Effects of H_2 plasma pretreated Ni catalysts on the growth of carbon nanotubes

摘要

Presented in this study are the effects of pretreatment temperature during H_2 plasma on synthesizing the multi-walled carbon nanotubes (MWCNTs) by using the microwave plasma chemical vapor deposition (MPCVD). A H_2 and CH_4 gas mixture with a 9:1 ratio was used as a precursor for the synthesis of MWCNTs on Ni-coated TiN/Si (100) 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 H_2 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 H_2 plasma. In addition, TEM results suggest that H_2 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.