Resonant Raman Scattering of Single Walled Carbon Nanotubes by the two-laser irradiation method

单壁碳纳米管(SWNTs)中电子能带之间的光学跃迁表现出强烈的共振行为，这是由于与一维纳米管结构相关的电子密度中的尖峰结构所致。由于共振能量依赖于单壁碳纳米管的手性，因此单色激光只能激发具有相应手性的单壁碳纳米管。可以观察到伴随着这种带间共振的共振拉曼散射，手性可以根据共振能量和声子能量的组合来粗略地确定。在本研究中，当一束激光激发具有特定手性的单壁碳纳米管中的电子态时，为了阐明第一次激光照射在单壁碳纳米管中诱导的过程，我们研究了另一种激光的共振喇曼散射。结果表明，在最显著的情况下，红外脉冲激光激发半导体单壁碳纳米管的第二电子能带，用能量相当于第三带跃迁的可见光激光激发半导体单壁碳纳米管的共振拉曼光谱。关于手性选择性还原过程，得到了一些新的结果，如阈值红外光谱、激光功率、还原速率和还原量等。虽然拉曼散射实验的精确度还有待提高，但双激光辐照方法在单壁碳纳米管的手性研究和手性选择方面仍具有广阔的应用前景。

Optical transitions between electronic bands in single-walled carbon nanotubes (SWNTs) shows intense resonant behavior due to spike-like structures in the electronic density of states relating to the one-dimensional nanotube structures. Since the resonance energies depend on the chiralities of SWNT, monochromatic laser light will excite only the SWNTs with the corresponding chirality. Resonant Raman scattering can be observed accompanying such band-to-band resonance, and the chirality can be roughly determined from the combination of the resonance energy and the phonon energy of a radial breathing mode in SWNT. In this study, while a laser light excites the electronic states in SWNTs with specific chirality, resonant Raman scattering is studied by another laser light in order to clarify the processes induced in the SWNTs by the first laser irradiation. As the results, in the most remarkable case, SWNTs are decreased by the infrared pulse laser which excites the second electronic bands in semiconducting SWNTs has been observed in the resonant Raman spectra by the visible laser that has the energy corresponding to the third-band transitions. Some new results about the chirality-selective reduction processes have been obtained, and for example, the threshold IR, laser power, reduction rates, and reduction amounts have been clarified. Although some improvements in the accuracy of the Raman scattering experiments are necessary, the two-laser irradiation method will be promising for the clarification and selection of the chiralities of SWNTs.