In situ Resonant Raman Spectroscopy in Carbon Nanotube Synthesis by Pulsed Laser Ablation Method

为了在脉冲激光烧蚀（PLA）法制备碳纳米管（CNT）过程中对CNT的性质进行真实的实时研究，设计并搭建了一套紧凑的拉曼光谱系统，该系统由长焦距物镜透镜同轴拉曼探针、超级陷波滤波器、ICCD成像光谱仪和半导体绿色激光器组成。利用石墨靶进行了初步实验，发现单壁碳纳米管的拉曼信号中瑞利散射光的抑制特性不足以检测RBM。在拉曼光谱系统的实际应用中，由于加热碳颗粒产生的强黑体辐射干扰了高灵敏度的光学测量，可能需要高灵敏度的脉冲拉曼系统。在所提出的新的CNT合成工艺中，使用甲烷气体、乙醇或丙酮作为碳源，并且通过脉冲Nd：YAG激光器烧蚀催化金属靶如Ni、Co以在反应管中提供催化纳米颗粒。采用He-Ne激光光吸收法监测反应管中碳烟的生成。清楚地观察到烟尘产生的时间行为，并发现工艺条件如碳源、环境气体温度和气体流速的差异。

To investigate CNT properties in real time during CNT synthesis process by a pulsed laser ablation(PLA) method, a compact Raman spectroscopy system was designed and built, which consists of a coaxial Raman probe with an objective lens of long focal length, a super notch filter, an imaging spectroscope with ICCD, and a semiconductor green laser. A preliminary experiment using a graphite target, it was found that rejection property of Rayleigh scattering light was not enough to detect RBM in Raman signal of SWNT. In practical application of the Raman spectroscopy system, since strong blackbody radiation due to heated carbon particles disturb high sensitive optical measurement, a pulsed Raman system with high sensitivity may be necessary.A PLA method was combined with a conventional CVD method for CNT preparation. In the proposed new CNT synthesis process methane gas, ethanol or acetone was used as a carbon source and a catalytic metal target as Ni, Co was ablated by a pulsed Nd:YAG laser to supply catalytic nano-particles in a reaction tube. An optical absorption method using a He-Ne laser was applied to monitor development of carbon soot in the reaction tube. Temporal behavior of soot production was clearly observed and found difference in process conditions such as carbon source, ambient gas temperature, and gas flow rate.