Photocatalytic and optical properties of nanocomposite TiO₂-ZnO thin films

¹ Physics Department, College of Science, Qassim University, P.O. 6644, 51452 Buryadh, Kingdom of Saudi Arabia
² Physics Department, Faculty of Science, Sohag University, 82524 Sohag, Egypt
³ Physics Department, Faculty of Science, Helwan University, 11792 Helwan, Cairo, Egypt

^a e-mail: abo_95@yahoo.com

Received: 6 August 2011
Revised: 16 October 2011
Accepted: 4 January 2012
Published online: 30 January 2012

Abstract

Nanocomposite TiO₂-ZnO thin films, with different ZnO content, were deposited by electron-beam evaporation on glass and Si(1 0 0) substrates. The resulting films were annealed in air for 1 h at 450 °C. X-ray diffraction revealed the presence of monoclinic β-TiO₂ and hexagonal ZnO for the films prepared with ZnO content of 0 at.% and 100 at.%, respectively. Mixed monoclinic β-TiO₂ and hexagonal ZnO phases were observed at higher ZnO content between 50 at.% and 85 at.%. Spectroscopic ellipsometry (SE) was employed to determine the film thickness and optical constants. A two-layer model was used to describe the experimental ellipsometric data. At any wavelength longer than 390 nm, the refractive index decreases gradually with increasing ZnO content in the composite films. The optical band gap increased with increasing ZnO content. The photocatalytic behavior of TiO₂-ZnO thin films was mainly evaluated by measuring the decomposition of methylene blue. The nanocomposite film with ZnO content of 8 at.% has the best photocatalytic activities.