Pulsed Laser-Induced Size Reduction of Aqueous Gold Nanoparticles

Abstract

Pulsed laser-induced morphological transformation and size-reduction of colloidal gold nanoparticles in the aqueous phase were investigated using transient absorption spectroscopy and transmission electron microscopy (TEM). Femtosecond laser-induced fragmentation of gold nanoparticles within 100 ps after the laser pulse is interpreted in terms of the Coulomb explosion mechanism. On the other hand, nanosecond laser-induced size-reduction of gold nanoparticles is in good agreement with the photothermal evaporation mechanism that is based on heating of particles to temperatures above the boiling point of gold (3100 K). Here, the experimentally observed fragmentation thresholds were well-reproduced by simulations based on electron and lattice temperature models and by considering the dissipation of heat into the surrounding medium. The numerical method described herein has the advantage of identifying the fragmentation mechanism by considering pulse duration- and energy- dependent thresholds. To-date there is no other convenient measures to distinguish between the photothermal evaporation and the Coulomb explosion mechanisms.