Effects of a SiO 2 sub-supporting layer on the structure of a Al 2 O 3 supporting layer, formation of Fe catalyst particles, and growth of carbon nanotube forests

We investigate the effects of a SiO 2 sub-supporting layer on the growth of carbon nanotube (CNT) forests, especially on the spinnability of the CNT forest into a CNT yarn, which is one of the most promising application areas based on CNTs as a light-weight, strong, and electrically and thermally conductive macro-scale material. So far, most spinnable CNT forest growths have been performed using Fe/Al 2 O 3 deposited on a Si wafer with a thermally grown SiO 2 layer. However, only a few studies have focused on examining the effects of the SiO 2 sub-supporting layer on the growth and spinnability of CNT forests by microscopic analyses. Herein, using atomic force microscopy (AFM), transmission electron microscopy (TEM), liquid contact angle, and ellipsometry measurements, we demonstrate that the presence of a SiO 2 sub-supporting layer significantly affects the structure of Al 2 O 3 , adhesion between Al 2 O 3 and Fe layers, and the number density of Fe catalyst particles, thereby strongly affecting the growth and spinnability of CNT forests. This study opens up new possibilities for accurately controlling the growth of CNT forests by proper designing of the sub-supporting layers.