Reactive ballistic deposition of porous TiO2 films:: Growth and characterization

Nanoporous, high-surface area films of TiO2 are synthesized by reactive ballistic deposition of titanium metal in an oxygen ambient. Auger electron spectroscopy (AES) is used to investigate the stoichiometric dependence of the films on growth conditions (surface temperature and partial pressure of oxygen). Scanning and transmission electron microscopies show that the films consist of arrays of separated filaments. The surface area and the distribution of binding site energies of the films are measured as functions of growth temperature, deposition angle, and annealing conditions using temperature programmed desorption (TPD) of N-2. TiO2 films deposited at 50 K at 70 degrees from substrate normal display the greatest specific surface area of similar to 100 m(2)/g. In addition, the films retain greater than 70% of their original surface area after annealing to 600 K. The combination of high surface area and thermal stability suggests that these films could serve as supports for applications in heterogeneous catalysis.