Finite-difference time-domain studies of the optical properties of nanoshell dimers
Finite-difference time-domain studies of the optical properties of nanoshell dimers
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DOI：
10.1021/jp044382x
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发表时间：
2005-05-26
影响因子：
3.3
通讯作者：
Nordlander, P
中科院分区：
文献类型：
--
作者：
Oubre, C;Nordlander, P
采用时域有限差分法（FDTD）研究了金属纳米壳二聚体的光学性质。我们讨论的问题，具体的二聚体系统的数值收敛。我们目前的结果为同源二聚体和异源二聚体。结果表明，延迟效应必须考虑到一个准确的描述现实尺寸的纳米粒子二聚体。纳米壳二聚体的光学性质被发现是强烈的偏振依赖。当入射脉冲的电场平行于二聚体轴排列时，二聚体中纳米壳之间发生最大耦合。在消光截面的二聚体中的峰的波长示出为变化超过100 nm，这取决于入射电场极化。计算表明，电场增强的二聚体结强烈依赖于二聚体分离。最大场增强发生在二聚体结中，并且以在空间的其他区域中降低的电场增强为代价。我们调查的有用性的nanoshell二聚体衬底的Sers通过集成的四次方的电场增强的纳米粒子的表面周围的二聚体分离和波长的函数。Sers效率强烈依赖于二聚体的分离，但在一个特定的点比最大电场增强的四次方弱得多。Sers效率也被发现强烈依赖于入射光的波长。最大的Sers效率发生共振激发的二聚体等离子体。
The optical properties of metallic nanoshell dimers are investigated using the finite difference time domain (FDTD) method. We discuss issues of numerical convergence specific for the dimer system. We present results for both homodimers and heterodimers. The results show that retardation effects must be taken into account for an accurate description of realistic size nanoparticle dimers. The optical properties of the nanoshell dimer are found to be strongly polarization dependent. Maximal coupling between the nanoshells in a dimer occurs when the electric field of the incident pulse is aligned parallel to the dimer axis. The wavelengths of the peaks in the extinction cross section of the dimer are shown to vary by more than 100 nm, depending on the incident electric field polarization. The calculations show that electric field enhancements in the dimer junctions depend strongly on dimer separation. The maximum field enhancements occur in the dimer junction and at the expense of a reduced electric field enhancement in other regions of space. We investigate the usefulness of nanoshell dimers substrates for SERS by integrating the fourth power of the electric field enhancements around the surfaces of the nanoparticles as a function of dimer separation and wavelength. The SERS efficiency is shown to depend strongly on dimer separation but much weaker than the fourth power of the maximum electric field enhancement at a particular point. The SERS efficiency is also found to depend strongly on the wavelength of the incident light. Maximum SERS efficiency occurs for resonant excitation of the dimer plasmons.