Effects of H2 plasma pretreated Ni catalysts on the growth of carbon nanotubes

Presented in this study are the effects of pretreatment temperature during H2 plasma on synthesizing the multi-walled carbon nanotubes (MWCNTs) by using the microwave plasma chemical vapor deposition (MPCVD). A H2 and CH4 gas mixture with a 9:1 ratio was used as a precursor for the synthesis of MWCNTs on Ni-coated TiN/Si (1 0 0) substrates. The structure and composition of Ni catalyst nanoparticles were investigated using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM) techniques. The present findings showed that denser Ni catalyst nanoparticles and more vertically aligned MWCNTs could be effectively achieved at higher pretreatment temperature during H2 plasma. The results of Raman spectra and TEM indicate that the morphologies of MWCNTs transform from amorphous carbon to a crystalline graphite structure or finite-sized graphite structure, depending on the pretreatment temperature during H2 plasma. In addition, TEM results suggest that H2 plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles. A decrease in the number of defects and optimized morphologies therefore is believed to play a significant role in improving the field-emission characteristics observed in the future.