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

为了实时研究脉冲激光烧蚀法合成碳纳米管过程中的性能，设计并构建了一个紧凑的拉曼光谱系统，该系统由带长焦距物镜的同轴拉曼探头、带超陷波滤波器、带ICCD的成像分光镜和半导体绿色激光器组成。在石墨靶上进行的初步实验中，发现对瑞利散射光的抑制性能不足以检测到单壁纳米管拉曼信号中的RBM。在拉曼光谱系统的实际应用中，由于加热碳粒子产生的强黑体辐射会干扰高灵敏度的光学测量，因此可能需要高灵敏度的脉冲拉曼系统。将聚乳酸法与传统的CVD法相结合，制备碳纳米管。在新碳纳米管合成工艺中，以甲烷气体、乙醇或丙酮为碳源，用脉冲Nd:YAG激光烧蚀Ni、Co作为催化金属靶，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内碳烟的形成。清晰地观察了烟尘生成的时间行为，发现了碳源、环境气体温度和气体流量等工艺条件的差异。

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.