Technological Features of Increasing Photocatalytic Activity of TiO<sub>2</sub> Films Produced by the Reactive Magnetron Sputtering
Introduction. At the current stage of the development of instrumentation, much attention focuses on the technologies for producing films of metal oxides in order to create materials for the production of new generations of elements of information and measuring equipment (UV receivers, gas concentration sensors, etc.). Most of these applications are based on photoexcited processes, which include the photocatalytic effect, superhydrophilicity and internal photoelectric effect. In this field, among metal oxide films there is a great interest in titanium oxide (TiO2) films, which are characterized by high chemical and thermal stability, as well as the possibility of their production by many technologies. In addition to this, TiO2 has a band gap of 3.2 eV, which corresponds to the near UV range, therefore, it is relatively easy to initialize photoinduced processes. The range of applications of TiO2 films is quite wide: from solar energy to various instrumentation fields, including the antireflection coatings of lenses and transparent conductive contacts of solar panels. TiO2, due to its high photocatalytic properties, is used for the decomposition of organically complex compounds. Nevertheless, at the current stage of the development of TiO2 film formation technologies, the dependencies linking the photocatalytic properties with the technological parameters of film production have not been studied yet. The aim of the research is to increase the photocatalytic activity of TiO2 films by changing the ratio of oxygen and argon in the working mixture during the production of films by reactive magnetron sputtering. To achieve the goal, the following tasks were solved: production of a series of TiO2 films by reactive magnetron sputtering at different ratios of oxygen and argon in a vacuum chamber, study of the photocatalytic activity of the produced films under the UV radiation, development of technological recommendations for the optimal ratio of argon and oxygen in the process of production of photocatalytic TiO2 films by reactive magnetron sputtering. Conclusions. Experimental series of TiO2 films was produced at different ratios of argon and oxygen in the chamber with the use of upgraded UVN-71P3 facility by the method of reactive magnetron sputtering. The films exhibited high transmittance and the presence of interference minima and maxima in the studied range. TiO2 films obtained by reactive magnetron sputtering have high photocatalytic properties. Comparison of the average transmittance of film samples with a dye applied before and after UV radiation showed that the transmittance of the substrate without a TiO2 film didn’t change and with a titanium oxide film the value increased by 8-25%. Experiment showed that an increase in the oxygen content in the working mixture causes an increase in the transmittance, which means an increase in the photocatalytic activity of TiO2 films. However, the growth stops at a concentration values of 70% Ar +30% O2. This effect is explained by the findings of the research into the obtained films with the use of an atomic force microscopy: the roughness of the samples surface increases from 3 nm at a concentration values of 90% Ar +10% O2 to 31 nm at concentration values of 70% Ar +30% O2 and 65% Ar +35% O2. The effect is due to the fact that the film having sufficient amount of oxygen becomes more rough and porous, which has a positive effect on the photocatalytic activity, since the rough film surface area in contact with the decomposed substance is greater. An increase in the oxygen concentration in the working mixture of more than 30% during the production of photocatalytic TiO2 films by reactive magnetron sputtering is not reasonable, since it does not lead to an increase in photocatalytic properties. Besides, the increase in the oxygen concentration in the magnetron discharge plasma results in an increase in the number of crystal defects in the produced film.