Jiang Yang, Wang An, Ren Bin, Tian Zhong-Qun
State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.
Langmuir. 2008 Oct 21;24(20):12054-61. doi: 10.1021/la801376p. Epub 2008 Sep 6.
The near-field surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) images of tris(bipyridine)ruthenium(II) adsorbed on a silver nanoparticles-coated substrate were obtained with a scanning near-field optical microscope (SNOM, or near-field scanning optical microscopy, NSOM) using a cantilever tip. In comparison with the most widely used fiber tip for SNOM, the cantilever tip has higher optical throughput and better thermal stability, making it more suitable for detecting the extremely low Raman signal in the near-field spectroscopic investigations. Our preliminary results show that the near-field SERS with the higher spatial resolution can provide richer fingerprint information than the far-field SERS. A comparison of the two types of images shows that there are more SERS than SEF hot spots, and the two types of hot spots do not overlap. More surprisingly, the near-field SERS spectra differ from the far-field SERS spectra obtained on the same sample in the band frequency and relative intensities of some major Raman bands, and some IR-active bands were observed with the near-field mode. These results are explained mainly by the electric field gradient effect and heterogeneous polarization character that operate only in the near-field SERS.
利用扫描近场光学显微镜（SNOM，即近场扫描光学显微镜，NSOM）的悬臂探针，获得了吸附在银纳米颗粒包覆基底上的三联吡啶钌（II）的近场表面增强拉曼散射（SERS）和表面增强荧光（SEF）图像。与SNOM中使用最广泛的光纤探针相比，悬臂探针具有更高的光通量和更好的热稳定性，使其更适合在近场光谱研究中检测极低的拉曼信号。我们的初步结果表明，具有更高空间分辨率的近场SERS比远场SERS能提供更丰富的指纹信息。两种图像的比较表明，SERS热点比SEF热点更多，且两种热点不重叠。更令人惊讶的是，近场SERS光谱在某些主要拉曼带的谱带频率和相对强度上与在同一样品上获得的远场SERS光谱不同，并且在近场模式下观察到了一些红外活性带。这些结果主要由仅在近场SERS中起作用的电场梯度效应和非均匀极化特性来解释。
