Creation of tungsten and platinum nanoparticles from nanosecond plasmas in water

Nanosecond plasmas ignited inside water at tungsten and platinum/iridium electrode tips are used to create very small nanoparticles with radii around 1 nm. Due to the very high power density of 10¹⁶ W m^–2 at an electrode hot spot with a diameter of 10 µm, the surface is ablated during the short plasma pulse, and the metal vapour expands in the cavitation bubble after the plasma. This creates a very large cooling rate and the formation of nanoparticles by condensation from the created metal vapour. Finally, the nanoparticles disperse in the liquid. This sequence is quantified by measuring the net tip erosion by shadowgraphy and the created nanoparticles by transmission electron microscopy and x-ray photoelectron spectroscopy. The condensation process is modelled in conjunction with cavitation theory for the expanding cavitation bubble, which shows very good agreement with experimental data.