Tuning the size of aluminum oxide nanoparticles synthesized by laser ablation in water using physical and chemical approaches

Colloidal solution of nano-sized spherical Al(2)O(3) particles were produced by nanosecond laser ablation upon irradiation on a corundum target in a distilled water environment. The effects of target inclination along the direction of laser irradiation and defocusing of the laser beam have been investigated in this study. The effect of the pH of the aqueous solution has also been studied. Synthesized particles were analyzed using transmission electron microscopy (TEM) to investigate particle shape and size distributions. Ablated nanoparticles (NPs) were spherical in shape, with the average particle size ranging from 8 to 18 nm in different operating conditions. Target inclination resulted in a decrease in the average particle size. Laser defocusing at the same power and thus with reduced fluence caused a decrease in the average size and standard deviation (SD), whereas defocusing that maintained the same fluence caused the reverse effect. Phase identification of NPs performed with high resolution TEM lattice images and fast Fourier transform indicated both a metastable γ-Al(2)O(3) phase and a stable α-Al(2)O(3) phase. X-ray diffraction analysis was also performed, which showed peaks of both α-Al(2)O(3) and γ-Al(2)O(3) with the presence of α- and γ-AlO(OH) polymorphs in acidic and alkaline solution, respectively. Surface conditions of the ablated particles representing the acidic and alkaline conditions were found to have a significant influence on both the size and crystallographic phase, which indicates it may be possible to induce size and phase transitions by changing the surface chemistry.