Enhanced growth of ultra-high density carbon nanotube forests via Fe and Al vapor addition in a CVD process

Carbon nanotube (CNT) forests suffer from a pronounced density decline as their length increases, primarily due to diminishing catalytic activity during growth. Here, we report a vapor-phase synthesis strategy incorporating Fe and Al additives that yields CNT forests with substantially higher densities than those produced by conventional methods. Notably, CNT forests with a height of 1.3 mm achieved a mass density of 149 mg/cm 3 —the highest reported for forests exceeding 1 mm in height. This improvement is attributed to the prolonged lifetime of catalyst particles afforded by the synergistic effects of Fe and Al, which effectively suppress density decay during growth. Moreover, we investigated the electrical resistivity of these ultra-high-density CNT forests to elucidate their macroscopic conduction properties. This approach overcomes the intrinsic limitations of density decay and opens new opportunities for integrating CNT forests into advanced device technologies.