On the significance of Shalaev's "hot spots' in ensemble and single-molecule SERS by adsorbates on metallic films at the percolation threshold
On the significance of Shalaev's "hot spots' in ensemble and single-molecule SERS by adsorbates on metallic films at the percolation threshold
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DOI：
10.1002/jrs.1524
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发表时间：
2006-09-01
影响因子：
2.5
通讯作者：
Otto, A.
中科院分区：
文献类型：
--
作者：
Otto, A.
最近的模型等离子体局域化和局部电磁（EM）场分布的银在玻璃上的薄膜在渗流阈值（Shalaev和合作者）已经成功地模拟了扫描近场光学显微镜（SNOM）的图片。清晰可见的所谓热点被认为对超过10（11）的热点处的吸附物的拉曼增强有很大贡献。然而，当适当地考虑光学互易性定理时，在渗滤阈值下，在银岛膜中有助于表面增强拉曼散射（Sers）的总体EM增强因子在这里计算为约3 X 10（5），比Shalaev和合作者测量的总体Sers增强低一个数量级。给定在发现嵌入在热点处涂覆银岛膜的LB膜内的单个染料分子的实验概率为0.003（Aroca和合作者的观察），并且假设这些热点是“Shalaev型”的，则相应的EM增强不超过10（6）至10（7）。此外，这与实验结果也是一致的。这种增强足以观察到单个染料分子的Sers。早期的经验法则产生的增强数字，即增强由局部场增强的四次方给出，是误导的几个数量级的斯托克位移超过约300 cm（-1）。版权所有（c）2006约翰威利父子有限公司。
Recent models of plasmon localization and local electromagnetic (EM) field distribution in silver-on-glass films at the percolation threshold (Shalaev and collaborators) have successfully modelled the scanning near-field optical microscopy (SNOM) pictures. The clearly visible so-called hot spots are believed to contribute heavily to the Raman enhancement for adsorbates at the hot spots exceeding 10(11). However, when the theorem of optical reciprocity is properly taken into account, the ensemble EM enhancement factor contributing to surface-enhanced Raman scattering (SERS) in silver island films at the percolation threshold is calculated here as about 3 X 10(5), an order of magnitude lower than the overall SERS enhancement measured by Shalaev and collaborators. Given the experimental probability of 0.003 in finding a single dye molecule that is embedded within a Langmuir-Blodgett (LB) film coating a silver island film at a hot spot (observations of Aroca and collaborators), and assuming that these hot spots are of 'Shalaev-type', the corresponding EM enhancement does not exceed 10(6) to 10(7). In addition, this is in good agreement with the experiment. This enhancement is sufficient to observe the SERS from single dye molecules.Earlier enhancement numbers produced by the rule of thumb, that the enhancement is given by the fourth power of the local field enhancement, are misleading by several orders of magnitude for Stoke shifts exceeding approximately 300 cm(-1). Copyright (c) 2006 John Wiley & Sons, Ltd.