Effect of sample and substrate electric properties on the electric field enhancement at the apex of SPM nanotips
Effect of sample and substrate electric properties on the electric field enhancement at the apex of SPM nanotips
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DOI：
10.1021/jp0523120
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发表时间：
2005-08-25
影响因子：
3.3
通讯作者：
Elfick, A
中科院分区：
文献类型：
--
作者：
Notingher, I;Elfick, A
建立了有限元模型，确定了薄层样品尖端增强拉曼光谱的最佳实验条件。通过在有限元模型中包含具有薄介质样品的介质或金属衬底，并考虑金属材料的介电特性与波长的关系，来模拟实验条件。衬底/S衬底和SPM针尖之间的电磁耦合导致了依赖于衬底介电常数和激发波长的散射电场的空间分布和大小的显著变化。当激发波长为532 nm(近共振波长)时，金SPM针尖和金衬底的拉曼散射高达10(8)，空间分辨率接近8 nm。对于厚度类似于4 nm的介质样品，拉曼散射强度的增强估计类似于10(5)；对于介质样品，这并不显著地依赖于样品的介电常数。这些结果表明，对于每一个单独的应用，TERS实验条件应该被估计和优化，考虑到所涉及材料的几何因素和电学性质。这样的优化可以扩大TERS的应用范围，使其适用于本征拉曼散射较弱的样品，如生物样品。
Finite element (FE) models were built to define the optimal experimental conditions for tip-enhanced Raman spectroscopy (TERS) of thin samples. TERS experimental conditions were mimicked by including in the FE models dielectric or metallic substrates with thin dielectric samples and by considering the wavelength dependence of the dielectric properties for the metallic materials. Electromagnetic coupling between the sub strate/s ample and the SPM tips led to dramatic changes of both the spatial distribution and magnitude of the scattered electric field which depended on the substrate dielectric permittivity and excitation wavelength. Raman scattering as high as 10(8) with a spatial resolution of similar to 8 nm was estimated for gold SPM tips and gold substrate when excitation is performed at 532 nm (near-resonance wavelength). For dielectric samples (similar to 4 nm thick), the enhancement of Raman scattering intensity is estimated at similar to 10(5); this does not depend significantly on the sample dielectric permittivity for dielectric samples. These results suggest that TERS experimental conditions should be estimated and optimized for every individual application considering the geometric factors and electric properties of the materials involved. Such optimizations could enlarge the range of applications for TERS to samples eliciting weaker intrinsic Raman scattering, such as biological samples.