Nanosphere lithography: Effect of the external dielectric medium on the surface plasmon resonance spectrum of a periodic array of sliver nanoparticles
Nanosphere lithography: Effect of the external dielectric medium on the surface plasmon resonance spectrum of a periodic array of sliver nanoparticles
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DOI：
10.1021/jp9926802
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发表时间：
1999-11-11
影响因子：
3.3
通讯作者：
Van Duyne, RP
中科院分区：
文献类型：
--
作者：
Jensen, TR;Duval, ML;Van Duyne, RP
本文研究了溶剂对纳米球光刻法制备的表面受限银纳米粒子周期性杂散光消谱的影响。利用NSL，可以系统地改变纳米颗粒的面外高度，通过热退火，可以控制纳米颗粒的形状。我们研究了四种不同的纳米颗粒阵列样品：三种样品的纳米颗粒形状为截尾四面体，但面外高度不同，一种样品的纳米颗粒形状为扁椭球体。通过在12 μ m空间分辨率下进行紫外-可见消光光谱测量，我们表明，作为NSL制造过程的副产品出现的缺陷位点在宏观尺度消光光谱中起着可以忽略不计的作用。研究发现，扁椭球形纳米粒子的消光光谱对周围介质最不敏感，而面外高度最小的截形四面体纳米粒子的消光光谱最敏感。消光最大值的1 nm位移对应于外部介质折射率的0.005变化。给出了基于离散偶极子近似（DDA）的理论计算。DDA是一种耦合有限元方法，能够计算任意形状和大小的粒子的光消光。实验结果与理论结果的差异对于扁圆椭球体粒子来说很小，而对于截尾四面体粒子来说，随着它们变得更扁圆，实验结果与理论结果的差异逐渐增大。DDA理论预测，随着溶剂折射率的增加，消光最大值的红移比实验观察到的要大得多。
In this paper we examine the effect of solvent on the optical extinction spectrum of periodic strays of surface-confined silver nanoparticles fabricated by nanosphere lithography (NSL). BS use of NSL, it is possible to systematically vary the out-of-plane height of the nanoparticles and by thermal annealing, we can control the nanoparticle shape. We have studied four separate samples of nanoparticle arrays: three samples have nanoparticles that are truncated tetrahedral in shape but that differ in out-of-plane height and one sample has nanoparticles that are oblate ellipsoidal in shape. By performing UV-vis extinction spectroscopy measurements at 12 mu m spatial resolution, we show that the defect sites that occur as a byproduct of the NSL fabrication process play a negligible role in the macroscale extinction spectrum. We find that the extinction spectrum of the nanoparticles that are oblate ellipsoidal in shape is least sensitive to the surrounding dielectric medium, and the extinction spectrum of the nanoparticles that are truncated tetrahedral in shape with the smallest out-of-plane height is most sensitive. A 1 nm shift in the extinction maximum corresponds to a 0.005 change in the refractive index of the external medium. Theoretical calculations based on the discrete dipole approximation (DDA) are presented. The DDA is a coupled finite element method capable of calculating the extinction of light for particles of arbitrary shape and size. The discrepancy between the experimental and theoretical results is small for the oblate ellipsoidal-shaped particle but progressively increases for the truncated tetrahedral-shaped particles as they become more oblate. This discrepancy is lessened by including the effect of substrate-particle interactions in the calculation, The DDA theory predicts a significantly larger red shift in the extinction maximum with increasing solvent refractive index than is observed experimentally.