GENERATION OF METAL NANOPARTICLES BY LASER-ABLATION OF MICROSPHERES

We describe excimer laser ablation of 1-10 mu m diameter permalloy (Ni 81 %:Fe 19 %) and gold microparticles (2 mu m diameter) under normal atmospheric conditions, and for glass nanoparticles in supersonic jets and vacuum. The ejected nanoparticles were collected on silicon subst rates and measured using an SEM. Results showed that mean particle dia meters were in the range from 60 to 116 nm, and that the particle-size distributions were closely log-normal. For gold particles, the mean p article size increased with laser fluence from 80 nm at 3.1 J cm(-2) t o a mean size of 116 nm at 10 J cm(-2); inverse to the dependence we o bserved for glass microspheres. The ratio of the standard deviation to mean size for the distribution of gold particles also increased from 0.26 at 3.1 J cm(-2) to 0.4 at fluences of 10 J cm(-2). At the larger laser fluences these distributions appeared to be bimodal, consisting of smaller spheres and larger cubes, suggesting different physical mec hanisms for the production of nanoparticles. Results for permalloy par ticles were similar except the nanoparticles were spherical at all flu ences. (C) 1998 Elsevier Science Ltd. All rights reserved.