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The Photoelectric Properties of Oxygen-deficient Mixed-phase TiO2 Nanotube Arrays

Published online by Cambridge University Press:  25 May 2012

Chun-Hsien Chen ,
Jay Shieh  and
Hua-Yang Liao
Chun-Hsien Chen
Affiliation:
Department of Materials Science Engineering, National Taiwan University, Taipei 106, Taiwan
Jay Shieh*
Affiliation:
Department of Materials Science Engineering, National Taiwan University, Taipei 106, Taiwan
Hua-Yang Liao
Affiliation:
Research Center for Applied Sciences, Academia Sinica, Taipei 115, Taiwan
*
*Email: jayshieh@ntu.edu.tw
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Abstract

The photoelectric properties of oxygen-deficient titanium dioxide (TiO2) nanotube arrays are investigated in this study. The TiO2 nanotube arrays are prepared by anodization, followed by annealing at 450 to 750 °C for 3 h in air to form different crystalline phase mixtures. When the annealing temperature is increased, several phenomena are observed: (1) the ratio of anatase to rutile decreases, (2) the anatase nanotubes are shortened and (3) the thickness of the dense rutile film layer underneath the anatase nanotubes increases. The efficiency of visible light absorption of the nanotube arrays is enhanced with increasing annealing temperature. This is believed to be caused by the ionic defects, especially the oxygen vacancies, generated during the annealing procedure, enabling the absorption of low-energy radiations. The X-ray photoelectron spectroscopy (XPS) depth profile analysis provides the supporting evidence on the chemical nonstoichiometry (i.e., oxygen-deficiency) of the TiO2 nanotube arrays annealed at high temperature. With increasing annealing temperature, a decrease and an increase in the photocurrent density of the nanotube arrays under UV and visible light (wavelength > 500 nm) irradiations, respectively, are detected. The decrease of the photocurrent density under UV irradiation is caused by the reduction in the specific surface area (i.e., anatase nanotubes transform into rutile film with vigorous annealing). In contrast, the increase of the photocurrent density under visible light irradiation is contributed to the oxygen vacancies in the nanostructure, providing extra electron energy levels (locating below the conduction band of TiO2) within the band structure.

Keywords

nanostructureabsorptiondefects
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1442: Symposium Q – Titanium Dioxide Nanomaterials––2012 , 2012 , mrss12-1442-q04-03
Copyright
Copyright © Materials Research Society 2012

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