Dissociation and Aggregation of Gold Nanoparticles under Laser Irradiation

Gold nanoparticles having an average diameter of ∼8 nm were prepared in an aqueous solution of sodium dodecyl sulfate by laser ablation at 1064 nm of a gold metal plate and were irradiated by a laser at 532 nm for size-reduction of the gold nanoparticles produced by laser ablation. The diameters of the gold nanoparticles thus produced were measured directly by electron microscopy, while the average diameter was estimated from the optical absorption spectrum of the solution containing the nanoparticles with the aid of the Drude theory of a conducting droplet. The average diameter of the nanoparticles was found to decrease toward the smallest possible diameter as the laser shot increases; in this condition, the resulting nanoparticles have comparable diameters. In addition, the smallest possible diameter was found to decrease with the laser fluence. It was also shown that aggregation of the nanoparticles is not negligible when the laser fluence is high. In conclusion, nanoparticles with an average diameter was pulverized into smaller nanoparticles with a desired average diameter and a narrow distribution by a proper selection of the laser fluence and the laser shots. The mechanism of the particle pulverization was proposed.