ALD for Functional Devices Based on TiO2 Nanotube Arrays

Abstract

Synthesis of highly-ordered nanostructures of valve metal oxides has recently attracted huge scientific and technological interest motivated by their possible use in many applications. It is the nanotubular TiO2 that has received the highest attention after porous Al2O3, motivated by its wide range of applications, including photo-catalysis, solar cells and biomedical uses. However, the TiO2 nanotube potential for a range of advanced devices, in particular when considering all possible shapes and geometries, has not at all been exploited. One of the major issues to extend the functional range of nanotubes is to coat homogenously tube interiors by a secondary material, potentially until the complete tube filling. Efforts based on electrochemical deposition, chemical deposition and spin-coating led only to limited success with a narrow range of materials. The presentation will therefore focus in detail on the coating of secondary materials inside the nanotubes by means of ALD. The deposited materials influence strongly optical, electrical and mechanical properties of nanotubes. Experimental details and some very recent results demonstrating unprecedented ability of nanotube functionalization by ALD will be presented and discussed [1-3].