Plasmonic Resonances of Closely Coupled Gold Nanosphere Chains
Plasmonic Resonances of Closely Coupled Gold Nanosphere Chains
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DOI：
10.1021/jp8083869
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发表时间：
2009-02-19
影响因子：
3.7
通讯作者：
Ford, Michael J.
中科院分区：
文献类型：
--
作者：
Harris, Nadine;Arnold, Matthew D.;Ford, Michael J.
在粒子近场强耦合的情况下，利用T矩阵方法计算了有序金纳米球阵列的光学性质。该阵列由直径为15 nm的球的一维链组成，其中链中的球的数量和颗粒间的间距是变化的。已进行计算链长达150个粒子的长度和0.5和30 nm之间的粒子间的间距。入射光偏振沿着链的轴（纵向）和垂直（横向），它被认为是，在后一种情况下，沿着和垂直于链轴的波矢量。对于固定的链长的纵向等离子体共振红移，相对于一个孤立的球的共振，作为粒子间的间距减少。在等离子体共振的移位似乎不遵循指数依赖于这些扩展的颗粒阵列的间隙大小。峰值位移与距离成反比，这一结果与短距离下两个球体之间的货车德瓦尔斯吸引力一致，其也随1/d变化。横向等离子体共振在相反的方向上移动的粒子间的间隙减少，这个位移是相当小的，接近500 nm的差距趋于零。对于固定的间隙，增加链中的粒子数量对纵向和横向等离子体激元具有类似的影响。然而，在这种情况下，随着链长的增加，纵向等离子体趋于渐近值，渐近值由粒子间的间距决定。在这里，渐近线的方法是指数的，特征长度约为两个粒子，在小的粒子间距。这种方法的渐近线的链长变得无限已被验证在有限元计算与周期性的边界条件。
The optical properties of an ordered array of gold nanospheres have been calculated using the T-matrix method in the regime where the near-fields of the particles are strongly coupled. The array consists of a one-dimensional chain of spheres of 15 nm diameter where the number of spheres in the chain and interparticle spacing is varied. Calculations have been performed with chains up to 150 particles in length and with an interparticle spacing between 0.5 and 30 nm. Incident light polarized along the axis of the chain (longitudinal) and perpendicular (transverse) to it are considered, and in the latter case for wavevectors along and perpendicular to the chain axis. For fixed chain length the longitudinal plasmon resonance red shifts, relative to the resonance of an isolated sphere, as the interparticle spacing is reduced. The shift in the plasmon resonance does not appear to follow an exponential dependence upon gap size for these extended arrays of particles. The peak shift is inversely proportional to the distance, a result that is consistent with the van der Waals attraction between two spheres at short range, which also varies as 1/d. The transverse plasmon resonance shifts in the opposite direction as the interparticle gap is reduced; this shift is considerably smaller and approaches 500 nm as the gap tends to zero. Increasing the number of particles in the chain for a fixed gap has a similar effect on the longitudinal and transverse plasmon. In this case, however, the longitudinal plasmon tends toward an asymptotic value with increasing chain length, with the asymptotic value determined by the interparticle spacing. Here, the approach to the asymptote is exponential with a characteristic length of approximately two particles, at small interparticle spacings. This approach to an asymptote as the chain length becomes infinite has been verified in a finite element calculation with periodic boundary conditions.