Growth of Ultra-High Density Vertically-Aligned Carbon Nanotube Forests

We present a general catalyst design method to synthesise ultra-high density, aligned forests of carbon nanotubes by cyclic deposition and annealing of catalyst thin-films. This leads to nanotube forests with an area density of at least 10$^{13}$ cm$^{-2}$, over one order of magnitude higher than existing values (Hata 2004, Zhong 2006), and close to the limit of a fully dense forest. The technique consists of cycles of ultra-thin metal film deposition, annealing, and immobilisation. The nanotubes are then grown as normally by Chemical Vapor Deposition. These ultra-dense forests are needed to use carbon nanotubes as vias and interconnects in integrated circuits and as thermal interface materials. Further density increase to 10$^{14}$ cm$^{-2}$ by reducing nanotube diameter is possible.