Fabrication of metal oxide coaxial nanotubes using atomic layer deposition

We fabricated nanotubules of TiO ₂ and ZrO ₂ using atomic layer deposition (ALD) technique with polycarbonate (PC) nanoporous filters as a template. Alkylsiloxane monolayers on the both sides of PCs were formed by blanket type contact printing in order to achieve one-step process of the freestanding oxide nanotubes. TiO ₂ and ZrO ₂ nanotubes with 30-200 nm of diameter were successfully fabricated by ALD at 140°C and subsequent chemical etching of the PC. Very high aspect ratio of 160:1 was achieved in both oxide nanotubes. Growth rates of the wall thickness in oxides nanotubes were 0.5 and 0.6 Å/cycles for 200 and 50 nm pore sizes of PC templates, respectively, showing ultra-precise control of the wall thickness, so as to inner diameter of the tubes. Prepared oxide nanotubes were characterized by high-resolution transmission electron microscopy (HR-TEM), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). Oxide nanotubes were filled with CdS using chemical bath deposition (CBD). We successfully demonstrated formation of coaxial TiO ₂/CdS nanocables. Further we developed MO-CVD processes for Cu layer. As a result, coaxial nanotubes of TiO ₂/Cu and ZrO ₂/Cu were successfully fabricated. Combination of the ultra-precise wall thickness control of oxide nanotube with high-aspect ratio filled Cu layer provides us a possible quantum coaxial cable for nanoelectronic applications.