Fabrication of Metal Oxide Coaxial Nanotubes Using Atomic Layer Deposition Daekyun Jeong 1 , Taekwan Oh 1 , Hyunjung Shin 1 , Woo-Gwang Jung 1 , Jaegab Lee 1 , Myung Mo Sung 2 and Jiyoung Kim 1,* 1. School of Advanced Materials Engineering, Kookmin University, 2. Department of Chemistry, Kookmin University Seoul, 136-702, Korea, * jiyoung@kookmin.ac.kr ABSTRACT 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 140ºC 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. Keywords: Nanotube, Self-Assembled Monolayers, Atomic Layer Deposition, Template, Wall thickness 1 INTRODUCTION Metal oxide nanotubes as well as CNTs [1] are expected to be useful for various applications such as nanoelectronics, biological sensors, nano-fluidic devices, nano- electromechanical system (NEMS) and energy storage, etc [2]. Particularly, one-dimensional structures of inorganic materials have attracted a lot of attention because of their unique properties (e.g., electronic, magnetic, optical, etc.) and potential applications in the near future In this study, we reported that more controllable and feasible process for nanotube of TiO 2 as well as ZrO 2 using atomic layer deposition (ALD) and nanoporous poly- carbonate (PC) membrane as a template.[3] We reported that the formation of TiO 2 and ZrO 2 nanotubes by ALD oxide thin film[4] coating on the nanoporous membranes (commercially available polycarbonate filters) as templates and subsequently removing the templates.[5] Applying this method, we successfully developed novel fabrication routes for coaxial nanotubes of metal oxides with metal oxide nanotubes with semiconducting CdS core as well as metallic Cu layer. 2 EXPERIMENTAL Fig. 1 shows the schematic flow of the fabrication process of the oxide nanotubes in this study. Membranes used in this study as nano-templates are hydrophilic poly- carbonate (PC) filters. The PC filters are commercially available (Whatman Co., UK). PC filters used in this study have nano-pores of diameter of 200 nm, 50 nm, or 30 nm. The pores in these filters are randomly distributed across the filter, and pore densities are approximately 3 10 8 pores/cm 2 . Coatings on inner wall of PC filters were carried out using ALD up to 140 C. Self-limiting surface reaction in our home-made ALD processes for thin films of TiO 2 and ZrO 2 were confirmed up to 200 C. Above 140 C, the PC filters were distorted due to the thermal stress in ALD reaction chamber. Therefore process temperatures for oxide nanotube fabrication were kept lower than 140 C. Zirconium t-butoxide and Titanium iso-propoxide were used as sources of Ti and Zr. Water vapor with the flow rate of 5 sccm was used as an oxidant. N 2 was used as a carrier gas and Ar gas was used for purging. A cycle of ALD includes Zr and/or Ti source/purging/H 2 O(g)/purging (e.g. 2/80/2/240 sec., respectively, in case of ZrO 2 coating). Growth of TiO 2 thin films with 0.4 Å/cycle at 150 C can be achieved. In a typical experiment, 100 ~ 800 cycles of ALD were performed to synthesis nanotubes of TiO 2 and ZrO 2 . After the desired cyclic ALD processes, the PC filters were etched away using the solution of chloroform at 60 C. NSTI-Nanotech 2005, www.nsti.org, ISBN 0-9767985-1-4 Vol. 2, 2005 638