Evaluation of ion and radical fluxes in CH4/H2 plasma for CNT growth

Abstract

A CH4/H2 radio frequency capacitively coupled plasma used for synthesis of carbon nanotubes (CNTs) was simulated with a 1-dimensional fluid model. The pressure of CH4 was fixed at 1 Torr and that of H2 varied from 0 to 9 Torr. When the H2 mixture ratio was 0.1, the fluxes of H2+ and H3+ to the substrate were respectively about 5 and 10 times those for the case without H2 mixing. In our previous experiment, a slight mixture of H 2 promoted CNT growth. We inferred that this was because H 2 maintained the activity of the catalyst particle from which CNT grew. The present numerical result supports our hypothesis. In addition, C xHy(x, y≥2) accumulated with time. This accumulation is not negligible because it lowers the electron temperature. We estimated the H2 ionization rate in CH4/CxHy is about 2/3 of that in CH4. It is pointed out that we need to consider the accumulation of CxHy to improve the accuracy of the estimation of CNT growth. © 2008 The Institute of Electrical Engineers of Japan.