Tailoring the shape of colloidal gold particles with nanosecond-pulsed laser light

Abstract

Modification of metal nanoparticles with laser light has been a well-known technique for several years. In this paper, we present our recent studies on tailoring the shape of colloidal gold particles with nanosecond-pulsed laser light. The underlying method is based on the shape and size dependent optical properties of metal nanoparticles, i.e. the excitation of surface plasmon polariton resonances. Thus, laser irradiation with a pre-determined photon energy excites and heats nanoparticles of certain shapes and sizes selectively. This heating leads to diffusion and, for sufficiently high fluences, to evaporation of surface atoms. In our experiments, colloidal gold particles were prepared by chemical reduction of a gold salt resulting in nanoparticles with different sizes and shapes. Subsequently, the colloidal gold particles were irradiated with nanosecond-pulsed laser light. In all cases, a significant reduction of the line width of the surface plasmon polariton resonance has been observed. This reflects a narrowing of the shape distribution of the particles. For example, irradiation with a photon energy of 2.16 eV and a fluence of (58 ± 2) mJ/cm² leads to a reduction of the width of the surface plasmon resonance from 0.30 eV to 0.22 eV (HWHM) due to a reshaping of the nanoparticles. This has also been confirmed by TEM measurements. Also, a size reduction of the nanoparticles has been observed.