Template-directed gas-phase fabrication of oxide nanotubes

This paper describes a template-directed fabricating method of oxide nanotubes. Our approach combines gas-phase atomic layer deposition (ALD) of metal oxides with a micro-contact printing technique, allowing precise control over the dimensions of the nanotubes as well as one-step fabrication of free-standing oxide nanotubes. Nanotubes of TiO2, ZrO2, and Al2O3 with high aspect ratios of up to similar to 300 have been fabricated. Notably, two different types of membranes are employed as templates: track-etched polycarbonate and anodic aluminium oxide (AAO). We have discussed the nanopore size effects in growing ALD layers as nanotube walls and the surface chemistry of selective ALD on the templates. Bundle formation of oxide nanotubes is proposed by strong capillary forces generated and exerted during dissolution of the surrounding AAO template.