Size and Shape Transformation of TiO2 Nanoparticles by Irradiation of 308-nm Laser Beam

TiO2 particles in a colloidal solution changed their size and shape upon irradiation of a 308 nm laser beam which corresponded to the inter-band absorption of the particles. The particles with a diameter size distribution between 170 to 1050 nm were transformed to smaller particles of approximately 10 nm diameter with a narrow size distribution. The particles of 2 nm diameter were also converted to the particles of 10 nm diameter. The irradiated particles were spherical, indicating that particles were melted upon laser irradiation. The threshold of laser fluence was observed for the size and shape transformation of the particles, which was several times larger than the energy required to melt the particles. Agglomeration of the particles, which was controlled by pH of the solution, enlarged the average size and broadened the range of size distribution of the irradiated particles. The mechanism determining the size of the irradiated particles has been discussed.