Mechanisms and advanced photothermal modelling of laser-induced shape transformations of colloidal gold nanorods by nanosecond laser pulses

We propose an advanced photothermal model based on a modified Takami model (MTM) to explain the mechanisms of shape changes of colloidal gold nanorods (NRs) induced by nanosecond laser pulses. This model takes into account the orientation of NRs, the radiative and convective losses, and the phase transitions of NRs. It was applied to the determination of the evolution of temperature and the shape and size transformations of NRs during the laser exposure. A series of measurements arising from the interaction between Au NRs and nanosecond laser pulses were analyzed by TEM measurements and the MTM model. We have demonstrated that the fragmentation and reshaping processes govern the nanoparticle (NP) shape. At high laser fluence, the complete fragmentation leads to a population of nearly spherical NPs, while at a moderate laser fluence, the partial fragmentation and reshaping processes generate a bimodal distribution. At low laser fluence, uncommon φ-shape NPs were produced as a result of the competition of cooling and reshaping processes. We also demonstrated that it is possible by the MTM model to determine the laser fluence required to suppress some specific NR shapes and to predict the NP size and shape distributions obtained after the laser exposure.