Simple and engineered process yielding carbon nanotube arrays with 1.2 × 10¹³ cm^-2 wall density on conductive underlayer at 400 °c

A simple process is presented that realizes carbon nanotube (CNT) arrays that meet the process and structure requirements for use in large-scale integrated circuits. Ni particles are formed densely on a conductive TiN layer on SiO₂/Si substrates through nucleation and growth by sputtering, which was stopped prior to percolation of the Ni particles. Ni particles as dense as 2.8 × 10¹² cm^-2 were formed after annealing at 400 °C and chemical vapor deposition (CVD) was carried out at 400 °C by feeding C₂H₂ at partial pressures as low as 0.13-1.3 Pa so as not to kill the catalyst. Scanning electron microscopy with energy dispersive X-ray spectroscopy revealed the mass density of the arrays to be as high as 1.1 g cm^-3. High resolution transmission electron microscopy showed the densely packed CNTs with an average wall number of eight. Atomic force microscopy of the root of the CNT arrays transferred to a SiO₂/Si substrate enabled direct counting of individual CNTs, revealing areal densities of CNTs and CNT walls as high as 1.5 × 10¹² and 1.2 × 10¹³ cm^-2, respectively. The simple process, using conventional sputtering and CVD apparatus, with carefully engineered conditions offers a route for practical application of CNTs.