The effect of sputtering gas pressure on structure and photocatalytic properties of nanostructured titanium oxide self-cleaning thin film B. Abdollahi Nejand a , S. Sanjabi a, * , V. Ahmadi b a Nanomaterials Group, Dept. of Materials Engineering, Tarbiat Modares University, P.O.Box: 14115-143, Tehran, Iran b School of Electrical and Computer Engineering, Tarbiat Modares University, P.O.Box: 14115-143, Tehran, Iran article info Article history: Received 9 March 2010 Received in revised form 23 May 2010 Accepted 2 August 2010 Keywords: Nanostructured TiO 2 thin films Sputtering Structure Photocatalytic activity abstract Titanium oxide thin films were deposited by DC reactive magnetron sputtering on ZnO (80 nm thick- ness)/soda-lime glass and SiO 2 substrates at different gas pressures. The post annealing on the deposited films was performed at 400  C in air atmosphere. The results of X-ray diffraction (XRD) showed that the films had anatase phase after annealing at 400  C. The structure and morphology of deposited layers were evaluated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The surface grain size and roughness of TiO 2 thin films after annealing were around 10e15 nm and 2e8 nm, respectively. The optical transmittance of the films was measured using ultravioletevisible light (UVevis) spectrophotometer and photocatalytic activities of the samples were evaluated by the degradation of Methylene Blue (MB) dye. Using ZnO thin film as buffer layer, the photocatalytic properties of TiO 2 films were improved. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Organic and inorganic pollutants are the agents of air and water contamination. Many studies have concentrated on the develop- ment of photocatalytic materials as a method to breakdown and remove these pollutants [1e5]. One of the most popular photo- catalysts is TiO 2 , which has been investigated widely from 1972 [6]. The degradation mechanism by photocatalytic phenomena can be explained by delocalization of the electrons and production of pairs of electron and holes. The generated electronehole pairs can degrade the existing hazardous contaminations in air and water [2e5] mostly under UV light [7,8]. For the anatase crystalline phase of titanium dioxide, the minimum energy for starting photo- degradation must exceed the 3.2 eV band gap in order to generate electronehole pairs [9]. To achieve more efficient photocatalytic activity and enhance transparency, thin films have been utilized [1,10,11]. DC reactive magnetron sputtering is one of the popular methods to fabricate the uniform and columnar thin films at low substrate temperatures [12e14]. The morphology and the microstructure of the formed TiO 2 films are affected by sputtering parameters such as gas pres- sure, substrate and target temperatures, power supplied, partial pressure of reactive gases, angle of deposition, distance between the target and substrate, and the purity of targets and gases. Of these, sputtering gas pressure can have a significant influence on struc- ture, morphology and formed phases. A few studies have reported on the deposition of TiO 2 films in low sputtering pressures [12,15]. In this study, TiO 2 /ZnO thin films were prepared by a DC reactive magnetron sputtering under different sputtering gas pressures. The effect of deposition gas pressure on the appearance of the film’s surface, phase formation, optical properties and photocatalytic activities have been investigated. Since the transparency of the fabricated layers on glass is of great importance, this work is focused mainly on the surface morphology and roughness, which are directly related to the amount of transmitted light. To investi- gate the photocatalytic activity of the fabricated thin films, effect of deposition pressure on degradation of MB dye and hydrophilicity of thin films were studied. ZnO was chosen as a buffer layer because of its high transparency, it has a similar band gap to TiO 2 thin films, its potential to alter the growth of TiO 2 , and to prevent the diffusion of sodium and calcium ions into TiO 2 thin films from the soda-lime glasses [16e18]. 2. Experimental procedure 2.1. Deposition procedure TiO 2 thin films were deposited by a reactive DC magnetron sputtering on soda-lime glass and SiO 2 substrates at 100  C. The * Corresponding author. Tel.: þ98 21 82883325; fax: þ98 21 88005040. E-mail address: sanjabi@modares.ac.ir (S. Sanjabi). Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2010.08.001 Vacuum 85 (2010) 400e405