Effects on post-synthesis treatment of the photochemistry of heteroepitaxial anatase TiO2 thin films

Al2O3 (001). Post-treatment of the TiO2 thin films by annealing and base wash maintained the heteroepitaxial structure. Annealing the thin films improved their crystallinity by healing point defects, coarsening grains, and increasing the oxygen content closer to the ideal Ti:2O stoichiometry. The photooxidizing ability of the films was evaluated using terephthalic acid (TA) as a hydroxyl radical scavenger, which generated 2- hydroxyterephthalic acid (TA-OH), a strong fluorophore. It was found that annealed anatase films are much more effective photooxidation catalysts than as-synthesized films. Electron paramagnetic resonance (EPR) spectroscopy showed that as-synthesized films had both hole and electron trap states while the annealed film had only hole traps. This implies that annealed films will be excellent electron transport materials for applications such as solar cells. In addition to XRD and EPR, each film was characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. In summary, bulk defects and surface composition play a major role in the photooxidation effectiveness of anatase thin films with {001} facets and their potential use as electron transport layers in devices.Anatase TiO2 films with strong 001 texture and ~100% {001} facets at the surface were prepared on sapphire (001) substrates by a fluoride based hydrothermal route. X-ray diffraction (XRD) measurements revealed that anatase (001) grew in an epitaxial manner on sapphire (001) according to a domain matching epitaxy (DME) mechanism. This is the first report of the heteroepitaxial relationship anatase TiO2 (001)