Wu Xiao-Bin, Wang Jia, Wang Rui, Xu Ji-Ying, Tian Qian, Yu Jian-Yuan
State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments, Tsinghua University, Beijing 100084, China.
Guang Pu Xue Yu Guang Pu Fen Xi. 2009 Oct;29(10):2681-5.
Raman spectroscopy is a powerful technique in the characterization of carbon nanotubes (CNTs). However, this spectral method is subject to two obstacles. One is spatial resolution, namely the diffraction limits of light, and the other is its inherent small Raman cross section and weak signal. To resolve these problems, a new approach has been developed, denoted tip-enhanced Raman spectroscopy (TERS). TERS has been demonstrated to be a powerful spectroscopic and microscopic technique to characterize nanomaterial or nanostructures. Excited by a focused laser beam, an enhanced electric field is generated in the vicinity of a metallic tip because of the surface plasmon polariton (SPP) and lightening rod effect. Consequently, Raman signal from the sample area illuminated by the enhanced field nearby the tip is enhanced. At the same time, the topography is obtained in the nanometer scale. The exact corresponding relationship between the localized Raman and the topography makes the Raman identification at the nanometer scale to be feasible. In the present paper, based on an inverted microscope and a metallic AFM tip, a tip-enhanced Raman system was set up. The radius of the Au-coated metallic tip is about 30 nm. The 532 nm laser passes through a high numerical objective (NA0.95) from the bottom to illuminate the tip to excite the enhanced electric field. Corresponding with the AFM image, the tip-enhanced near-field Raman of a 100 nm diameter single-walled carbon nanotube (SWNT) bundles was obtained. The SWNTs were prepared by arc method. Furthermore, the near-field Raman of about 3 SWNTs of the bundles was received with the spatial resolution beyond the diffraction limit. Compared with the far-field Raman, the enhancement factor of the tip-enhanced Raman is more than 230. With the super-diffraction spatial resolution and the tip-enhanced Raman ability, tip-enhanced Raman spectroscopy will play an important role in the nano-material and nano-structure characterization.
拉曼光谱是表征碳纳米管（CNT）的一种强大技术。然而，这种光谱方法存在两个障碍。一个是空间分辨率，即光的衍射极限，另一个是其固有的小拉曼截面和微弱信号。为了解决这些问题，已开发出一种新方法，称为尖端增强拉曼光谱（TERS）。TERS已被证明是一种用于表征纳米材料或纳米结构的强大光谱和显微技术。由于表面等离子体激元极化子（SPP）和避雷针效应，聚焦激光束激发时，金属尖端附近会产生增强电场。因此，来自尖端附近增强场照射的样品区域的拉曼信号得到增强。同时，可在纳米尺度上获得形貌。局部拉曼与形貌之间的确切对应关系使得纳米尺度的拉曼识别成为可能。在本文中，基于倒置显微镜和金属原子力显微镜（AFM）尖端，建立了一个尖端增强拉曼系统。涂金金属尖端的半径约为30纳米。532纳米激光从底部穿过高数值孔径物镜（NA0.95）以照射尖端，激发增强电场。与AFM图像对应，获得了直径为100纳米的单壁碳纳米管（SWNT）束的尖端增强近场拉曼光谱。这些SWNT是通过电弧法制备的。此外，接收了该束中约3根SWNT的近场拉曼光谱，其空间分辨率超过了衍射极限。与远场拉曼相比，尖端增强拉曼的增强因子超过230。凭借超衍射空间分辨率和尖端增强拉曼能力，尖端增强拉曼光谱将在纳米材料和纳米结构表征中发挥重要作用。
