Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station A5300, Austin, Texas 78712, USA.
ACS Nano. 2011 Feb 22;5(2):1033-41. doi: 10.1021/nn102498h. Epub 2011 Jan 13.
We present a new approach for subdiffraction-limited far-field Raman spectroscopy of single carbon nanotubes using through-the-objective total internal reflection (TIR) excitation coupled to an atomic force microscope (AFM). By using this approach, we are able to detect spectroscopic signatures of structural changes along a single nanotube with nanometer resolution. A single multiwalled carbon nanotube is mounted on an AFM tip and imaged while tapping on the surface of a glass coverslip. As the angle of incidence of the excitation field is changed, we are able to tune the penetration depth of the evanescent field by steps as small as 2-10 nm. An increase in the ratio of the Raman D band (the disorder band) to G band (the in-plane graphitic band) of the carbon nanotube was demonstrated as the penetration depth decreased, indicating that most defects are concentrated at the end of the nanotube. We also observed frequency shifts of the G band as we changed the penetration depth. By changing the polarization of the incident beam, we are able detect the orientation and possible local curvature in the nanotubes. Coupling through-the-objective TIR with AFM is a powerful technique for studying structural and chemical properties of carbon nanotubes and can be easily extended to many other nanoscale/molecular systems.
我们提出了一种新的方法，用于使用通过物镜的全内反射（TIR）激发结合原子力显微镜（AFM）对单个碳纳米管进行亚衍射极限远场拉曼光谱学研究。通过使用这种方法，我们能够以纳米级分辨率检测沿单个纳米管的结构变化的光谱特征。将单个多壁碳纳米管安装在 AFM 尖端上，并在玻璃盖玻片表面上进行敲击成像。随着激发场的入射角的变化，我们能够以 2-10nm 的小步长调谐消逝场的穿透深度。随着穿透深度的减小，碳纳米管的 D 带（无序带）与 G 带（平面石墨带）的比率增加，表明大多数缺陷集中在纳米管的末端。当我们改变穿透深度时，我们还观察到 G 带的频移。通过改变入射光束的偏振，我们能够检测纳米管的取向和可能的局部曲率。通过物镜的 TIR 与 AFM 的耦合是研究碳纳米管的结构和化学性质的强大技术，并且可以很容易地扩展到许多其他纳米/分子系统。
