Explosive vaporization of metallic nanostructures on a surface by nanosecond laser heating under fluids

2021 
The rapid laser heating of materials beyond their boiling point has been associated with a variety of interesting phenomena, such as supersaturated vapor formation and explosive evaporation. Here, we study the nanosecond pulsed laser heating of Ag nanopyramids and thin films deposited on quartz substrates under various fluids. Rapid heating of Ag nanopyramids in vacuum demonstrated that a large fraction of the vaporized material was redeposited onto the substrate, confirming an explosive vaporization process. When the Ag nanostructures were heated under bulk fluids like water and glycerol, an increased localization of the vaporized material was observed. We hypothesize that the size of the bulk fluid’s vapor zone surrounding the metallic nanoparticles, which, in turn, is determined by the thermal diffusivity of the bounding fluid, confines the metal vaporization process. While a large amount of material is vaporized in this process, the redeposited material particles show a significant decrease in size and an increase in particle density, by nearly 250% in going from air to glycerol. This behavior of the metal vaporization under bounding fluids could be used to tailor the size and density of nanoparticles on a surface as well as investigate the highly non-equilibrium process of explosive vaporization.
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