Analysis of the impact of post-process modifications on the properties of TiO2 thin films with high-temperature stable anatase phase deposited by the electron beam evaporation method

Abstract

The paper describes the structural, optical, tribological, and mechanical properties of as‑prepared and annealed titanium dioxide (TiO₂) coatings. TiO₂ films were deposited by the electron beam evaporation (EBE) and additionally annealed at a temperature up to 800 °C using a tubular furnace. X-ray diffraction (XRD) analysis identified the amorphous phase of coatings as-prepared and annealed at 200 °C. The phase transition to anatase occurred at 400 °C, while annealing at 600 °C and 800 °C did not induce a phase transition to the rutile phase. The crystallite size increased with an annealing up to 40.4 nm at 800 °C. Raman spectroscopy confirmed the anatase phase in thin films annealed at 400 °C and above. A scanning electron microscope (SEM) images revealed surface morphology and grain structure changes after post-process high-temperature annealing. The optical transmission measurements showed a redshift in the fundamental absorption edge with increasing annealing temperature, accompanied by a decreased transparency level. The value of an optical band gap energy (E_g^opt) decreased to 2.77 eV for films annealed at 800 °C. Tribological tests revealed reduced scratch resistance with higher annealing temperatures, which was attributed to increased surface roughness and coating removal. Nanoindentation measurements showed a decrease in hardness with annealing temperature, attributed to changes in crystallite size and surface morphology. This comprehensive analysis of TiO₂ thin-film coatings showed that the post-process annealing should be carefully controlled for films used in optoelectronic applications.