The effect of magnetic fields on the products of laser ablation

Structures of gold nanoparticles were formed by laser ablation of bulk gold immersed in water. An excimer laser with a wavelength of 351 nm and a pulse energy of 7 mJ was used. Ablation was performed in two configurations: without and with an external 0.2 T magnetic field parallel to the ablation plume. Both configurations result in structures that include chains of aggregated nanoparticles, but to different degrees. Ablation in a magnetic field results in a higher fraction of spherical nanoparticles and shorter nanowires, compared to the nanowire networks formed in the absence of the field. This can be explained by magnetic confinement of the plasma during plume expansion. A model explaining nanowire formation and dependence on fluence and magnetic field is proposed.