Formation of SWCNTs in arc plasma: Effect of graphitization of Fe-doped anode and optical emission studies

Fe-doped (ca. 1 at%) homogeneous graphite electrodes (with different graphite microcrystallites, degree of graphitization and, thereby, electrical conductivities) were used to produce single-walled carbon nanotubes (SWCNTs) in Ar/Kr/Xe-H-2 arc plasma under pressure equal to 26 kPa. The use of electrode with the smaller primary particle size (about 5 nm) comparing to the well-graphitized electrode (25 nm) drastically increased the yield of SWCNTs in Ar-H-2 arc plasma, while plasma parameters (temperature, C-2 content, and namely carbon vapor pressure) remained on similar levels. However, the use of electrodes with larger grain size (25 nm) can lead to SWCNTs growth when they are arc ablated under the presence of Kr (or Xe)-H-2 gas mixture. Thus, the mechanism of CNT formation seems to be more complex that the one involving only simple carbon species (e.g., C-2).