Interrelationship between Densification, Crystallization, and Chemical Evolution in Sol‐Gel Titania Thin Films

The mechanisms contributing to densification during non-isothermal heat treatments in sol-gel titania films have been studied. At low temperatures, shrinkage is attributed to condensation reactions between hydroxyls located primarily within the oxide skeleton. At higher temperatures, densification is due to both continued condensation between surface hydroxyls and structural relaxation. Shrinkage stops when films attain a level of crystallinity corresponding to the percolation threshold. At conventional rates, densification is delayed by faster heating; however, at very fast heating rates provided by rapid thermal annealing (8000°C/min), condensation is highly arrested and densification is faster. Similarly, the onset of crystallization increases with conventional heating rates, but crosses over to a lower temperature with rapid thermal annealing.