Titania nanoparticles prepared with pulsed laser ablation of rutile single crystals in water

The pulsed laser ablation (PLA) experiments of rutile single crystal surfaces were carried out in water solution to prepare nanosized titania particles. The solvated PLA species were transparent as produced and changed to a lighter blue solution with some precursors for filamentous species (in several days), then finally changed to white enlarged filamentous species (in 2-4 weeks). The solvated PLA species were measured as uniform nanoparticles with a size below 10 nm by TEM measurements and showed the absorption-photon energy relation for the direct transition with a band gap of 5.3-5.5 eV. The band-gap values were elucidated with quantum confinement size effects. It was assumed that the primary solvated species should have a size of about 1 nm and they were agglomerated to be the secondary species. The Mie scattering is responsible for the "blue" color, which proves that the size enlargement process exists on the PLA species in water. The filamentous species are composed of mainly the anatase form, which was analyzed with Raman spectroscopy. The XPS results indicate that the Ti species are tetravalent and bonded to oxygen atoms with O 1s binding energy at around 530 eV as TiO2. They were found to be composed to about 1 mum diameter with gathering nanosized particles on SEM pictures. The thin films composed of the PLA filamentous species showed no band cap increase. The process for PLA of rutile in water was studied with different temperatures (T in K) to elucidate the effect of viscosity (eta). The yield of PLA species in water decreases nearly linearly with the ratio of T/eta representing the diffusion coefficient of the solvated species. The result implies that the PLA species are confined in a media not diffused into water solution.