The Differences in Optical Characteristics of TiO2 and TiO2/AAO Nanotube Arrays Fabricated by Atomic Layer Deposition

Abstract

Self-aligned TiO2 nanotube arrays can be fabricated by atomic layer deposition (ALD) and anodic oxide template (AAO) on Si or quartz substrates. In this study, we compare the hetero-junction effects on optical characteristics of TiO2 nanotube arrays for the cases with AAO stayed intact and after AAO was etched away selectively. Due to the space confinement effect that can occur only in the TiO2/AAO nanotubes, the photoluminance intensity of TiO2 material is enhanced about 5 times for TiO2/AAO nanotubes compared with the TiO2 nanotubes. On the contrary, under 0 V bias, quantum efficiency of the TiO2/AAO nanotubes is 5.8 times lower than the TiO2 nanotubes because of higher probability for the recombination of photon-generated electron-hole pairs from the space confinement effect in TiO2/AAO nanotube arrays. When the bias reached 1 V, the TiO2 nanotubes still revealed more outstanding photon-to-electron transformation properties than the TiO2/AAO nanotubes. However, the quantum efficiency of TiO2/AAO nanotubes began to exceed TiO2 nanotubes when the bias is over 2 V. This phenomenon could result from the restraint of the recombination of photo-generated electron-hole pairs under high field strength and the increase in an amount of photo-generated carriers injected from AAO template. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.045205jes]