The present study investigates the impact of post annealing of TiO 2 nanoparticulate lms on their crystallinity, mechanical strength, and morphology. Non-agglomerated and amorphous TiO 2 nanoparticles of 46 nm diameter were synthesized in a plasma eld, and were subsequently deposited on substrates to form nanoparticulate lms. The lms were annealed at various temperatures in the range of 100-1,200°C. Phase transformations from amorphous-to-anatase and from anatase-to-rutile were observed at

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... and at 1,000°C, respectively. The high rutile transformation temperature was considered to be due to a tensile eld induced by shrinkage of the lm. The as-deposited lm and the lms annealed at below 400°C had poor mechanical strength. Conversely, the lms annealed at over 500°C were strengthened by necking of the nanoparticles. The size of nanoparticles changed with increasing temperature. Annealing at 100-300°C caused the nanoparticles to shrink to approximately 30 nm. The nanoparticle diameters changed only slightly when annealed at 400-600°C because the annealing time was insu cient for changes to manifest. Annealing at 700-900°C caused the nanoparticle diameter to increase to approximately 50 nm because of sintering and coalescence of the nanoparticles. The diameter of the nanoparticles annealed at over 1,000°C became approximately 200 nm because of densi cation during the anatase-to-rutile transformation. The porosities of the lms annealed at below 900°C were over 80%. However, the porosities of the lms annealed at over 1,000°C decreased signi cantly due to densi cation.