Fluence dependence of the tailoring of colloidal gold particles with nanosecond-pulsed laser light

Abstract

We have studied the fluence dependence of the laser tailoring of colloidal gold particles with radii below <i>R</i> = 25 nm. For this purpose gold nanoparticles in solution have been irradiated with nanosecond-pulsed laser light applying fluences between <i>F</i> = (25 &plusmn; 2) mJ/cm² and <i>F</i> = (49 &plusmn; 2) mJ/cm². In general, laser tailoring is based on the size and shape dependent localized surface plasmon polariton resonance (LSPPR) of metal nanoparticles. Thus, irradiation with a given laser photon energy is absorbed only by nanoparticles whose LSPPR coincides with the photon energy of the laser light. The absorbed light is rapidly converted into heat, leading to diffusion and evaporation of surface atoms, which permits selective tailoring of nanoparticles. In this contribution, we demonstrate that irradiation of small gold nanoparticles with ns-pulsed laser light, at moderate fluences between <i>F</i> = (25 &plusmn; 2) mJ/cm² and <i>F</i> = (41 &plusmn; 2) mJ/cm², results in a shape change from non-spherical towards spherical particles. At the same time a defined size reduction of the nanoparticles from (<i>R</i>) = 17.2 nm to (<i>R</i>) = 14.8 nm takes place. Higher fluences initiate nanoparticle coalescence.