Yi K J, He X N, Zhou Y S, Xiong W, Lu Y F
Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0511, USA.
Rev Sci Instrum. 2008 Jul;79(7):073706. doi: 10.1063/1.2956977.
Conventional Raman spectroscopy (RS) suffers from low spatial resolution and low detection sensitivity due to the optical diffraction limit and small interaction cross sections. It has been reported that a highly localized and significantly enhanced electromagnetic field could be generated in the proximity of a metallic tip illuminated by a laser beam. In this study, a tip-enhanced RS system was developed to both improve the resolution and enhance the detection sensitivity using the tip-enhanced near-field effects. This instrument, by combining RS with a scanning tunneling microscope and side-illumination optics, demonstrated significant enhancement on both optical sensitivity and spatial resolution using either silver (Ag)-coated tungsten (W) tips or gold (Au) tips. The sensitivity improvement was verified by observing the enhancement effects on silicon (Si) substrates. Lateral resolution was verified to be below 100 nm by mapping Ag nanostructures. By deploying the depolarization technique, an apparent enhancement of 175% on Si substrates was achieved. Furthermore, the developed instrument features fast and reliable optical alignment, versatile sample adaptability, and effective suppression of far-field signals.
传统拉曼光谱(RS)由于光学衍射极限和小的相互作用截面而存在空间分辨率低和检测灵敏度低的问题。据报道,在激光束照射的金属尖端附近可以产生高度局域化且显著增强的电磁场。在本研究中,开发了一种尖端增强拉曼光谱系统,利用尖端增强近场效应来提高分辨率并增强检测灵敏度。该仪器通过将拉曼光谱与扫描隧道显微镜和侧面照明光学系统相结合,使用涂银(Ag)的钨(W)尖端或金(Au)尖端在光学灵敏度和空间分辨率方面都有显著提高。通过观察对硅(Si)衬底的增强效应验证了灵敏度的提高。通过绘制银纳米结构,横向分辨率被验证低于100 nm。通过采用去极化技术,在硅衬底上实现了175%的明显增强。此外,所开发的仪器具有快速可靠的光学对准、通用的样品适应性以及有效抑制远场信号的特点。
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