Metal nanoparticles generated by laser ablation

We study a new method for producing ultrafine metal particles (nanoparticles) that employs Laser Ablation of Microparticles (LAM). Pulsed excimer laser radiation at 248 nm wavelength was used to ablate similar to 2 mu m feedstock of silver, gold, and permalloy(Ni-81%:Fe-19%) under both normal atmospheric conditions and in other gases and pressures. A model for nanoparticle formation by LAM is proposed that includes plasma breakdown anal shock-wave propagation through the initial microparticle. Behind the shock a large fraction of the original microparticle mass is converted to nanoparticles that diffuse to silicon substrates and TEM grids for collection and analysis. Nanoparticle morphologies are spherical except for gold nanoparticles >100 nm that are generally cubes. Electron micrographs of the samples were analyzed by computer-aided image processing to determine the effect of irradiation conditions on the nanoparticle size distribution. The results showed that mean particle diameters were normally in the range from 10 to 100 nm and that the particle size distributions were generally log-normal, with dispersion (diameter/standard deviation) ranging from 0.2 to 0.5. For metallic microparticle feedstock, the mean size of the produced nanoparticles generally increased with increasing laser fluence and were smallest for fluences not too far above the breakdown threshold. (C) 1998 Acta Metallurgica Inc.