Effect of a liquid environment on single-pulse generation of laser induced periodic surface structures and nanoparticles†
The effect of a liquid environment on the fundamental mechanisms of surface nanostructuring and generation of nanoparticles by single pulse laser ablation is investigated in a closely integrated computational and experimental study. A large-scale molecular dynamics simulation of spatially modulated ablation of Cr in water reveals a complex picture of the dynamic interaction between the ablation plume and water. Ablation plume is found to be rapidly decelerated by the water environment, resulting the formation and prompt disintegration of a hot metal layer at the interface between the ablation and water. A major fraction of the ablation plume is laterally redistributed and redeposited back to the target, forming smooth frozen surface features. Good agreement between the shapes of the surface features predicted in the simulation and the ones generated in single pulse laser ablation experiments performed for Cr in water supports the mechanistic insights revealed in the simulation. The results of this study suggest that the presence of a liquid environment can eliminate the sharp features of the surface morphology, reduce the amount of the material removed from the target by more than an order of magnitude, and narrow down the nanoparticle size distribution as compared to laser ablation under vacuum. Moreover, the computational predictions of the effective incorporation of molecules constituting the liquid environment into the surface region of the irradiated target and the generation of high vacancy concentrations, exceeding the equilibrium levels by more than an order of magnitude, suggest a potential for hyperdoping of laser-generated surfaces by solutes present in the liquid environment.