Controllable fabrication of tube-in-tubes using anodic aluminum oxide templates

We have developed a method to fabricate tube-in-tubes that are relatively long and made in all the pores of porous anodic aluminum oxide (AAO) nano-templates. Relatively a very small amount of Co was deposited in the pores of AAO templates prepared without doing a voltage drop at the end of anodization, and then etched in NaOH solution. This caused the carbon nanotubes (CNTs) to grow out from all the pores, and larger diameter carbon nanotubes were also made on the inner surface of all the pores, by forming tube-in-tubes. We were able to control the gap between the inner surface of the larger tubes and the outer surface of the smaller ones of tube-in-tubes in some range by changing the etching time in NaOH solution. Tube-in-tubes that are relatively long and controlled the gap could be used as a storage, particularly for hydrogen gas. (C) 2003 Elsevier B.V. All rights reserved.