Photocatalytic activity of TiO2 deposited by reactive HiPIMS with long target-to-substrate distance

Reactive High Power Impulse Magnetron Sputtering (HiPIMS) of TiO2 thin films was carried out to investigate the influence of ion parameters and the deposition temperature on the film crystallinity and photocatalytic performance. In order to limit unintentional substrate heating, a deposition setup with long target-to-substrate distance was used. Different HiPIMS pulse configurations, deposition temperatures and substrate bias were evaluated. TiO2 films prepared by pulsed dc magnetron sputtering were used as reference. Films deposited at room temperature were all found to be X-ray amorphous, and a minimum temperature of 200 degrees C was needed for film crystallization irrespective of the mode of operation. This is attributed to the relatively long target-to -substrate distance of 180 mm used in this work. The growth of a specific polymorph was shown to be depen-dent on the operation mode, where a high oxygen partial pressure was ideal for anatase formation. The pho-todegradation rates were, as expected, found to be highest for crystalline samples, where single-and mixed-phase films yielded similar rates. Furthermore, the photodegradation rates of HiPIMS films deposited without substrate heating could be enhanced up to 3 times as compared to the corresponding pulsed dc reference film. The ion assistance in HiPIMS is also beneficial at moderate temperatures, here 200 degrees C, where an improved crystallinity as compared to pdcMS, was observed