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

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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.