Rutile TiO2 thin films growth on glass substrates with generation of high entropy interface

Abstract

TiO2 thin films obtained through Reactive Magnetron Sputtering (RMS) have been extensively studied in the last decades for several applications as photocatalyst and self-cleaning coats. However, reactive deposition through MS onto large area substrates can be troublesome due to inhomogeneous films thickness and poor adhesion between film and substrate. This paper investigates the deposition of TiO2 thin films on glass substrates through a two steps method, namely: 1- deposition of nanometer thickness Ti metallic films on glass substrate, through triode magnetron sputtering; 2- oxidation of the Ti film through thermal treatment in atmospheric air, to obtain stoichiometric TiO2 layers. The film oxidation was performed concomitantly to the glass thermal treatment carried out at 650 °C. Analysis through XPS depth profile indicates the formation of a chemically graded high entropy interlayer due to the interdiffusion of atoms from substrate to film and vice-versa, during the thermal treatment. The high entropy interface layer contributes to reduces the mismatch between the film and the substrate lattice, resulting in an improvement of film adhesion. The badgap analysis through Tauc method show two energy values, namely 3.2 eV and 2.9 eV, which can be attributed to TiO2-rutile layer and the high entropy zone at interface, composed by [Ca-Na-Si-Ti]Ox oxides. The wettability results show that the contact angle may be as low as 10° between a deionized water drop and the rutile-TiO2 surface, after activation with UV light irradiation, which is characteristic of super-hydrophilic surface.