The effect of type and concentration of modifier in supercritical carbon dioxide on crystallization of nanocrystalline titania thin films

Abstract

Nanostructured TiO2 anatase thin films were directly prepared using supercritical carbon dioxide (scCO(2)) modified by organic solvent and water in two step processing. Organic solvent used as scCO(2) modifier at 30 MPa and 40 degrees C in the first step of processing was in the second step changed to water with simultaneous temperature increase to 150 degrees C which caused anatase thin films crystallization. The effect of the type of modifier (water, methanol, ethanol and acetone), concentration of modifier (5-40 wt.%) in scCO(2) and the amount of scCO(2) (50-200 g) passed through the high pressure column as well as the type of substrate (soda-lime glass and monocrystalline Si) on microstructure and purity of TiO2 thin films were examined in both steps of processing. The prepared thin films were characterized with respect to their (micro)structural properties by Raman spectroscopy as well as X-ray diffraction, to their wettability by contact angle measurements and to their morphology by high resolution transmission electron microscopy.