Influence of ion beam current on the structural, optical, and mechanical properties of TiO₂ coatings: ion beam-assisted vs conventional electron beam evaporation

In this paper, comparative studies of selected properties of titanium dioxide (TiO₂) coatings deposited using electron beam evaporation (EBE) and ion beam-assisted deposition (IBAD) are presented. Post-process annealing at 800 °C was also conducted to examine its impact on the properties of the prepared coatings. After annealing at 800 °C, a transition from amorphous to the anatase phase occurred for all coatings. In particular, an increase in ion beam current led to a reduction in crystallite size by approximately 30% compared to coatings prepared by conventional EBE process. The average anatase crystallite size for annealed films was in the range of 30.8 to 43.5 nm. A detailed SEM analysis of surface morphology and cross sections revealed that the TiO₂ films prepared by IBAD had smaller, rounded grains and were denser compared to those deposited by EBE. Optical properties showed high transparency of 77-83% in the visible wavelength range for all as-prepared thin films. However, annealing caused a decrease of the transparency level by 32% for films deposited by EBE, while for films from the IBAD process the decrease was less than 10%. The use of an ion gun increased the hardness of the TiO₂ films from 2.4 to 3.5 GPa (<i>I</i> _ibg = 4 A). Although a similar relationship was observed for coatings after annealing, hardness values were lower than for as-deposited coatings. The most notable differences were observed in the abrasion tests, where the IBAD process significantly enhanced the abrasion resistance of the coatings. This research highlights the potential of IBAD to prepare dense, adhesive, and durable TiO₂ coatings with improved optical and mechanical properties, suitable for applications requiring enhanced wear resistance.