Laser-Induced Conversion of Au Powders to Highly Stable Nanoparticles with a Narrow Size Distribution

We show that Au nanopowders with arbitrary shapes can be converted into nanoparticles with a narrow size distribution by using a nanosecond Nd:YAG laser. Commercial Au powders were first dissolved in deionized water and irradiated with laser pulses at 532 nm. This converted the powder clusters into spherical particles with sizes ranging from 100 nm to a few micrometer. Subsequent irradiation of these Au spheres with 1064-nm pulses produced a larger quantity of nanoparticles with fairly uniform sizes. The overall conversion process could be well explained by the photothermal melting-evaporation mechanism. The fabricated Au particles exhibited a mean size of 15 nm, with a standard deviation of 5.5-7.2 nm. The Au colloidal solution was highly stable against agglomeration, and the particles remained well-dispersed in water for 1 month. This behavior is attributed to surface charges introduced during the laser process.