Search

The present work is investigating the photocatalytic activity of TiO 2 thin films deposited by radiofrequency magnetron sputtering of a pure TiO 2 target in Ar and Ar/H 2 O (pressure ratio 40/3) plasmas. Optical absorption, structure, surface morphology and chemical structure of the deposited films were comparatively studied. The films were amorphous and included a large amount of hydroxyl groups (about 5% of oxygen atoms were bounded to hydrogen) irrespective of the intentional content of water in the deposition chamber. Incorporation of hydroxyl groups in the film deposited in pure Ar plasma is explained as contamination of the working gas with water molecules desorbed by plasma from the deposition chamber walls. However, intentional input of water vapour into the discharge chamber decreased the deposition speed and roughness of the deposited films. The good photocatalytic activity of the deposited films could be attributed hydroxyl groups in their structures. [ABSTRACT FROM AUTHOR]

Abstract: The photocatalytic chemisorption of water on titanium dioxide (TiO2) thin films was studied by photocurrent decay experiments on the films exposed to water vapour. The TiO2 films were deposited on quartz substrates by sputtering of a high purity TiO2 target in a radio frequency magnetron discharge in argon–oxygen gas. In vacuum (10-2Torr), the films with good photocatalytic activity had large induced photocurrent intensity and long electrical charge carrier lifetime, when compared to the films with low photocatalytic activity. The photocurrent decay in good photocatalytic films exposed to water–argon gas mixture at atmospheric pressure depended strongly on the gas humidity, larger decay rates being observed at larger humidity values. Because of the oxygen chemisorption, the photocurrent decay rates were larger in air than in the same humidity water–argon gas. [Copyright &y& Elsevier]

Atomic force microscopy (AFM) measurements of the tip–sample friction and adhesive forces were used to study the chemical homogeneity of the surface of titanium dioxide thin films deposited by radio frequency magnetron sputtering deposition. As a result of the photocatalytic activity, the film surface turned superhydrophilic by UV light irradiation in air. However, the AFM measurements showed that the surface of titanium dioxide deposited at low gas pressure (1 mTorr) was chemically heterogeneous with grains of very low photocatalytic activity. In the ambient air, due to the capillary condensation of the water vapor at the AFM tip–sample contact, the superhydrophilic regions on the film surface show larger friction and adhesive forces compared to the regions of low hydrophilicity. [ABSTRACT FROM AUTHOR]

This paper reports results of the macroscopic and microscopic studies of the UV-light-induced hydrophilicity of TiO2 thin films prepared by radio frequency magnetron sputtering of a pure TiO2 in an Ar–O2 mixture gas at different pressure values. The gas pressure affects the crystallographic structure as well as the surface topography and UV-light-induced hydrophilicity of the deposited films. The microscopic study of the film hydrophilicity is based on friction force microscopy measurements, which are used to microscopically distinguish regions of different hydrophilicity on the film surfaces. These measurements make use of the observation that for a hydrophilic tip, the more hydrophilic the sample surface is, the larger the tip–sample friction force is. The films deposited at a relatively high value of gas pressure (10 mtorr) had an amorphous structure, a good UV-light-induced hydrophilicity and a microscopically smooth and homogeneous surface. The films deposited at lower gas pressure values had mixed crystalline and amorphous structures and relatively rough and inhomogeneous surfaces. The effect of the gas pressure on the plasma particle bombardment of the growing films is discussed to account for the dependence of the structure and surface properties of the films on the gas pressure. [Copyright &y& Elsevier]

The UV-light-induced hydrophilicity of amorphous titanium dioxide thin films obtained by radio frequency magnetron sputtering deposition was studied in relation with film thickness. The effect of UV light irradiation on the film hydrophilicity was fast, strong and did not depend on substrate or thickness for films thicker than a threshold value of about 12 nm, while for thinner films it was weak and dependent on substrate or thickness. The weak effect of UV light irradiation observed for the ultra-thin films (with thickness less than 12 nm) is explained based on results of measurements of surface topography, UV-light absorption and photocurrent decay in vacuum. Comparing to thicker films, the ultra-thin films have a smoother surface, which diminish their real surface area and density of defects, absorb partially the incident UV light radiation, and exhibit a longer decay time of the photocurrent in vacuum, which proves a spatial charge separation. All these effects may contribute to a low UV light irradiation effect on the ultra-thin film hydrophilicity. [Copyright &y& Elsevier]