Understanding the stability of a sputtered Al buffer layer for single-walled carbon nanotube forest synthesis

We have clarified the reason that aluminum (Al) buffer layers prepared by sputtering on catalytic substrates are stable for single-walled carbon nanotube forest synthesis on chemical vapor deposition. We have focused on the difference between thermal evaporation and sputtering as the method for the preparation of the buffer layers and have analyzed the Al layers using X-ray photoelectron spectroscopy and transmission electron microscopy. Al layers produced by sputtering strongly suggest the formation of γ-alumina by aluminum hydroxides while those from thermal evaporation contain metallic Al. As a result a drastic structural change occurs during thermal annealing, making the buffer layer unstable.