Laser-Assisted Synthesis of Colloidal FeWx Oy and Fe/Fex Oy Nanoparticles in Water and Ethanol.

Homogeneous polycrystalline Fex Oy nanoparticles were generated by ablation of iron targets in water by nanosecond laser pulses at 532 nm. In ethanol, crystalline core-shell Fe/Fex Oy structures with size medians around 20 nm were produced. The ablation of FeWx Oy targets in water resulted in crystalline hollow shells and homogeneous FeWx Oy nanoparticles. In contrast, amorphous core-shell FeWx Oy nanoparticles with a median size of 17 nm were produced in ethanol. The size distribution of both the Fex Oy and the FeWx Oy particles showed a slight dependence on fluence and pulse number. This may be related to primary and secondary ablation and modification mechanisms.

Laser-Assisted Synthesis of Colloidal Ni/NiOx Core/Shell Nanoparticles in Water and Alcoholic Solvents.

The nanosecond-pulse laser-assisted generation of Ni/NiOx core/shell nanoparticles (NPs) in water and alcoholic fluids can yield colloidal solutions without surfactants. The size distribution can be controlled by the nature of the alcohol, the number of laser pulses and the laser fluence. The incubation of the nickel target ablation in liquid contact shows a dependence on the carbon number of the respective alcohol. The laser-generated NPs consist of crystalline nickel cores with face-centred cubic patterns and stacking fault defects surrounded by nickel oxide shells. The solvent butanol, in contrast to ethanol and isopropanol, yields a narrow, nearly unimodal, size distribution. The majority of NPs have low size distributions, with medians in the range of 10-20 nm. These can be related to a metal ablation plume interacting with a supercritical liquid that decelerates the ejected material in a low-density metal-water mixing region. NPs in the range above 30 nm result in a minority distribution tail that strongly depends on the fluid nature, the pulse number and the fluence. This coarse NP set may be correlated with the rupture of a superheated molten-metal layer into larger entities.