Crystal phases of TiO2 ultrafine particles prepared by laser ablation of solid rods

Titanium dioxide ultrafine particles (UFPs) are produced by pulsed laser ablation of titanium or titanium dioxide (anatase and rutile) rods in an atmosphere of He or O-2/He mixture. The collected UFPs on cellulose membrane filters at the exit of the ablation chamber are analyzed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The TiO2 particles produced are composed of very small particles (diameter: 10-50 nm) that are completely anatase, irrespective of the rod material, and relatively large particles (diameter: 100 nm-1 mum) that are a mixture of anatase and rutile. The large particles consist of the direct strip-off fragments coming from the rod surface. The particles obtained from the laser ablation on TiO2 rods in an atmosphere of He contains gray particles that are supposed to be amorphous TiO2 (x < 2). In the presence of O-2 in the ablation chamber, these oxygen defects in amorphous TiO2 are stabilized and anatase UFPs are formed. These results suggest that the crystal phase of the products can be controlled by adjusting the rod material and the gases used in the ablation process.