Hydrogen plasma treatment on catalytic layer and effect of oxygen additions on plasma enhanced chemical vapor deposition of carbon nanotube

摘要

Multi-wall carbon nanotubes have been synthesized by plasma enhanced chemical vapor deposition (CVD) on Co-coated silicon substrates. Prior to the deposition of carbon nanotubes, dense and uniform nanosized catalytic seeds were formed by hydrogen plasma treatment on Co thin film. The size and morphology of Co catalytic seeds varied with hydrogen plasma treatment time. In the carbon nanotube growing process, a mixture of Ch_4 and H_2 was used as gas source. Small O_2 additions to the CH_4-H_2 gas mixture (0-12 percent of mixture gas) improved the purity of carbon nanotubes and surprisingly led to high quality even at low growth temperature (610 deg C) as observed in high-resolution transmission electron microscopy (HRTEM). In order to understand the growth process by CH_4-H_2-O_2 plasma CVD in detail, optical emission spectroscopy (OES) was introduced. The results of OES analysis showed that, with the increase of oxygen amount, the intensity of C_2 decreased gradually, but the intensity of the OH radical increased sharply. It probably leads to increasing the etching effect on defective structure by affluent OH radical and suppressing super-saturation of carbon molecules at growing edges.