Preparation of TiO 2 thin films by RF magnetron sputtering method and their photocatalytic properties

Abstract

Low-temperature preparation of the TiO 2 thin films was examined by using a RF magnetron sputtering method. TiO 2 films of anatase structure were prepared on the non-heated glass substrates. The photocatalytic properties of films were superior in the films prepared under the sputtering atmosphere of 10 Pa rather than 5 Pa. They showed high activities in the organic material-resolution characteristics. They also had high activity in the hydrophilicity characteristics. Keyword: TiO 2 thin films, RF magnetron sputtering, photocatalyst, low temperature preparation 1. INTRODUCTION TiO 2 films have been focused as a photocatalyst. They have remarkable properties, for example, to resolve organic pollutant and to give hydrophilicity by irradiating near ultraviolet light. These characteristics are used in the fields of antifouling, antifog, sterilization and self cleaning. 1 The photocatalytic reaction of titanium oxide (TiO 2) films occurs only under the irradiation of ultraviolet light. Therefore, the photocatalytic properties under visible light irradiation have been widely investigated recently. In the future, various applications of photocatalysts will be developed. To use the TiO 2 films as a photocatalyst, it must be immobilized on a substrate. For this purpose, low temperature preparation methods with large area and strong adhesion have been desired. 2 The immobilization techniques include wet processes of sol-gel and spray methods, and dry processes of sputtering and ionized cluster beam methods. 3 It is possible to prepare large area with strong adhesion by using a sputtering method. Moreover, a RF magnetron sputtering method is possible for low temperature preparation compared with other sputtering methods because the confinement of electrons and the cathode-drop voltage of high-energy charged-particle are low. TiO 2 has crystal structures of rutile, anatase and brookite. The anatase has the highest photocatalytic activity. This is due to the difference of their band structures. The bandgap of anatase is 3.2 eV, so it is 0.2 eV bigger than that of rutile. The reduction of the oxygen of the anatase is easier than a rutile structure. Also, because the grain size of the anatase structure is smaller than that of rutile, a large area induces higher activity.Therefore, for the photocatalytic reaction, it is possible to say that the anatase type TiO 2 is superior to other structures.