as vortex cells that arise from defect modes excited at higher band gaps. Defect modes at different wavelengths are also observed.     

Frequency modulation of waveguides in acoustic band-gap materials consisting of solid cylinders in viscous liquid

We investigated waveguides in acoustic band-gap materials consisting of steel cylinders in a liquid with viscous damping. Numerical results show that when the viscous penetration depth is comparable to the structural length scale, linear defect states fall in complete acoustic band gaps forming waveguides. It is also found that the magnitude of the viscosity in the liquid has an influence on the frequency of waveguides, that large viscous damping can make the defect modes ascend. An expected frequency of waveguides can be obtained by modulating the viscous damping parameter θ.     

二维周期性复合介质中声波带隙结构及其缺陷态

用平面波展开方法和超元胞方法,研究了钢柱体在水中按周期性排列时声波的能带结构.讨论了钢柱体的横截面形状(圆形和正方形)、柱体的体积填充率及缺陷等因素对声波带隙结构的影响. 关键词： 声波 带隙 缺陷态     

二维点缺陷正方光子晶体的微腔结构

通过平面波展开法对由Al₂O₃介质棒在空气背景介质中构成含有点缺陷的二维正方光子晶体微腔结构进行研究,计算得出缺陷态能带以及缺陷态模场分布。缺陷模对应的电磁波波长为470~476nm。对该微腔结构的品质因数的求解,得出缺陷态光谱曲线。在光谱曲线中,随着传输波长的增大,将产生几个峰值,并且在475nm处的波动最为明显,反映出在475nm附近的电磁波段在缺陷处的光强较大。进一步利用全矢量等效折射率法研究该结构缺陷模频率的稳定性,得出等效折射率的变化曲线。从等效折射率变化曲线可以看出,当传输波长达到475nm时,该结构已经达到稳定传输的区域。含缺陷模的二维光子晶体微腔结构在光子晶体发光二极管以及高阈值半导体激光器等方面有着重要的应用价值。     

二维八重准晶有机光子晶体平板的光学传播特性

采用时域有限差分法研究了二维八重准晶有机光子晶体的光传输特性,重点分析了光束在聚苯乙烯空气柱平板结构和聚苯乙烯介质柱结构中的透射特性与光局域特性。研究结果表明,即使在低折射率对比度的情况下,两种完整八重准晶平板结构中均出现了可见光波段的光子带隙和本征模,且光子带隙中心位置随着平板厚度的增大而红移。当在两种准晶结构中引入缺陷微腔时,带隙内的缺陷模产生位置和波长红移特性随着微腔结构的变化规律明显不同,这种差异性是由两种物理机制(即光子晶体缺陷能级变化与微腔所支持的驻波条件)共同作用的结果。这一研究结果将为实验制备有机准晶发光器件提供一定的理论基础。     

Surface acoustic waves in 2D-phononic crystal of laminated pillars on a semi-infinite ZnO substrate

In this paper a phononic crystal of laminated pillars which are composed of two materials on a semi-infinite ZnO substrate is proposed. The unit cell can be regarded as a double-resonator model, which explicates the variation of band gaps. It is revealed that the band structure of the PC is highly influenced by the proportion of PZT-4 in laminated pillars. Besides, the high-frequency band gaps are the result of combined actions of the local resonance and the Bragg scattering, and the former dominates. Furthermore, the influences of the structural damping are investigated. It is observed that the bandgap-ratio remain unchanged and the band gaps translate to the right with isotropic structural loss factor increasing. Additionally, by introducing linear defects inside the laminated pillars, elastic energy at surface is strongly confined within defect pillars, and the coupling between defective pillars and SAW is governed by the physical parameter of resonators.     

横磁模式下二维非磁化等离子体光子晶体的线缺陷特性研究

采用等离子体的分段线性电流密度卷积时域有限差分算法研究了横磁波入射时具有单一线缺陷的二维非磁化等离子体光子晶体的缺陷模特性. 从频域角度分析得到微分高斯脉冲的透射系数,并讨论该光子晶体的晶格常数、介质圆柱半径、周期常数、缺陷层参数和等离子体参数对缺陷模特性的影响. 结果表明,改变周期常数、缺陷层位置和等离子体碰撞频率不会改变缺陷模的频率,改变缺陷层介质圆柱的相对介电常数、半径和缺陷层到介质层的中心距离可以在不改变禁带宽度的前提下实现对缺陷模的调节,改变晶格常数、介质圆柱半径和等离子体频率能同时实现对禁带宽度和缺陷模的调节. 关键词： 等离子体 光子晶体 缺陷模 时域有限差分算法     

含负折射率材料1维光子晶体的偏振无关非全向的缺陷模

运用光学传输矩阵理论,研究了含负折射率材料1维光子晶体缺陷模的偏振特性。结果显示,零均折射率带隙中缺陷模对入射角和偏振有较强的依赖。通过对缺陷层参数的优化设计,得到了一系列的偏振无关非全向缺陷模,这是传统1维光子晶体中不能出现的。应用这些缺陷模,设计了低通、高通、带通空间滤波器。与传统光子晶体空间滤波器相比,这些空间滤波器具有偏振无关的优点。     

Properties of defect modes in one-dimensional photonic crystals containing a graded defect layer

The properties of defect modes in one-dimensional photonic crystals (PCs) containing a graded defect layer are studied theoretically. The relative permittivity and magnetic permeability of the graded defect layer vary continuously along the direction perpendicular to the surface of the layer. The effect of the linear gradation profiles of the relative permittivity and permeability are studied in detail. It is shown that the defect modes appear inside the forbidden band gaps in its transmission spectra and the gradation profiles of the relative permittivity and permeability affect the defect modes significantly. By changing the gradation parameters, the intensity and position of the defect modes can be tuned. Therefore, introducing a graded defect layer in one-dimensional PCs provides possible mechanism for tuning the defect modes. This may be useful in the design of channeled filters.     

Effects of various defects on the electronic properties of single-walled carbon nanotubes: A first principle study

The geometries,formationenergies and electronic band structures of （8, 0） and （14, 0） singlewailed carbon nanotubes （SWCNTs） with various defects, inehlding vaeaney, Stone-Wales defect, and octagon pentagon pair defect, have been investigated within the framework of the density- huictional theory （DFT）, and the influence of the concentration within the same style of deflect on the physical and chenfical properties of SWCNTs is also studied. The results suggest that the existeilcc of vacancy and octagon-pentagon pair deflect both reduce the band gap, whereas the SW- defect induces a band gap opening in CNTs. More int, erestingly, the band gaps of （8, 0） and （14, 0） SWCNTs eonfigurations with two octagon pentagon pair defect presents 0.517 eV and 0.163/eV, which arc a little smaller than the perfectt CNTs. Furthermore, with the concentration of defects increasing, there is a decreasing of band ga.p making the two types of SWCNTs change from a semiconductor to a metallic conductor.     

具有缺陷模的氧化铝光子晶体的光学传感性能

采用在周期性氧化电压信号中插入恒压波形的方法成功制备了具有缺陷模的一维氧化铝光子晶体. 这种晶体的透射光谱研究表明,缺陷的厚度对缺陷模的透过率具有显著影响,当缺陷厚度在180 nm时,光子禁带内部出现透过率为55%、半峰宽约为18 nm的缺陷模. 该缺陷模能够对进入到氧化铝孔道内部的液体物质做出响应,其位置与液体的折射率线性相关.     

含双负缺陷的一维光子晶体耦合腔的杂质带特性

利用转移矩阵方法研究了含双负缺陷的一维光子晶体耦合腔的透射谱.计算结果表明，如果改变缺陷的折射率，缺陷模之间的耦合作用将发生改变，使得能隙中的杂质带也随之改变.若这个折射率取适当值，则可以在禁带中同时出现几个尖锐的透射峰和较宽的通带，这种结构可同时用于多通道窄带滤波和宽带滤波. 关键词： 光子晶体 缺陷模 杂质带 滤波     

Investigation of one-dimensional photonic crystals composed of dispersive materials

One-dimensional photonic crystals (1DPCs) composed of dispersive materials (including negative refractive index materials, negative μ materials, and negative ? materials) are proposed. The dependence of the band gaps on the angle of incidence and thickness scale are investigated by using the transfer matrix method. Simulation results show that the band gaps of these dispersive material 1DPC are insensitive to the thickness scale. The defect modes of these doped 1DPCs behave specially when the thickness of the defect layer, the angle of incidence and the thickness scale of PC change.     

Influence of defect states on band gaps two-dimensional phononic crystal in the of4340 steel in an epoxy

The band structures of a new two-dimensional triangle-shaped array geometry of 4340 steel cylinders of square cross section in an epoxy resin were studied by the plane-wave expansion and supercell calculation method. The band gaps of this type of phononic crystals with different defects were calculated such as defect-free, 60 crystal linear defect states, 120 crystal linear defect states, and 180 crystal linear defect states. It was found that the band gap will emerge in different linear defects of the phononic crystals and the bandwidth of linear defect states is larger than that of the free-defect crystal by about 2.14 times within the filling fraction F = 0.1-0.85. In addition, the influence of the filling fraction on the relative width of the minimum band gap is discussed.     

光子晶体局域缺陷模及耦合特性研究

用超胞平面波展开法计算了二维正方格子介质柱光子晶体缺陷模,系统模拟了在改变缺陷模数目和缺陷模之间的距离及在不同耦合方向等情况下的耦合特性。计算结果表明：局域缺陷模之间的耦合所产生分裂的缺陷模式频率随着缺陷之间的距离而发生变化．当缺陷之间距离增加时,缺陷模之间耦合变得越来越弱且奇模和偶模交替变化;随着耦合缺陷点数目增加,缺陷模在光子带隙内形成一个缺陷带;当平面波平行于缺陷模耦合方向入射时．可以同时激发奇模和偶模．当入射平面波垂直于耦合方向时．仅产生偶模;沿对角线方向耦合的定域化的缺陷模电磁场快速衰减使得那些方向每一个单谐振腔局域光场与它邻近的谐振腔不发生耦合,其本征频率与波矢无关。     

Influence of defect states on band gaps in the two-dimensional phononic crystal of 4340 steel in an epoxy

The band structures of a new two-dimensional triangle-shaped array geometry of 4340 steel cylinders of square cross section into epoxy resin were studied by the plane-wave expansion and supercell calculation method. The band gaps of this type of phononic crystals with different defects were calculated such as defect-free, 60° crystal linear defect states, 120° crystal linear defect states, and 180° crystal linear defect states. It was found that the band gap will emerge in different linear defects of the phononic crystals and the bandwidth of linear defect states is larger than that of the free-defect crystal by about 2.14 times within the filling fraction F=0.1-0.85. In addition, the influence of filling fraction on the relative width of the minimum band gap is discussed.     

可见光波段SiO2/CdSe一维光子晶体及缺陷模的研究究

采用SiO2/CdSe构建了可见光波段一维光子晶体结构,并在其中引入LiTaO3缺陷层。利用传输矩阵法,分析了电磁波在无缺陷与含LiTaO3缺陷层两种光子晶体中的带隙结构,系统地研究了缺陷层参数对光子晶体可见光波段带隙结构的影响规律。计算结果表明：LiTaO3的引入,有利于带隙宽度的增加,调整缺陷层结构参数,缺陷模的位置可在不同颜色区域出现,如红光、黄光等缺陷模。该结构有望用于制作可见光波段的滤波器。     

Defect calculations with quasiparticle correction: A revisited study of iodine defects in CH3NH3PbI3

Defect levels in semiconductor band gaps play a crucial role in functionalized semiconductors for practical applications in optoelectronics;however,first-principle defect calculations based on exchange-correlation functionals,such as local density approximation,grand gradient approximation(GGA),and hybrid functionals,either underestimate band gaps or misplace defect levels.In this study,we revisited iodine defects in CH₃NH₃PbI₃ by combining the accuracy of total energy calculations of GGA and single-electron level calculation of the GW method.The combined approach predicted neutral Im_i to be unstable and the transition level of Im_i(+1/-1)to be close to the valence band maximum.Therefore,Im_i may not be as detrimental as previously reported.Moreover,Vm I may be unstable in the-1 charged state but could still be detrimental owing to the deep transition level of Vm I(+1/0).These results could facilitate the further understanding of the intrinsic point defect and defect passivation observed in CH₃NH₃PbI₃.