Simulation of Optical Devices Using Parallel FDTD Method

On this paper, we investigate the algorithm and efficiency of simulation of optical devices using parallel computing method, implement some real wavelength division multiplexing (WDM) components such as resonators to test the method's possibility and efficiency.     

Self consistent multi-fluid FDTD simulations of a nanosecond high power microwave discharge in air

FDTD simulations of the Maxwell equations are combined with the multi-fluid plasma equations to study the dynamics of a high power microwave discharge in air. The breakdown takes place in a short time of a few nanoseconds and the concentrations of electrons, ions, excited species, and the dissociation products are quickly enhanced. The breakdown time decreases with decreasing of the pressure and the pulse amplitude, while increases with increasing of the pulse width. N${{}_2}^{+}$ and O${}_2^{+}$ are the most important positive ions, whereas O^? is the most populated negative ion. For a single microwave pulse, the electron number density is large up to 1 μs, and the dissociation and excitation continue to increase the small radicals and excited species. Then the electron number density drops and the population of excited species declines. The ozone production becomes important after 1 μs when the three body association of O and O₂ dominates over the dissociation processes. The ozone number density continues to grow up to 5 ms, and then saturates at a value of 10²² m^?3. Quenching of electronically excited nitrogen molecules by O₂ molecules and the subsequent dissociation to atomic oxygen and generation of NO, are found to be important and can play a significant role in the ultrafast gas heating.     

金纳米棒的飞秒激光组装研究

金属纳米粒子对于研究表面等离子体共振具有非常重要的意义,其自组装形成的功能组装体能够展现出更加优异的整体协同性能.本文通过飞秒激光加工对金纳米棒直接进行组装,不引入其它的修饰剂,过程简单、快速(约1 min),不仅保留了金纳米棒表面等离子特性,且可以实现金纳米棒的任意精细图案化.将组装的微纳结构用于微流控芯片表面增强拉曼散射探测,可以得到很好的增强效果,为等离子体器件的制备提供了新的方法.     

表面等离激元探针的高介电灵敏度与液体折射率测定

利用金纳米棒在光照射下激发表面等离激元的性质,实验研究了其在不同介电环境下的吸收光谱.通过分析纵向等离子体共振吸收峰峰位随介质折射率的变化,获得了金纳米棒表面等离激元探针测量介质折射率的经验公式为n=(385.59)-1(λ/nm-290.56).利用金纳米棒表面等离激元探针的高介电灵敏度,测试了一些未知液体的折射率,并与阿贝折射仪测量法的结果相比较.结果与分析表明,本方法较之阿贝折射仪测量介质折射率的方法具有更高的精密度.因此,表面等离探针可用于拓展大学物理实验中的介质折射率测量实验.     

金纳米棒核／二氧化硅壳纳米复合结构的可控制备及细胞成像

采用模板合成以及溶胶凝胶方法制备了金纳米棒核／二氧化硅壳（GNR@SiO2）纳米复合粒子,探讨了这种新型纳米复合结构的可控制备、光谱性质、细胞毒性和细胞成像。通过紫外可见分光光度计、透射电镜、共聚焦显微镜对样品进行表征,结果表明：通过对反应时间的调控,获得的纳米复合粒子的二氧化硅壳层厚度可以控制在20～30nm。由于二氧化硅壳层的存在,大大提高了金纳米棒的稳定性,同时降低了金纳米棒的细胞毒性;此外,由于二氧化硅壳层具有良好的化学修饰作用,因此可以将荧光探针分子标记在二氧化硅壳层表面,修饰后的纳米复合粒子可以通过细胞内吞作用进入细胞,从而实现细胞内的光学成像。因此,该纳米粒子复合材料在生物传感、细胞成像以及光热治疗等方面有着良好的应用前景。     

UV-activated gas sensing properties of ZnS nanorods functionalized with Pd

Pd-functionalized ZnS nanorods were prepared for use as gas sensors. Scanning electron microscopy revealed the diameters and lengths of the nanorods ranging from 30 to 80 nm and from 2 to 5 μm, respectively. The diameter of Pd nanoparticles ranged from 2 to 5 nm. Transmission electron microscopy revealed that ZnS nanorods and Pd nanoparticles were monocrystalline and amorphous, respectively. The responses of multiple networked ZnS nanorods sensors to 1–5 ppm NO₂ were increased substantially by a combination of Pd functionalization and UV irradiation. Pristine ZnS nanorod sensors at room temperature in the dark showed a response (∼100%) almost independent of NO₂ concentration in a NO₂ concentration range of 1–5 ppm. Pristine ZnS nanorod sensors showed enhanced responses of 214–603% to 1–5 ppm NO₂ at room temperature under UV illumination. Pd-functionalized ZnS nanorods sensors showed further enhanced responses of 355–1511% to 1–5 ppm NO₂ at room temperature under UV illumination. The NO₂ gas sensing mechanism of the Pd-functionalized ZnS nanorods sensors under UV illumination is discussed in depth.     

Generalization of the FDTD algorithm for simulations of hydrodynamic nonlinear Drude model

In this paper we present a numerical method for solving a three-dimensional cold-plasma system that describes electron gas dynamics driven by an external electromagnetic wave excitation. The nonlinear Drude dispersion model is derived from the cold-plasma fluid equations and is coupled to the Maxwell’s field equations. The Finite-Difference Time-Domain (FDTD) method is applied for solving the Maxwell’s equations in conjunction with the time-split semi-implicit numerical method for the nonlinear dispersion and a physics based treatment of the discontinuity of the electric field component normal to the dielectric-metal interface. The application of the proposed algorithm is illustrated by modeling light pulse propagation and second-harmonic generation (SHG) in metallic metamaterials (MMs), showing good agreement between computed and published experimental results.     

Magnetotransport properties in magnetic nanotubes studied using Monte Carlo simulations

The dependences of the magnetoelectric transport properties of nanotubes on the temperature, diameter and anisotropy were simulated using the Monte Carlo method, the Heisenberg model and the Drude formula. The simulations included the effects of an external magnetic field, magnetocrystalline anisotropy and nearest neighbor interactions. Two types of nanotubes with different unit cells (square and hexagonal) were implemented. The influence of the nanotube geometry was also analyzed. A smaller dependence of the resistivity on the nanotube diameter and magnetocrystalline anisotropy was observed for the square unit cell nanotubes compared to the results obtained for the hexagonal unit cell nanotubes. Furthermore, lower fluctuations in the resistivity were observed in the former. In contrast, an external magnetic field had a greater influence on the resistivity of the square unit cell nanotubes than for the hexagonal unit cell nanotubes.     

Optoelectronic characteristics of CuO nanorods

Optoelectronic characteristics of p-type CuO nanorods, synthesized by a simple hydrothermal method, were investigated at different atmospheres and oxygen pressures. The CuO nanorods have lower resistance in air than in a vacuum, unlike the n-type semiconductors. This is explained in terms of the surface accumulation conduction. Measurements at different oxygen pressures indicate that oxygen has an important effect on the optoelectronic properties of p-type nanomaterials.     

水热反应中籽晶层对ZnO纳米棒的影响

以Zn(NO3)2·6H2O/HMT为反应物,通过低温水热反应过程,在籽晶衬底上制备了ZnO纳米棒,分别用场发射扫描电子显微镜和X射线衍射仪对ZnO纳米棒形貌与晶体结构进行了表征,并研究了不同方法制备的ZnO籽晶层以及籽晶层厚度对ZnO纳米棒形貌及结晶质量的影响.结果表明磁控溅射籽晶衬底上生长的ZnO纳米棒结晶质量最好,而籽晶层的厚度对ZnO纳米棒的垂直取向性有一定的影响.     

基于非分裂FDTD的左手介质电磁特性的研究

为验证左手介质的电磁特性,采用非分裂时域有限差分方法对左手介质的Drude模型进行建模.这种方法不需要对电场和磁场进行分裂,也不需要对PML空间进行特殊处理,吸收边界PML和工作空间可以通过参数转换来完成,并且构造的PML层为有耗介质,进入PML层的透射波将迅速衰减.它是一种准确而有效的分析色散和各向异性介质的方法,通过此方法有效地验证了左手介质的负折射效应、汇聚效应、相位补偿效应,充分验证了左手介质及其反常特性的存在性和此方法分析左手介质的有效性. 关键词： 左手介质 非分裂 时域有限差分 Drude     

PSTM成像的FDTD数值模拟

尝试用时域有限差分法(FDTD)分析采用不同探针时光子扫描隧道显微镜(PSTM)成像的分辨率和效率。对四种探针,即不镀膜,带菱形金尖,镀金膜有孔径,镀金膜无孔径的探针,用二维p极化波,满足全反射条件,并用样品台上方平行于界面的隐失波作为等效入射波源,用探针距离尖顶一定高度截面的玻印亭矢量计算散射场强。数值模拟结果表明,带纳米尺度金尖的探针具有最好成像的分辨率和效率,镀膜无孔径和镀膜孔径探针次之,不镀膜探针最差。     

1维介质光栅近场及其衍射的FDTD分析

 应用FDTD方法计算了单色平面波斜入射时1维介质光栅的近场，进而求出介质光栅的衍射效率。借助于周期边界条件，整个计算区域为周期结构的一个单元。考虑入射波在两种介质界面上会产生反射和透射，故在总场边界上引入入射波、反射波和透射波。给出了光栅单元截面为矩形和梯形的算例。该方法可用于斜入射情形下具有复杂结构和任意单元截面的介质栅近场及其衍射特性分析。     

Analysis of nonlinear PCF for birefringence application using FDTD method

The effect of ellipticity on birefringence in a hexagonal photonic crystal fiber having elliptical air holes with Kerr nonlinearity is investigated, with and without defect using finite difference time domain (FDTD) simulations. It is found that the birefringence increases with the increase of ellipticity. Further this analysis is extended to a double defect structure, where two adjacent air holes are omitted horizontally from the hexagonal structure. This double defect structure is found to have more birefringence than the structure without defect. It is raveled that birefringence due to no defect is more for lower value of ellipticity; however at higher value of ellipticity, birefringence due to double defect is more than the one that could be due to no defect.     

Biopolymer-assisted self-assembly of ZnO nanoarchitectures from nanorods

We have investigated three-dimensional (3-D) architectures–microspheres and radial structures–based on biopolymer-assisted self-assembly from one-dimensional ZnO nanorods. The developed method is simple, rapid and cost-effective and can be used for self-assembly of different complex superstructures. A possible model of 3-D architectures self-assembled with biopolymer assistance is presented using minimum energy considerations. Scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy, micro–Raman spectroscopy and cathode luminescence investigations show that the novel 3-D architectures are built from high-purity ZnO nanorods with a wurtzite structure. The resulting radial structures show an intense ultraviolet (UV) cathode luminescence emission suggesting applications as UV light emitting diodes or lasers. Their structural characteristics endow them with a broad area of applications and offer a possibility to be used as fundamental low-dimensional building units. These building units open opportunities for the self-assembly of multifunctional nanostructured systems with applications in bioscience and nanomedicine, electronics and photonics.     

金纳米环结构的光学性质研究

采用离散偶极子近似方法(DDA)研究了两种不同形状的金纳米环结构的消光光谱及其近电场分布, 研究了等离子体消光峰的红移、蓝移现象及消光系数与结构参数之间的关系, 并与盘状的金纳米结构进行了比较. 在等离子体共振峰波长入射时, 金纳米环结构比金纳米盘结构产生更大的局域增强电场分布, 横截面为圆形的金纳米环结构比横截面为矩形的结构具有更大的局域增强电场分布, 更适合作为表面增强拉曼散射的衬底. 关键词： 离散偶极子近似 金纳米环 金纳米盘 光学性质     

Preparation of monodisperse bimetallic nanorods with gold nanorod core and silver shell and their plasmonic property and SERS efficiency

In this study, monodisperse bimetallic nanorods with gold (Au) nanorod core and silver (Ag) shell (Au@AgNRs) were synthesized through seed‐mediated growth process by reduction of AgNO₃ using Au nanorods with narrow size and shape distribution as seeds. With increasing the used amount of AgNO₃, the Ag shell thickness of their lateral facets is raised faster than that of their two tips, leading to a decrease of their aspect ratios. Four plasmon bands are observable on the extinction spectra of Au@AgNRs, which are attributed to the longitudinal dipolar plasmon mode, transverse dipolar plasmon mode, and octupolar plasmon mode of the core‐shell structured bimetallic nanorods, respectively. As their Ag shell thickness increases, their longitudinal plasmon band blue‐shifts notably with the transverse plasmon band blue‐shifting and the two octupolar plasmon bands red‐shifting slightly, due to the decrease of their aspect ratios and enhancement of Ag plasmon resonance contribution. When used as surface‐enhanced Raman scattering (SERS) substrate for probing minute amounts of 4‐mercaptobenzoic acid in aqueous solution, Au@AgNRs have much stronger SERS activity than Au nanorods, and the obtained Raman signals are highly reproducible arising from their excellent monodispersity. Their SERS activity is remarkably increased with their Ag shell thickness thanks to the enhancing surface electric field and the chemical enhancement associated with electronic ligand effect. Copyright © 2014 John Wiley & Sons, Ltd.     

Doping dependent room-temperature ferromagnetism and structural properties of dilute magnetic semiconductor ZnO:Cu nanorods

Copper doped ZnO nanoparticles were synthesized by the chemical technique based on the hydrothermal method. The crystallite structure, morphology and size were determined by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) for different doping percentages of Cu²⁺ (1-10%). TEM/SEM images showed formation of uniform nanorods, the aspect ratio of which varied with doping percentage of Cu²⁺. The wurtzite structure of ZnO gradually degrades with the increasing Cu²⁺ doping concentration and an additional CuO associated diffraction peak was observed above 8% of Cu²⁺ doping. The change in magnetic behavior of the nanoparticles of ZnO with varying Cu²⁺ doping concentrations was investigated using a vibrating sample magnetometer (VSM). Initially these nanoparticles showed strong room-temperature ferromagnetic behavior, however at higher doping percentage of copper the ferromagnetic behavior was suppressed and paramagnetic nature was enhanced.     

Optical properties of ZnO nanorods realised by aqueous chemical growth

Photoluminescence investigations of ZnO nanorods realised by an advanced two-step aqueous chemical growth process have been carried out revealing well-resolved near-band-edge emission accompanied by phonon replicas. The optical properties of nanorods with different lengths and diameters are quite similar indicating a good control of the growth process without influencing the optical properties even on plastic substrate. The near-band-edge emission has a very broad line-width of 10 meV. Annealing in Ar atmosphere reduces the deep-level emission with a corresponding increase of the near-band-edge emission.     

Three-Dimensional FDTD Analysis of Chiral Discontinuities in the Waveguide

A simple finite difference time domain (FDTD) scheme for chiral media is developed for modeling the chiral discontinuities in the waveguide with the aid of the second-order backward finite difference. The accuracy of the FDTD scheme is demonstrated by the comparison between our calculated results and those in the literature for achiral and chiral media. Comparisons of characteristics between chiral and achiral discontinuities in the waveguide are presented at last.