Figure 3. Charge separation and hydrodynamic instability in the Petri dish at the Leidenfrost condition.

(a) Charge curves of the aqueous solution (the 10 mM experiment, 50 ml) measured inside the Petri dish at conventional heating (heating from 25 up to 300 °C) compared to that measured in the Petri dish at 300 °C (that is, the Leidenfrost temperature); (b) Cross-sectional thermographic view of the solution inside the Petri dish at 300 °C shows different colours corresponding to different temperatures (in °C) (scale bar, 3 mm); (c) A schematic illustrating the main stages of the Leidenfrost mechanism in our study compared to those of the La Mer mechanism. In our technique, very high concentration of ions in the overheated zone and very fast nucleation lead to a narrow size distribution and large amount of the fabricated particles. On the other hand, huge availability of reactants within the cold region, and reduction of ions that is catalysed by the already formed nanoclusters result in the uniform growth of the particles whose size is tailored by the solute concentration. (d) SEM image of the dual sized ZnO₂ nanoparticles (marked by I and II signs, respectively) synthesized during the eruption and growth process (scale bar, 2 μm); (e) TEM micrographs depicting a representative overview of the sample (left; scale bar, 20 nm) and HRTEM micrograph depicting ca. 50 nm hollow spheres produced by electron beam impact (upper right; scale bar, 10 nm), and corresponding Fourier Transform (lower right) signifying clustering of nanoparticles (labels a through f correspond to weak and strong reflections of ZnO and ZnO₂ crystalline planes); (f) Time-resolved ED data under low-dose illumination (∼1 s illumination time for each image; the marks are attributed to a reflection at d=1.756 Å being characteristic for ZnO₂).