Scientific Reports: Combined time-resolved X-ray radiography and SAXS exploring Pulsed-Laser Ablation in Liquid
Laser ablation synthesis of nanoparticles in liquid is a route for production of nanoparticles from a wide range of material classes without any contaminant. The underlying process is meanwhile not well understood because of the interplay of structure formation within different length and time scales. Pulsed-laser ablation creates dense plasma on the surface, but also a bubble of evaporated liquid, which both mediate and restrict the formation of particles from ejected material. We have combined fast time-resolved X-ray radiography at the ANKA TOPO-TOMO beamline with pulsed Small angle X-ray scattering at the SLS cSAXS beamline to determine structural dynamics from the millimeter down to the nanometer time scale.
Animation of the time-resolved X-ray radiography of the cavitation process after laser-irradiation of a silver target. The laser beam arrives from top in the center at the image at a delay of 0. The flat metal target surface is located slightly above the black bar at the bottom. Field of view is about 3.2 x 1.8 mm.
The figure shows an animation of the radiographic contrast as function of delay relative to laser impact (Nd:YAG nanosecond laser with 10 mJ pulse energy and 200 µm focus size on the target.)
Combining the millimeter scale with the temporal distribution of particles several observations shed light on the particle genesis: (i) A first vapor bubble is filled with small (approx. 10 nm) particles and forms a barrier against dispersion in the liquid, (ii) during bubble collapse and rebound most of the particle mass is also retracted towards the target and massive agglomeration sets in, and (iii) strong particle release is only evident within a third, deformed bubble, which forms a jet of material perpendicular to the surface.
These observations allow for a discussion of main goals of optimizing particle synthesis: the particle yield and size distribution.
Scientific Reports, October/November 2015, DOI: 10.1038/srep16313
[Link: www.nature.com/articles/srep16313 ]
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