Quantitative analysis of polarization-controlled tip-enhanced Raman imaging through the evaluation of the tip dipole.
Quantitative analysis of polarization-controlled tip-enhanced Raman imaging through the evaluation of the tip dipole.
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DOI：
10.1021/nn5031803
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发表时间：
2014-09
期刊：
影响因子：
17.1
通讯作者：
Toshihiro Mino;Y. Saito;P. Verma
中科院分区：
文献类型：
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作者：
Toshihiro Mino;Y. Saito;P. Verma
尖端增强拉曼光谱（TERS）中的偏振分析具有巨大的优势，因为它允许人们在纳米尺度下研究样品的高度定向的本征性质。然而，无论是评估还是控制TERS中的近场光的偏振特性都不像通常的远场照明那样简单，因为随机的金属纳米结构附着在尖端顶点上。在这项研究中，我们已经开发了一种方法，成功地分析了近场光的偏振TERS从金属尖端的诱导偶极子产生的散射图案。在偶极子近似下，我们测量了偶极子在远离焦平面的平面上的图像，其中关于偶极子振荡方向的信息是完整的。由离焦斑图确定偶极子振荡方向，通过绿色函数计算近场光强度分布，从偶极子振荡方向判断近场光偏振。在评估了一些制造的尖端的极化后，我们使用这些尖端测量单壁碳纳米管的TERS图像，并确认TERS图像的对比度取决于偶极子的振荡方向，这也被发现与计算的TERS图像非常吻合，验证了我们的技术定量估计的近场的极化。我们的技术将导致更好的定量分析TERS成像与偏振影响的考虑，给纳米材料的行为更好的理解。
Polarization analysis in tip-enhanced Raman spectroscopy (TERS) is of tremendous advantage, as it allows one to study highly directional intrinsic properties of a sample at the nanoscale. However, neither evaluation nor control of the polarization properties of near-field light in TERS is as straightforward as in usual far-field illumination, because of the random metallic nanostructure attached to the tip apex. In this study, we have developed a method to successfully analyze the polarization of near-field light in TERS from the scattering pattern produced by the induced dipole in the metallic tip. Under dipole approximation, we measured the image of the dipole at a plane away from the focal plane, where the information about the direction of the dipole oscillation was intact. The direction of the dipole oscillation was determined from the defocused pattern, and then the polarization of near-field light was evaluated from the oscillation direction by calculating the intensity distribution of near-field light through Green's function. After evaluating the polarization of some fabricated tips, we used those tips to measure TERS images from single-walled carbon nanotubes and confirmed that the contrast of the TERS image depended on the oscillation direction of the dipole, which were also found in excellent agreement with the calculated TERS images, verifying that the polarization of the near-field was quantitatively estimated by our technique. Our technique would lead to better quantitative analysis in TERS imaging with consideration of polarization impact, giving a better understanding of the behavior of nanomaterials.