Physical properties of porous titania films composed of nanoparticle aggregates

Highly porous films of titania composed of nanoparticle aggregates were synthesized via gas-to-particle conversion and particle-precipitated chemical vapor deposition. The films were annealed in air for 12 h at temperatures ranging from 400 to 1000 °C. Atomic force microscopy was used to determine the Young's modulus and hardness of both the as-synthesized and annealed films. The Young's modulus and hardness of the as-synthesized films were 4.0 ± 0.4 MPa and 0.026 ± 0.003 MPa, respectively. There was no significant change in either modulus or hardness upon annealing until the films were annealed at a temperature of 1000 °C. The Young's modulus and hardness of these films were 56 ± 6 MPa and 0.10 ± 0.01 MPa, respectively. Results from dynamic light scattering measurements of aggregate size and surface area measurements suggest that annealing at 1000 °C leads to increased networking between distinct nanometer-scale titania aggregates, which strengthens the film.