Effect of liquid level and laser power on the formation of spherical alumina nanoparticles by nanosecond laser ablation of alumina target

Alumina nanoparticles (NPs) were synthesized by laser ablation of a bulk α-alumina (corundum) target immersed in distilled water using nanosecond laser pulses of 1064-nm wavelength. We investigated the effect of laser power and water column above the target. Synthesized particles were analyzed regarding particle shape and size distributions with scanning electron and transmission electron microscopy. Ablated NPs were spherical in shape and the average particle size ranged from 12 to 18 nm at varied laser power and water levels, although a very small number of melted droplets of submicron spheroids and irregular-shaped cracked particles were observed. X-ray diffraction analysis was conducted, which shows mainly the peaks of α-Al2O3 and minor peaks of γ-Al2O3. Phase identification of NPs, using high-resolution transmission electron micrograph lattice images and fast Fourier transform exhibits both metastable γ-Al2O3 and stable α-Al2O3 phases.