The mechanisms of picosecond laser fragmentation of gold nanoparticles in water are investigated in a closely integrated atomistic simulations and time-resolved X-ray probing. The results of this joint computational and experimental study reveals a sequence of nonequilibrium processes triggered by the laser irradiation, from heating, melting, and resolidification of nanoparticles proceeding under conditions of strong superheating and undercooling, to evaporation of Au atoms followed by condensation into atomic clusters and small satellite nanoparticles, and to the regime of rapid (explosive) phase decomposition of superheated nanoparticles into small liquid droplets and vapor phase atoms. The transition to the phase explosion fragmentation regime is signified by prominent changes in the small-angle X-ray scattering profiles measured in experiments and calculated in simulations. A good match between the experimental and computational diffraction profiles gives credence to the physical picture of the cascade of thermal fragmentation regimes revealed in the simulations.
|