Structure-controlled growth of vertically-aligned carbon nanotube forests using iron–nickel bimetallic catalysts

Although the progress towards catalyst engineering and growth parameters to tune the properties of carbon nanotubes have been widely studied, critical properties like chirality still need addressing in the case of bimetallic catalysts. Herein, we synthesized six different catalysts via solid-state reactions using a mechanical alloying (MA) method to investigate the role that these catalysts have in the growth of high-quality vertically aligned carbon nanotubes (VACNTs). The growth of the VACNTs was performed using a chemical vapor deposition method onto silicon wafers. Focusing on the impact of Ni addition into the Fe matrix, we explored the diameter distribution and chirality profiles of the VACNTs. The conductive band branches, the overall mapped morphology, chemical purity, structural quality, and physical alignment of the VACNTs were analysed in detail using Raman micro spectroscopy, thermogravimetric analysis, and scanning electron and transmission electron microscopies. The relative radial breathing modes were explored for the (12,3), (9,3), (9,6), and (10,4) chiralities, with different counts for overall samples. Furthermore, the (11,9) chirality index, which is the most encountered type by far, was observed in the synthesis of VACNTs on the Fe50Ni catalyst, with a relatively high count of 28%. The current Fe–Ni bimetallic catalyst study thus employs Raman spectroscopy to determine the role that Ni addition into the Fe matrix has in the possible difference in the conductive branches of the VACNTs.