PREPARATION OF GOLD NANOPARTICLES WITH NARROW SIZE DISTRIBUTIONS AND WELL DEFINED SHAPES

Abstract

In this contribution, we present the results of recent experiments with the objective of tailoring the size and shape of gold nanoparticles with nanosecond laser pulses. The technique is based on the size and shape dependent surface plasmon resonance frequencies of metal nanoparticles. In our recent experiments gold nanoparticles were prepared by deposition of atoms on dielectric substrates followed by diffusion and nucleation. This usually results in ensembles of oblate nanoparticles with a broad size and shape distribution. Irradiating the gold particles during growth with nanosecond laser pulses makes it possible to produce nanoparticles with a predetermined axial ratio independent of size. For example, irradiating gold nanoparticles with a photon energy of 1.65 eV during growth stabilizes an axial ratio of a/b = 0.14, a being the short axis and b the long axis of the ellipsoidal nanoparticles. Furthermore, post-growth irradiation permits tailoring the average size of the nanoparticles by laser induced surface diffusion and evaporation of atoms. In principle, it is possible to eliminate all particles of undesired sizes by choosing the appropriate photon energies. We demonstrate that narrowing of the width of the surface plasmon resonance from initially 0.52 eV (half width at half maximum) to 0.2 eV is possible by using a single laser frequency. Combining both methods, i.e. laser irradiation during and after growth, finally results in a narrow size and shape distribution of the particles.