Optimization of CNTs growth on TiB₂-based composite powders by CVD with Fe as catalyst

Carbon nanotubes (CNTs) are successfully grown on the surface of TiB₂ matrix by chemical vapor deposition with Fe as catalyst. However, CNT growth has to be improved before conducting integration procedures. The effects of synthesis conditions on the structure of CNT(Fe)–TiB₂ are evaluated by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. Results indicate that with an increase in synthesis temperature, carbon yield increases because of the improvement in the initial growth rate of CNTs. The morphology of as-received carbon changes due to changes in surface roughness of TiB₂. With an increase in Fe catalyst, the density and diameter of carbon particles increase as well because of the increased number of activity sites and agglomeration of Fe particles. As the gas flow rate of methane supply rises, the density and length of CNTs initially increase and then decrease. This behavior is attributed to the increase in carbon diffusion rate and decrease in contact time between the catalyst and the carbon precursor. As growth duration is extended, CNT growth initially improves because of the sufficient reaction time between the carbon precursor and the catalyst. However, the quality of CNTs subsequently decreases, and a large amount of amorphous carbon is produced owing to the aggregation of the carbon precursor, which leads to excessive concentration of Fe.