Physical properties of homogeneous TiO2films prepared by high power impulse magnetron sputtering as a function of crystallographic phase and nanostructure

Optical, photo-electrochemical, crystallographic and morphological properties of TiO 2 thin films prepared by high power impulse magnetron sputtering at low substrate temperatures (<65 °C) without post-deposition thermal annealing are studied. The film composition—anatase, rutile or amorphous TiO 2 —is adjusted by the pressure ( p ∼ 0.75–15 Pa) in the deposition chamber. The different crystallographic phases were determined with grazing incidence x-ray diffractometry. The surface morphology and size of TiO 2 grains/clusters were imaged with atomic force microscopy. Basic plasma parameters were determined by means of the time-resolved Langmuir probe technique. The power density influx on the substrate was estimated from calorimetric probe measurement. The data from calorimetric probe measurements and time-resolved Langmuir probe served as input parameters for the calculation of influx contributions of particular species. The band-gap energy E g depends on the film composition and crystallographic phase. Optical parameters (refractive index n + i k , transmittance T , reflectance R and absorbance A ) are measured as functions of photon energy in the UV–Vis range by spectroscopic ellipsometry. For the rutile and anatase films agreement with the respective bulk phase is found. Incident photon-current conversion efficiency determined by photo-electrochemical measurements reached the highest values (0.312) for the anatase film.