Gd-Enhanced Growth of Multi-Millimeter-Tall Forests of Single-Wall Carbon Nanotubes

Multi-millimeter-tall vertically aligned single-wall carbon nanotube (VA-SWCNT) forests were grown using Fe/Gd/Al₂O catalyst with high initial growth rate of ∼2 μm s^-1 and long catalyst lifetime of ∼70 min at 800 °C. The addition of Gd with a nominal thickness of 0.3 nm drastically prolonged the catalyst lifetime. The analysis of the VA-SWCNT forests by a transmission electron microscope showed that the average diameter of the SWCNTs grown with Gd is constant from the top to the bottom of the forests, while it monotonically increased without Gd. This indicated that Gd suppresses the structure change of the Fe nanoparticles in the lateral direction during the CNT growth. By X-ray photoelectron spectroscopy, it was found that the longer catalyst lifetime with Gd stems from the suppression of the interaction between Fe and C resulting in the smaller structure change of the Fe nanoparticles.