Novel routes to electromagnetic enhancement and its characterisation in surface- and tip-enhanced Raman scattering.
Novel routes to electromagnetic enhancement and its characterisation in surface- and tip-enhanced Raman scattering.
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DOI：
10.1039/c7fd00128b
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发表时间：
2017-11
影响因子：
3.4
通讯作者：
P. Dawson;D. Frey;Vijith Kalathingal;R. Mehfuz;J. Mitra
中科院分区：
文献类型：
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作者：
P. Dawson;D. Frey;Vijith Kalathingal;R. Mehfuz;J. Mitra
由于所使用的复杂衬底结构，在增强型拉曼光谱中对电磁分量的定量理解通常难以实现。因此，我们转向两个结构简单的系统，适合详细的建模。第一个是尖端增强拉曼散射下的电子扫描隧道显微镜控制（STM-TERS），呼吁理解从STM的光子发射的背景下开发的，有人认为，本地化的表面等离子体模式驱动的拉曼增强存在于可见光和近红外区仅凭借显着修改的尖端和样品金属（金在这里）的光学性质。这是由于强直流场诱导（109 V m-1）的非线性校正的介电函数的金通过三阶极化率项。此外，在建模中显示了低于5 nm的空间分辨率。其次，我们提出了一种新的部署混合等离子体波导模式的表面增强拉曼散射（HPWG-SERS）。这在纳米级宽度的高折射率电介质材料（这里考虑GaAs纳米棒和100 nm Si板）和金属之间的约10 nm氧化物“间隙”中提供了电磁能量的强约束，产生了作为波长的函数的拉曼增强因子的单调变化，没有长波长截止，这两个特征与STM-TERS形成对比。
Quantitative understanding of the electromagnetic component in enhanced Raman spectroscopy is often difficult to achieve on account of the complex substrate structures utilised. We therefore turn to two structurally simple systems amenable to detailed modelling. The first is tip-enhanced Raman scattering under electron scanning tunnelling microscopy control (STM-TERS) where, appealing to understanding developed in the context of photon emission from STM, it is argued that the localised surface plasmon modes driving the Raman enhancement exist in the visible and near-infrared regime only by virtue of significant modification to the optical properties of the tip and sample metals (gold here). This is due to the strong dc field-induced (∼109 V m-1) non-linear corrections to the dielectric function of gold via the third order susceptibility term in the polarisation. Also, sub-5 nm spatial resolution is shown in the modelling. Secondly, we suggest a novel deployment of hybrid plasmonic waveguide modes in surface enhanced Raman scattering (HPWG-SERS). This delivers strong confinement of electromagnetic energy in a ∼10 nm oxide 'gap' between a high-index dielectric material of nanoscale width (a GaAs nanorod and a 100 nm Si slab are considered here) and a metal, yielding a monotonic variation in the Raman enhancement factor as a function of wavelength with no long-wavelength cut-off, both features that contrast with STM-TERS.