Measurement of carbon plasma plume for optimization of the process carbonaceous functional materials

利用KrF准分子激光（λ=248 nm）和Nd：YAG激光（λ=532 nm）在真空中烧蚀石墨靶产生碳等离子体羽流。用二维激光诱导荧光法、光谱吸收法和离子探针法测量了C_2分子、C原子和C^+的相对密度及其分布。实验结果如下：1）KrF激光烧蚀石墨时，C原子和离子处于高电子激发态。随着激光能量密度的增加，离子数增加，烧蚀后100 ns内发生辐射复合。2）Nd：YAG激光产生的等离子体羽中C，C^+的辐射。3）烧蚀后300 ns，KrF等离子体羽流中C_2分子的温度约为2,870 K，高于Nd：YAG等离子体羽流中的温度。Nd：YAG基频激光加热蒸发石墨靶产生C、C^+、C_2等离子体，在500 Torr Ar气中，用Nd：YAG激光（λ=532 nm）烧蚀含Ni的石墨复合棒形成碳纳米管的等离子体羽流的光学测量。观察到Ar、Ni等原子的多条发射谱线，并伴有C、C_2、C^+、C^<2+>的发射。烧蚀后400 ns，碳原子的发射基本消失，而Ni原子的发射持续时间较长，说明Ni原子处于激发态。激光Mie散射图像显示，烧蚀后几百μs左右，碳颗粒在靶附近形成，并以7 m/s的初速度漂移，在几十ms内扩散形成漩涡。

Carbon plasma plumes are produced by ablating a graphite target using KrF excimer laser (λ=248 nm) and Nd:YAG laser (λ=532 nm) in vacuum. Relative densities and their profiles of C_2 molecules, C atoms and C^+ were measured using 2D-LIF, spectral absorption method and ion probe method. Experimental results are summarized as follows.1) C atoms and ions ejected from a graphite by KrF laser ablation are in highly electronically excited states. Number of ions increases with increase of laser fluence and they play radiative recombination within 100 ns after ablation.2) Emission from plasma plume produced by Nd:YAG laser from C, C^+. The number of C, C^+, C_2 increase with laser fluence.3) Temperature of C_2 molecules in KrF plasma plume is about 2,870 K at 300 ns after ablation, which is higher than that of Nd:YAG plasma plume. Production of C, C^+, C_2 by Nd:YAG fundamental laser results from heating and evaporation of a graphite target.Optical measurement of plasma plume under carbon nanotubes formation condition, where a graphite composite rod containing Ni was ablated by Nd:YAG laser (λ=532 nm) in 500 Torr Ar gas. Many atomic emission lines of Ar, Ni were observed with emission from C, C_2, C^+, C^<2+>. Most of emission from carbonaceous species extinguish at 400 ns after ablation, however, Ni atomic emission lasts for long time and it indicates existence of excited Ni atoms. Laser Mie scattering images showed that carbon particulates are formed near the target at about several hundreds μs after ablation and drift at initial velocity of 7 m/s and diffuse forming swirls few tens ms.