Effect of microstructure and crystallinity on the photocatalytic activity of TiO₂thin films deposited by dc magnetron sputtering

Abstract

TiO2 thin films were deposited by dc magnetron sputtering from sub-stoichiometric TiO2−x targets. The as deposited films were XRD amorphous and their microstructure was varied by changing the Ar-pressure and the applied dc power during sputtering. An anneal treatment at 673 K/1 h in air resulted in the crystallization of a preferentially oriented anatase phase, the degree of which depended on the deposition conditions. The microstructure, optical and photocatalytic properties of the thin films were investigated using SEM, UV–VIS spectroscopy and a custom made photocatalytic test reactor, respectively. The thin film density was estimated from their refractive index. Density and crystallinity were the most important factors determining the photocatalytic activity of the thin films.

Quantitative relation between photocatalytic activity and degree of 〈001〉 orientation for anatase TiO2 thin films

“…21 In the case of room temperature deposition, yielding initially amorphous films with varying stoichiometry, growth in the <001> direction can be induced by post-deposition heat treatment. 18,20 This textured growth is an intrinsic property of the films and is unaffected by the type of substrate that is used. 18 We have previously demonstrated that the preferential <001> orientation of the crystal grains in nanostructured films can be controlled by altering the partial oxygen pressure in the deposition chamber during thin-film preparation.…”

“…Several studies have shown that reactive DC magnetron sputtering yields anatase TiO 2 films with preferential orientation along the <001> crystallographic direction. [18][19][20] Depending on the preparation conditions, this orientation might be altered. For example if the films are deposited at high temperature, leading to direct formation of anatase, substrate bias can be used to change the crystallographic orientation.…”

Application of a novel microwave plasma treatment for the sintering of nickel oxide coatings for use in dye-sensitized solar cells

“…NiO x films have been fabricated by various techniques which include spin coating, dipping, electrochemical deposition [17], magnetron sputtering [18][19][20] and sol-gel [21][22][23][24][25]. With the exception of electrochemical techniques, the other deposition methods require subsequent thermal treatments in order to enhance the density of the coatings [21][22][23][24][25][26], to obtain crystalline structure in the as deposited sputtered coatings [26] and to remove the binder in the case of sol-gel deposited coatings [21][22][23][24][25]. Typically sintering conditions of 300-450 °C for 30 to 60 minutes are reported [21][22][23][24][25].…”

Photocatalytic Properties of Doped TiO2 Coatings Deposited Using Reactive Magnetron Sputtering

“…A small broadening and shifting of this peak is seen in the doped coatings, indicating the distortion of the crystal lattice by these dopants. Heat treatment of TiO2 has been reported to increase its crystallinity and photocatalytic performance [25,32]. The coatings in this work were therefore annealed at 600 C in air to investigate the effect on the structure and properties.…”

“…The coatings in this work were therefore annealed at 600 C in air to investigate the effect on the structure and properties. However, an evaluation of the surface topography revealed that heat treatment resulted in the segregation of significant amounts of the co-sputtered material Heat treatment of TiO 2 has been reported to increase its crystallinity and photocatalytic performance [25,32]. The coatings in this work were therefore annealed at 600 • C in air to investigate the effect on the structure and properties.…”