Infrared, Raman and Visible Reflectance Spectroscopic Imaging

得到的结果说明了尖端增强拉曼光谱(TERS)和成像在一种新的顶部照明几何结构中的应用。径向偏振光束被用来产生沿光束传播方向、垂直于表面的电场分量，与线偏振光束相比，获得了五倍的增强。这种倍增增强有助于区分近场信号和远场拉曼背景。顶部照明配置允许应用TERS来研究各种表面的分子，例如金、玻璃和硅。研究了包括单壁碳纳米管在内的多种材料的近场拉曼光谱。获得了足够的增强，以允许获得不同直径的大束碳纳米管的表面分布的亚衍射分辨率的高光谱拉曼成像立方体。为了进一步促进复杂生物样品的纳米粒子增强拉曼成像，利用背散射显微镜的配置，探索了使用径向和方位偏振聚焦在金纳米粒子AFM尖端的更高阶模的使用。特别是，径向偏振配置提供了增强的空间分辨率。这是金属纳米粒子中感应电子振荡方向的结果，该方向由激光焦点处的电磁场定向。具体地说，电磁增强的方向性是至关重要的，这样被观察的分子在纳米结构尖端的顶端经历了最大的增强场。这些结果表明，TERS有可能在纳米尺度上提供分子分布的洞察力，例如，那些代表疾病状态的系统。

Results were obtained which illustrated the use of tip-enhance Raman spectroscopy (TERS) and imaging in a novel top illumination geometry. A radially polarized beam was used to generate an electric field component in the direction of beam propagation, normal to the surface, resulting in a five times enhancement compared to a linearly polarized beam. This multiplicative enhancement facilitates a discrimination of the near-field signal from the far-field Raman background. The top illumination configuration allows the application of TERS for investigating molecules on a variety of surfaces, such as gold, glass and silicon. The near field Raman spectra of a variety of materials, including single wall carbon nanotubes, were examined. Sufficient enhancement was obtained to permit the obtaining of a sub-diffraction resolution hyperspectral Raman imaging cube of the surface distribution of large bundles of carbon nanotubes of varying diameter. To further facilitate nanoparticle enhanced Raman imaging of complex biological specimens, the use of higher laser order modes with radial and azimuthal polarizations focused onto a gold nanoparticle AFM tip was explored using a back-scattering microscope configuration. In particular, the radial polarized configuration provided enhanced spatial resolution. This is a consequence of the direction of the induced electron oscillation in the metal nanoparticle, which is oriented by the electromagnetic field at the laser focus. Specifically, the directionality of the electromagnetic enhancement is critical such that the molecule under observation experiences the greatest enhanced field at the apex of the nanostructure tip. These results indicate the potential for TERS to provide insights in molecular distributions on the nanoscale, as, for example, those systems representative of diseased states.