Physical insight in the fluence-dependent distributions of Au nanoparticles produced by sub-picosecond UV pulsed laser ablation of a solid target in vacuum environment

摘要

Deposition of Au nanoparticles (NPs) through UV ultra-short-pulse laser ablation in vacuum is a methodology suitable for obtaining high purity supported plasmonic NPs with a superb adherence to both planar and patterned substrates. Furthermore, the peculiarity that upon sub-picosecond laser irradiation NPs form directly within the target leads to narrow and controlled size-distribution. While extensive literature theoretically models phase changes and pressure relaxation of metal targets under sub-picosecond irradiation, the evolution of the nanostructured deposit through different ablation regimes is poorly documented experimentally.In this paper, besides modeling the temporal evolution of electron and lattice temperature following sub-picosecond laser pulse irradiation of Au bulk at the threshold ablation fluence (0.1 J/cm(2)), we report an accurate statistical, morphological and structural characterization of the AuNP distributions as a function of the laser fluence tuned from 0.1 to 3 J/cm(2) to drive the target through two ablation regimes. The occurrence of photomechanical spallation and phase explosion at low and high fluence, respectively, is correlated with the evolution of the NP deposits, which are discussed by providing a physical insight in the interplay between fluence-driven ablation regimes of the target, arrangement kinetics of the deposited species (NPs and vapour species) and (crystalline or amorphous) phase of the NPs. This knowledge is key for controlling the surface plasmon resonance response of AuNPs depending on the designed application.